prax-query 0.10.0

#![allow(dead_code)]

//! Nested write operations for managing relations in a single mutation.
//!
//! This module provides support for creating, connecting, disconnecting, and updating
//! related records within a single create or update operation.
//!
//! # Example
//!
//! ```rust,ignore
//! use prax_query::nested::*;
//!
//! // Create a user with nested posts
//! let user = client
//!     .user()
//!     .create(user::create::Data {
//!         email: "user@example.com".into(),
//!         name: Some("John Doe".into()),
//!         posts: Some(NestedWrite::create_many(vec![
//!             post::create::Data { title: "First Post".into(), content: None },
//!             post::create::Data { title: "Second Post".into(), content: None },
//!         ])),
//!     })
//!     .exec()
//!     .await?;
//!
//! // Connect existing posts to a user
//! let user = client
//!     .user()
//!     .update(user::id::equals(1))
//!     .data(user::update::Data {
//!         posts: Some(NestedWrite::connect(vec![
//!             post::id::equals(10),
//!             post::id::equals(20),
//!         ])),
//!         ..Default::default()
//!     })
//!     .exec()
//!     .await?;
//!
//! // Disconnect posts from a user
//! let user = client
//!     .user()
//!     .update(user::id::equals(1))
//!     .data(user::update::Data {
//!         posts: Some(NestedWrite::disconnect(vec![
//!             post::id::equals(10),
//!         ])),
//!         ..Default::default()
//!     })
//!     .exec()
//!     .await?;
//! ```

use std::fmt::Debug;
use std::marker::PhantomData;

use crate::error::QueryResult;
use crate::filter::{Filter, FilterValue};
use crate::sql::quote_identifier;
use crate::traits::{Model, QueryEngine};

/// Represents a nested write operation for relations.
#[derive(Debug, Clone)]
pub enum NestedWrite<T: Model> {
    /// Create new related records.
    Create(Vec<NestedCreateData<T>>),
    /// Create new records or connect existing ones.
    CreateOrConnect(Vec<NestedCreateOrConnectData<T>>),
    /// Connect existing records by their unique identifier.
    Connect(Vec<Filter>),
    /// Disconnect records from the relation.
    Disconnect(Vec<Filter>),
    /// Set the relation to exactly these records (disconnect all others).
    Set(Vec<Filter>),
    /// Delete related records.
    Delete(Vec<Filter>),
    /// Update related records.
    Update(Vec<NestedUpdateData<T>>),
    /// Update or create related records.
    Upsert(Vec<NestedUpsertData<T>>),
    /// Update many related records matching a filter.
    UpdateMany(NestedUpdateManyData<T>),
    /// Delete many related records matching a filter.
    DeleteMany(Filter),
}

impl<T: Model> NestedWrite<T> {
    /// Create a new related record.
    pub fn create(data: NestedCreateData<T>) -> Self {
        Self::Create(vec![data])
    }

    /// Create multiple new related records.
    pub fn create_many(data: Vec<NestedCreateData<T>>) -> Self {
        Self::Create(data)
    }

    /// Connect an existing record by filter.
    pub fn connect_one(filter: impl Into<Filter>) -> Self {
        Self::Connect(vec![filter.into()])
    }

    /// Connect multiple existing records by filters.
    pub fn connect(filters: Vec<impl Into<Filter>>) -> Self {
        Self::Connect(filters.into_iter().map(Into::into).collect())
    }

    /// Disconnect a record by filter.
    pub fn disconnect_one(filter: impl Into<Filter>) -> Self {
        Self::Disconnect(vec![filter.into()])
    }

    /// Disconnect multiple records by filters.
    pub fn disconnect(filters: Vec<impl Into<Filter>>) -> Self {
        Self::Disconnect(filters.into_iter().map(Into::into).collect())
    }

    /// Set the relation to exactly these records.
    pub fn set(filters: Vec<impl Into<Filter>>) -> Self {
        Self::Set(filters.into_iter().map(Into::into).collect())
    }

    /// Delete related records.
    pub fn delete(filters: Vec<impl Into<Filter>>) -> Self {
        Self::Delete(filters.into_iter().map(Into::into).collect())
    }

    /// Delete many related records matching a filter.
    pub fn delete_many(filter: impl Into<Filter>) -> Self {
        Self::DeleteMany(filter.into())
    }
}

/// Data for creating a nested record.
#[derive(Debug, Clone)]
pub struct NestedCreateData<T: Model> {
    /// The create data fields.
    pub data: Vec<(String, FilterValue)>,
    /// Marker for the model type.
    _model: PhantomData<T>,
}

impl<T: Model> NestedCreateData<T> {
    /// Create new nested create data.
    pub fn new(data: Vec<(String, FilterValue)>) -> Self {
        Self {
            data,
            _model: PhantomData,
        }
    }

    /// Create from field-value pairs.
    pub fn from_pairs(
        pairs: impl IntoIterator<Item = (impl Into<String>, impl Into<FilterValue>)>,
    ) -> Self {
        Self::new(
            pairs
                .into_iter()
                .map(|(k, v)| (k.into(), v.into()))
                .collect(),
        )
    }
}

impl<T: Model> Default for NestedCreateData<T> {
    fn default() -> Self {
        Self::new(Vec::new())
    }
}

/// Data for creating or connecting a nested record.
#[derive(Debug, Clone)]
pub struct NestedCreateOrConnectData<T: Model> {
    /// Filter to find existing record.
    pub filter: Filter,
    /// Data to create if not found.
    pub create: NestedCreateData<T>,
}

impl<T: Model> NestedCreateOrConnectData<T> {
    /// Create new create-or-connect data.
    pub fn new(filter: impl Into<Filter>, create: NestedCreateData<T>) -> Self {
        Self {
            filter: filter.into(),
            create,
        }
    }
}

/// Data for updating a nested record.
#[derive(Debug, Clone)]
pub struct NestedUpdateData<T: Model> {
    /// Filter to find the record to update.
    pub filter: Filter,
    /// The update data fields.
    pub data: Vec<(String, FilterValue)>,
    /// Marker for the model type.
    _model: PhantomData<T>,
}

impl<T: Model> NestedUpdateData<T> {
    /// Create new nested update data.
    pub fn new(filter: impl Into<Filter>, data: Vec<(String, FilterValue)>) -> Self {
        Self {
            filter: filter.into(),
            data,
            _model: PhantomData,
        }
    }

    /// Create from filter and field-value pairs.
    pub fn from_pairs(
        filter: impl Into<Filter>,
        pairs: impl IntoIterator<Item = (impl Into<String>, impl Into<FilterValue>)>,
    ) -> Self {
        Self::new(
            filter,
            pairs
                .into_iter()
                .map(|(k, v)| (k.into(), v.into()))
                .collect(),
        )
    }
}

/// Data for upserting a nested record.
#[derive(Debug, Clone)]
pub struct NestedUpsertData<T: Model> {
    /// Filter to find existing record.
    pub filter: Filter,
    /// Data to create if not found.
    pub create: NestedCreateData<T>,
    /// Data to update if found.
    pub update: Vec<(String, FilterValue)>,
    /// Marker for the model type.
    _model: PhantomData<T>,
}

impl<T: Model> NestedUpsertData<T> {
    /// Create new nested upsert data.
    pub fn new(
        filter: impl Into<Filter>,
        create: NestedCreateData<T>,
        update: Vec<(String, FilterValue)>,
    ) -> Self {
        Self {
            filter: filter.into(),
            create,
            update,
            _model: PhantomData,
        }
    }
}

/// Data for updating many nested records.
#[derive(Debug, Clone)]
pub struct NestedUpdateManyData<T: Model> {
    /// Filter to match records.
    pub filter: Filter,
    /// The update data fields.
    pub data: Vec<(String, FilterValue)>,
    /// Marker for the model type.
    _model: PhantomData<T>,
}

impl<T: Model> NestedUpdateManyData<T> {
    /// Create new nested update-many data.
    pub fn new(filter: impl Into<Filter>, data: Vec<(String, FilterValue)>) -> Self {
        Self {
            filter: filter.into(),
            data,
            _model: PhantomData,
        }
    }
}

/// Builder for nested write SQL operations.
///
/// The SQL emitters here currently bake in [`crate::dialect::Postgres`] —
/// nested writes are not yet wired into a live client, and the placeholder
/// syntax (`$N`) is Postgres-shaped. When this builder lands on the live
/// client path the dialect should thread through from the engine.
#[derive(Debug)]
pub struct NestedWriteBuilder {
    /// The parent table name.
    parent_table: String,
    /// The parent primary key column(s).
    parent_pk: Vec<String>,
    /// The related table name.
    related_table: String,
    /// The foreign key column on the related table.
    foreign_key: String,
    /// Whether this is a one-to-many (true) or many-to-many (false) relation.
    is_one_to_many: bool,
    /// Join table for many-to-many relations.
    join_table: Option<JoinTableInfo>,
}

/// Information about a join table for many-to-many relations.
#[derive(Debug, Clone)]
pub struct JoinTableInfo {
    /// The join table name.
    pub table_name: String,
    /// Column referencing the parent table.
    pub parent_column: String,
    /// Column referencing the related table.
    pub related_column: String,
}

impl NestedWriteBuilder {
    /// Create a builder for a one-to-many relation.
    pub fn one_to_many(
        parent_table: impl Into<String>,
        parent_pk: Vec<String>,
        related_table: impl Into<String>,
        foreign_key: impl Into<String>,
    ) -> Self {
        Self {
            parent_table: parent_table.into(),
            parent_pk,
            related_table: related_table.into(),
            foreign_key: foreign_key.into(),
            is_one_to_many: true,
            join_table: None,
        }
    }

    /// Create a builder for a many-to-many relation.
    pub fn many_to_many(
        parent_table: impl Into<String>,
        parent_pk: Vec<String>,
        related_table: impl Into<String>,
        join_table: JoinTableInfo,
    ) -> Self {
        Self {
            parent_table: parent_table.into(),
            parent_pk,
            related_table: related_table.into(),
            foreign_key: String::new(), // Not used for many-to-many
            is_one_to_many: false,
            join_table: Some(join_table),
        }
    }

    /// Build SQL for connecting records.
    pub fn build_connect_sql<T: Model>(
        &self,
        parent_id: &FilterValue,
        filters: &[Filter],
    ) -> Vec<(String, Vec<FilterValue>)> {
        let mut statements = Vec::new();

        if self.is_one_to_many {
            // For one-to-many, update the foreign key on related records
            for filter in filters {
                let (where_sql, mut params) = filter.to_sql(1, &crate::dialect::Postgres);
                let sql = format!(
                    "UPDATE {} SET {} = ${} WHERE {}",
                    quote_identifier(&self.related_table),
                    quote_identifier(&self.foreign_key),
                    params.len() + 1,
                    where_sql
                );
                params.push(parent_id.clone());
                statements.push((sql, params));
            }
        } else if let Some(join) = &self.join_table {
            // For many-to-many, insert into join table
            // First, we need to get the IDs of the related records
            for filter in filters {
                let (where_sql, mut params) = filter.to_sql(1, &crate::dialect::Postgres);

                // Get the related record ID (assuming single-column PK for now)
                let select_sql = format!(
                    "SELECT {} FROM {} WHERE {}",
                    quote_identifier(T::PRIMARY_KEY.first().unwrap_or(&"id")),
                    quote_identifier(&self.related_table),
                    where_sql
                );

                // Insert into join table
                let insert_sql = format!(
                    "INSERT INTO {} ({}, {}) SELECT ${}, {} FROM {} WHERE {} ON CONFLICT DO NOTHING",
                    quote_identifier(&join.table_name),
                    quote_identifier(&join.parent_column),
                    quote_identifier(&join.related_column),
                    params.len() + 1,
                    quote_identifier(T::PRIMARY_KEY.first().unwrap_or(&"id")),
                    quote_identifier(&self.related_table),
                    where_sql
                );
                params.push(parent_id.clone());
                statements.push((insert_sql, params));
                // Keep select_sql for potential subquery use
                let _ = select_sql;
            }
        }

        statements
    }

    /// Build SQL for disconnecting records.
    pub fn build_disconnect_sql(
        &self,
        parent_id: &FilterValue,
        filters: &[Filter],
    ) -> Vec<(String, Vec<FilterValue>)> {
        let mut statements = Vec::new();

        if self.is_one_to_many {
            // For one-to-many, set the foreign key to NULL
            for filter in filters {
                let (where_sql, mut params) = filter.to_sql(1, &crate::dialect::Postgres);
                let sql = format!(
                    "UPDATE {} SET {} = NULL WHERE {} AND {} = ${}",
                    quote_identifier(&self.related_table),
                    quote_identifier(&self.foreign_key),
                    where_sql,
                    quote_identifier(&self.foreign_key),
                    params.len() + 1
                );
                params.push(parent_id.clone());
                statements.push((sql, params));
            }
        } else if let Some(join) = &self.join_table {
            // For many-to-many, delete from join table
            for filter in filters {
                let (where_sql, mut params) = filter.to_sql(2, &crate::dialect::Postgres);
                let sql = format!(
                    "DELETE FROM {} WHERE {} = $1 AND {} IN (SELECT id FROM {} WHERE {})",
                    quote_identifier(&join.table_name),
                    quote_identifier(&join.parent_column),
                    quote_identifier(&join.related_column),
                    quote_identifier(&self.related_table),
                    where_sql
                );
                let mut final_params = vec![parent_id.clone()];
                final_params.extend(params);
                params = final_params;
                statements.push((sql, params));
            }
        }

        statements
    }

    /// Build SQL for setting the relation (disconnect all, then connect specified).
    pub fn build_set_sql<T: Model>(
        &self,
        parent_id: &FilterValue,
        filters: &[Filter],
    ) -> Vec<(String, Vec<FilterValue>)> {
        let mut statements = Vec::new();

        // First, disconnect all existing relations
        if self.is_one_to_many {
            let sql = format!(
                "UPDATE {} SET {} = NULL WHERE {} = $1",
                quote_identifier(&self.related_table),
                quote_identifier(&self.foreign_key),
                quote_identifier(&self.foreign_key)
            );
            statements.push((sql, vec![parent_id.clone()]));
        } else if let Some(join) = &self.join_table {
            let sql = format!(
                "DELETE FROM {} WHERE {} = $1",
                quote_identifier(&join.table_name),
                quote_identifier(&join.parent_column)
            );
            statements.push((sql, vec![parent_id.clone()]));
        }

        // Then connect the specified records
        statements.extend(self.build_connect_sql::<T>(parent_id, filters));

        statements
    }

    /// Build SQL for creating nested records.
    pub fn build_create_sql<T: Model>(
        &self,
        parent_id: &FilterValue,
        creates: &[NestedCreateData<T>],
    ) -> Vec<(String, Vec<FilterValue>)> {
        let mut statements = Vec::with_capacity(creates.len());
        let quoted_table = quote_identifier(&self.related_table);

        for create in creates {
            let row_len = create.data.len() + 1;
            let mut columns: Vec<String> = Vec::with_capacity(row_len);
            let mut values: Vec<FilterValue> = Vec::with_capacity(row_len);
            for (k, v) in &create.data {
                columns.push(k.clone());
                values.push(v.clone());
            }

            columns.push(self.foreign_key.clone());
            values.push(parent_id.clone());

            let mut col_list = String::new();
            let mut placeholders = String::new();
            for (i, c) in columns.iter().enumerate() {
                if i > 0 {
                    col_list.push_str(", ");
                    placeholders.push_str(", ");
                }
                col_list.push_str(&quote_identifier(c));
                use std::fmt::Write;
                let _ = write!(placeholders, "${}", i + 1);
            }

            let sql = format!(
                "INSERT INTO {} ({}) VALUES ({}) RETURNING *",
                quoted_table, col_list, placeholders,
            );

            statements.push((sql, values));
        }

        statements
    }

    /// Build SQL for deleting nested records.
    pub fn build_delete_sql(
        &self,
        parent_id: &FilterValue,
        filters: &[Filter],
    ) -> Vec<(String, Vec<FilterValue>)> {
        let mut statements = Vec::new();

        for filter in filters {
            let (where_sql, mut params) = filter.to_sql(1, &crate::dialect::Postgres);
            let sql = format!(
                "DELETE FROM {} WHERE {} AND {} = ${}",
                quote_identifier(&self.related_table),
                where_sql,
                quote_identifier(&self.foreign_key),
                params.len() + 1
            );
            params.push(parent_id.clone());
            statements.push((sql, params));
        }

        statements
    }
}

/// A container for collecting all nested write operations to execute.
#[derive(Debug, Default)]
pub struct NestedWriteOperations {
    /// SQL statements to execute before the main operation.
    pub pre_statements: Vec<(String, Vec<FilterValue>)>,
    /// SQL statements to execute after the main operation.
    pub post_statements: Vec<(String, Vec<FilterValue>)>,
}

impl NestedWriteOperations {
    /// Create a new empty container.
    pub fn new() -> Self {
        Self::default()
    }

    /// Add a pre-operation statement.
    pub fn add_pre(&mut self, sql: String, params: Vec<FilterValue>) {
        self.pre_statements.push((sql, params));
    }

    /// Add a post-operation statement.
    pub fn add_post(&mut self, sql: String, params: Vec<FilterValue>) {
        self.post_statements.push((sql, params));
    }

    /// Extend with statements from another container.
    pub fn extend(&mut self, other: Self) {
        self.pre_statements.extend(other.pre_statements);
        self.post_statements.extend(other.post_statements);
    }

    /// Check if there are any operations.
    pub fn is_empty(&self) -> bool {
        self.pre_statements.is_empty() && self.post_statements.is_empty()
    }

    /// Get total number of statements.
    pub fn len(&self) -> usize {
        self.pre_statements.len() + self.post_statements.len()
    }
}

/// Model-erased nested write op used by `CreateOperation::with(...)`.
///
/// The type-parameterized [`NestedWrite`] above is keyed on the parent
/// model and doesn't compose across heterogeneous child types — a
/// `CreateOperation<E, User>.with(posts_write)` needs to carry child
/// writes for a different model (`Post`) than the parent, so `User`'s
/// `NestedWrite<User>` can't encode them. This sibling enum drops the
/// model type parameter and carries only the runtime metadata the
/// execution path actually needs: the target table, the foreign-key
/// column on that table, and the raw child-column payload.
///
/// Emitted by the codegen's per-relation `create()` / `connect()`
/// helpers on `user::posts::*`. Payloads are a nested
/// `Vec<Vec<(String, FilterValue)>>` rather than a strongly-typed
/// `CreateInput` because the derive path doesn't currently emit a
/// `CreateInput` struct per model — see the task docs for the trade-off
/// and the upgrade path.
#[derive(Debug, Clone)]
pub enum NestedWriteOp {
    /// Create children whose FK column points at the parent's PK.
    ///
    /// `relation` is retained for diagnostics/debugging; the executor
    /// only needs `target_table`, `foreign_key`, and `payload`.
    Create {
        relation: &'static str,
        target_table: &'static str,
        foreign_key: &'static str,
        /// One `Vec<(column, value)>` per child row. The FK column +
        /// parent PK are appended by [`NestedWriteOp::execute`].
        payload: Vec<Vec<(String, FilterValue)>>,
    },
    /// Connect an existing child row by its primary-key value.
    ///
    /// Lowers to
    /// `UPDATE <target_table> SET <foreign_key> = <parent_pk> WHERE <target_pk> = <pk>`
    /// at execute time. The identifier fields are `&'static str` because
    /// they come from codegen-emitted constants on the per-relation
    /// `RelationMeta` / `Model` types — the type itself enforces the
    /// SQL-safety boundary (see `.cursor/rules/sql-safety.mdc`). Only
    /// `parent_pk` and `pk` flow as `$N`-bound parameters.
    Connect {
        relation: &'static str,
        target_table: &'static str,
        foreign_key: &'static str,
        target_pk: &'static str,
        pk: FilterValue,
    },
    /// Disconnect a child row by clearing its FK column to `NULL`.
    ///
    /// Lowers to `UPDATE <target_table> SET <foreign_key> = NULL WHERE <target_pk> = <pk>`.
    /// The child row persists; only the FK is cleared. Use
    /// [`NestedWriteOp::Delete`] to remove the row entirely.
    Disconnect {
        relation: &'static str,
        target_table: &'static str,
        foreign_key: &'static str,
        target_pk: &'static str,
        pk: FilterValue,
    },
    /// Delete a child row by its primary key.
    ///
    /// Lowers to `DELETE FROM <target_table> WHERE <target_pk> = <pk>`.
    /// Returns `QueryError::not_found` when the PK doesn't match any row,
    /// matching the Connect-batch affected-rows contract.
    Delete {
        relation: &'static str,
        target_table: &'static str,
        target_pk: &'static str,
        pk: FilterValue,
    },
    /// Delete many child rows matching a scalar filter, scoped to the
    /// parent's children only.
    ///
    /// Lowers to `DELETE FROM <target_table> WHERE <foreign_key> = <parent_pk> AND <filter>`.
    /// The AND-with-parent-FK clause is a safety bound enforced at SQL
    /// emit time — the user-supplied filter cannot remove rows belonging
    /// to other parents.
    DeleteMany {
        relation: &'static str,
        target_table: &'static str,
        foreign_key: &'static str,
        filter: Filter,
    },
    /// Update a child row by its primary key.
    ///
    /// Lowers to
    /// `UPDATE <target_table> SET <writeop-fragments> WHERE <target_pk> = $1`.
    /// Each entry in `payload` contributes one column assignment whose
    /// shape is determined by the [`crate::inputs::WriteOp`] variant
    /// (plain set, atomic increment/decrement/multiply/divide, or
    /// null-out via Unset). Returns `QueryError::not_found` when the PK
    /// doesn't match any row, mirroring [`NestedWriteOp::Delete`]'s
    /// affected-rows contract.
    Update {
        relation: &'static str,
        target_table: &'static str,
        target_pk: &'static str,
        pk: FilterValue,
        payload: Vec<(String, crate::inputs::WriteOp)>,
    },
    /// Update many child rows matching a filter, scoped to the parent's
    /// children only.
    ///
    /// Lowers to
    /// `UPDATE <target_table> SET <writeop-fragments> WHERE <foreign_key> = $1 AND <filter>`.
    /// The AND-with-parent-FK clause is a safety bound enforced at SQL
    /// emit time — the user-supplied filter cannot reach rows belonging
    /// to other parents.
    UpdateMany {
        relation: &'static str,
        target_table: &'static str,
        foreign_key: &'static str,
        filter: Filter,
        payload: Vec<(String, crate::inputs::WriteOp)>,
    },
    /// Upsert: update if a row matches `pk`, else insert.
    ///
    /// On dialects with native single-statement upsert (Postgres, SQLite,
    /// DuckDB, MySQL), emits one
    /// `INSERT INTO <target_table> (<create_cols + fk>) VALUES (...)
    /// ON CONFLICT (<target_pk>) DO UPDATE SET <update_writeops>`
    /// (or `ON DUPLICATE KEY UPDATE ...` on MySQL). The `pk` field is
    /// unused on this path — conflict detection comes from the inserted
    /// row's PK column, which the codegen guarantees is present in
    /// `create_payload`.
    ///
    /// On MSSQL and CQL, falls back to the two-statement form:
    /// 1. `UPDATE <target_table> SET <update_writeops> WHERE <target_pk> = $1`
    /// 2. If `affected_rows == 0`, `INSERT INTO <target_table>
    ///    (<create_cols + fk>) VALUES (<...>)`.
    ///
    /// **Limitations of the fallback path** (MSSQL/CQL only):
    /// - The `affected_rows == 0` check cannot distinguish "row absent"
    ///   from "row exists but no columns changed" — a UPDATE that hits an
    ///   identical row produces a spurious INSERT attempt and likely a PK
    ///   unique-violation. Wrap the fallback in a transaction (or use a
    ///   single-statement dialect) for strongest semantics.
    /// - There is a TOCTOU race between the UPDATE returning 0 and the
    ///   subsequent INSERT; a concurrent writer can insert the same row
    ///   first.
    ///
    /// Document-store engines (`NotSql` dialect) are rejected at the top
    /// of `execute` with `QueryError::unsupported(...)`.
    ///
    /// **Empty payloads**: an empty `update_payload` on a single-statement
    /// dialect lowers to `ON CONFLICT (...) DO NOTHING` (PG/SQLite/DuckDB)
    /// or `INSERT IGNORE INTO` (MySQL — idempotent no-op).
    /// An empty `create_payload` errors with `QueryError::invalid_input`.
    Upsert {
        relation: &'static str,
        target_table: &'static str,
        foreign_key: &'static str,
        target_pk: &'static str,
        pk: FilterValue,
        create_payload: Vec<(String, FilterValue)>,
        update_payload: Vec<(String, crate::inputs::WriteOp)>,
    },
    /// Connect an existing child row if a `where` filter matches, else
    /// insert a new one with the parent's FK spliced in.
    ///
    /// Two-statement engine-agnostic lowering:
    /// 1. `UPDATE <target_table> SET <foreign_key> = $1 WHERE <filter>`
    ///    (the connect path — points any matching row at the parent).
    /// 2. If `affected_rows == 0`, emit
    ///    `INSERT INTO <target_table> (<create_cols + foreign_key>) VALUES (<...>)`
    ///    (the create path).
    ///
    /// If the filter matches multiple rows, every match has its FK pointed
    /// at the parent — `connect_or_create` is typically used with a unique
    /// where, but this is not enforced at runtime.
    ///
    /// As a safety measure, an empty (`Filter::None`) `where_filter` is
    /// rejected at execute time — without this guard, the UPDATE would
    /// lower to `... WHERE TRUE`, rewriting every row in the table.
    ConnectOrCreate {
        relation: &'static str,
        target_table: &'static str,
        foreign_key: &'static str,
        where_filter: Filter,
        create_payload: Vec<(String, FilterValue)>,
    },
    /// Replace the relation contents — after execution, exactly the
    /// listed child rows are connected to the parent. Rows currently
    /// connected that aren't in `set_pks` get their FK cleared; rows in
    /// `set_pks` that aren't currently connected (or are connected to a
    /// different parent) get their FK pointed at this parent.
    ///
    /// Two-statement engine-agnostic lowering:
    /// 1. `UPDATE <target_table> SET <foreign_key> = NULL WHERE <foreign_key> = $parent AND <target_pk> NOT IN (set_pks)`
    /// 2. `UPDATE <target_table> SET <foreign_key> = $parent WHERE <target_pk> IN (set_pks)`
    ///
    /// When `set_pks` is empty, step 1's `NOT IN ()` is invalid SQL —
    /// the executor special-cases this to `UPDATE <child> SET <fk> = NULL
    /// WHERE <fk> = $parent` (no NOT IN clause), then skips step 2.
    ///
    /// `set:` claims rows for this parent regardless of who they belonged
    /// to before — pre-existing FK values get overwritten. This matches
    /// Prisma's relation-replacement semantics.
    Set {
        relation: &'static str,
        target_table: &'static str,
        foreign_key: &'static str,
        target_pk: &'static str,
        set_pks: Vec<FilterValue>,
    },
}

/// Shared SET-clause builder for the `Upsert` single-statement and
/// two-statement fallback paths. `start_ph` lets the caller position
/// placeholders after any preceding INSERT values; PG-family dialects
/// use this index numerically, MySQL ignores it (`?` placeholders are
/// positional via param push order).
///
/// `Unset` ops emit `col = NULL` and consume no placeholder slot.
fn build_writeop_set_clause(
    payload: &[(String, crate::inputs::WriteOp)],
    dialect: &dyn crate::dialect::SqlDialect,
    start_ph: usize,
) -> (String, Vec<FilterValue>) {
    let mut fragments: Vec<String> = Vec::with_capacity(payload.len());
    let mut params: Vec<FilterValue> = Vec::with_capacity(payload.len());
    let mut next_ph = start_ph;
    for (col, op) in payload {
        let (frag, maybe_val) =
            op.to_set_fragment(&dialect.quote_ident(col), &dialect.placeholder(next_ph));
        fragments.push(frag);
        if let Some(val) = maybe_val {
            params.push(val);
            next_ph += 1;
        }
    }
    (fragments.join(", "), params)
}

impl NestedWriteOp {
    /// Execute this nested write inside `engine`, using `parent_pk`
    /// as the foreign-key value to splice into each child row.
    ///
    /// For `Create`, this emits one `INSERT INTO <target_table> (...)`
    /// per child, appending the FK column + parent PK to whatever
    /// columns/values the caller supplied.
    pub async fn execute<E>(self, engine: &E, parent_pk: &FilterValue) -> QueryResult<()>
    where
        E: QueryEngine,
    {
        match self {
            NestedWriteOp::Connect {
                relation: _,
                target_table,
                foreign_key,
                target_pk,
                pk,
            } => {
                let dialect = engine.dialect();
                let sql = format!(
                    "UPDATE {} SET {} = {} WHERE {} = {}",
                    dialect.quote_ident(target_table),
                    dialect.quote_ident(foreign_key),
                    dialect.placeholder(1),
                    dialect.quote_ident(target_pk),
                    dialect.placeholder(2),
                );
                engine
                    .execute_raw(&sql, vec![parent_pk.clone(), pk])
                    .await?;
                Ok(())
            }
            NestedWriteOp::Disconnect {
                relation: _,
                target_table,
                foreign_key,
                target_pk,
                pk,
            } => {
                let dialect = engine.dialect();
                let sql = format!(
                    "UPDATE {} SET {} = NULL WHERE {} = {}",
                    dialect.quote_ident(target_table),
                    dialect.quote_ident(foreign_key),
                    dialect.quote_ident(target_pk),
                    dialect.placeholder(1),
                );
                engine.execute_raw(&sql, vec![pk]).await?;
                Ok(())
            }
            NestedWriteOp::Delete {
                relation: _,
                target_table,
                target_pk,
                pk,
            } => {
                let dialect = engine.dialect();
                let sql = format!(
                    "DELETE FROM {} WHERE {} = {}",
                    dialect.quote_ident(target_table),
                    dialect.quote_ident(target_pk),
                    dialect.placeholder(1),
                );
                let affected = engine.execute_raw(&sql, vec![pk]).await?;
                if affected != 1 {
                    return Err(crate::error::QueryError::not_found(target_table)
                        .with_context("Nested Delete by PK"));
                }
                Ok(())
            }
            NestedWriteOp::DeleteMany {
                relation: _,
                target_table,
                foreign_key,
                filter,
            } => {
                let dialect = engine.dialect();
                let is_unconstrained = matches!(filter, Filter::None);
                let sql = if is_unconstrained {
                    format!(
                        "DELETE FROM {} WHERE {} = {}",
                        dialect.quote_ident(target_table),
                        dialect.quote_ident(foreign_key),
                        dialect.placeholder(1),
                    )
                } else {
                    let (filter_sql, params_tail) = filter.to_sql(2, &crate::dialect::Postgres);
                    let sql = format!(
                        "DELETE FROM {} WHERE {} = {} AND ({})",
                        dialect.quote_ident(target_table),
                        dialect.quote_ident(foreign_key),
                        dialect.placeholder(1),
                        filter_sql,
                    );
                    let mut params = Vec::with_capacity(params_tail.len() + 1);
                    params.push(parent_pk.clone());
                    params.extend(params_tail);
                    return engine.execute_raw(&sql, params).await.map(|_| ());
                };
                engine.execute_raw(&sql, vec![parent_pk.clone()]).await?;
                Ok(())
            }
            NestedWriteOp::Update {
                relation: _,
                target_table,
                target_pk,
                pk,
                payload,
            } => {
                if payload.is_empty() {
                    return Ok(());
                }
                let dialect = engine.dialect();
                let (set_text, mut update_params) = build_writeop_set_clause(&payload, dialect, 1);
                let next_placeholder = update_params.len() + 1;
                update_params.push(pk);
                let sql = format!(
                    "UPDATE {} SET {} WHERE {} = {}",
                    dialect.quote_ident(target_table),
                    set_text,
                    dialect.quote_ident(target_pk),
                    dialect.placeholder(next_placeholder),
                );
                let affected = engine.execute_raw(&sql, update_params).await?;
                if affected != 1 {
                    return Err(crate::error::QueryError::not_found(target_table)
                        .with_context("Nested Update by PK"));
                }
                Ok(())
            }
            NestedWriteOp::UpdateMany {
                relation: _,
                target_table,
                foreign_key,
                filter,
                payload,
            } => {
                if payload.is_empty() {
                    return Ok(());
                }
                let dialect = engine.dialect();
                let (set_text, mut params) = build_writeop_set_clause(&payload, dialect, 1);
                let fk_placeholder_idx = params.len() + 1;
                let fk_placeholder = dialect.placeholder(fk_placeholder_idx);
                let next_placeholder = fk_placeholder_idx + 1;
                params.push(parent_pk.clone());

                let is_unconstrained = matches!(filter, Filter::None);
                let sql = if is_unconstrained {
                    format!(
                        "UPDATE {} SET {} WHERE {} = {}",
                        dialect.quote_ident(target_table),
                        set_text,
                        dialect.quote_ident(foreign_key),
                        fk_placeholder,
                    )
                } else {
                    let (filter_sql, filter_params) =
                        filter.to_sql(next_placeholder, &crate::dialect::Postgres);
                    params.extend(filter_params);
                    format!(
                        "UPDATE {} SET {} WHERE {} = {} AND ({})",
                        dialect.quote_ident(target_table),
                        set_text,
                        dialect.quote_ident(foreign_key),
                        fk_placeholder,
                        filter_sql,
                    )
                };
                engine.execute_raw(&sql, params).await?;
                Ok(())
            }
            NestedWriteOp::Upsert {
                relation: _,
                target_table,
                foreign_key,
                target_pk,
                pk,
                create_payload,
                update_payload,
            } => {
                let dialect = engine.dialect();

                // Guard: document-store engines (NotSql) panic on any SQL
                // emission helper. Short-circuit before touching the dialect.
                if !dialect.supports_upsert() {
                    return Err(crate::error::QueryError::unsupported(format!(
                        "Nested Upsert is not supported by the `{}` engine",
                        std::any::type_name::<dyn crate::dialect::SqlDialect>()
                    )));
                }

                // Guard: an upsert with no payloads is a no-op.
                if update_payload.is_empty() && create_payload.is_empty() {
                    return Ok(());
                }

                // Guard: create_payload must not be empty — we can't INSERT
                // a row with no columns.
                if create_payload.is_empty() {
                    return Err(crate::error::QueryError::invalid_input(
                        "create_payload",
                        "Nested Upsert requires at least one create column when no row to update",
                    ));
                }

                // Probe the dialect for single-statement upsert support by
                // checking whether upsert_clause returns a non-empty string.
                //
                // For the normal path (non-empty update_payload): build the
                // SET fragment with placeholders positioned AFTER the INSERT's
                // column values (insert occupies $1..$N where N =
                // create_payload.len() + 1 for the FK).
                //
                // On PG-family dialects the `start_ph` arg positions SET-clause
                // placeholders after the INSERT VALUES placeholders ($N+1, $N+2, ...).
                // On MySQL the placeholder text is always `?` — the SET-vs-VALUES split
                // is enforced solely by the param-push order: INSERT values are pushed
                // first below, then SET params via `values.extend(probe_set_params)`.
                let insert_arity = create_payload.len() + 1; // cols + FK
                let (probe_set_text, probe_set_params) =
                    build_writeop_set_clause(&update_payload, dialect, insert_arity + 1);

                // Builds columns + values + placeholders + quoted_cols from
                // create_payload + foreign_key + parent_pk. Used by both the
                // single-statement and two-statement INSERT phases below.
                let build_insert_columns_and_values = || {
                    let mut columns: Vec<String> =
                        create_payload.iter().map(|(c, _)| c.clone()).collect();
                    let mut values: Vec<FilterValue> =
                        create_payload.iter().map(|(_, v)| v.clone()).collect();
                    columns.push(foreign_key.to_string());
                    values.push(parent_pk.clone());
                    let placeholders: Vec<String> =
                        (1..=values.len()).map(|i| dialect.placeholder(i)).collect();
                    let quoted_cols: Vec<String> =
                        columns.iter().map(|c| dialect.quote_ident(c)).collect();
                    (columns, values, placeholders, quoted_cols)
                };

                // Pass raw (unquoted) target_pk — upsert_clause implementations
                // are responsible for quoting identifiers internally.
                let conflict_cols = [target_pk];
                let upsert_clause_text = dialect.upsert_clause(&conflict_cols, &probe_set_text);

                if !upsert_clause_text.is_empty() {
                    // Single-statement path:
                    //   INSERT INTO child (cols + fk) VALUES ($1..$N) ON CONFLICT (...) DO UPDATE SET ...
                    //   or (empty update_payload): INSERT … ON CONFLICT DO NOTHING / INSERT IGNORE
                    let (_, mut values, placeholders, quoted_cols) =
                        build_insert_columns_and_values();

                    // Drop the `pk` value — the single-statement form never
                    // references it; the conflict target is derived from the
                    // inserted row's PK column (which the codegen guarantees
                    // is present when create_payload is populated by the macro).
                    let _ = pk;

                    let effective_upsert_clause = if update_payload.is_empty() {
                        // Pure-insert semantics: collapse to conditional INSERT.
                        // Use upsert_do_nothing_clause for dialect-specific DO NOTHING syntax.
                        // MySQL returns the idempotent self-assign form; PG/SQLite/DuckDB
                        // return ON CONFLICT (...) DO NOTHING.
                        let do_nothing = dialect.upsert_do_nothing_clause(&conflict_cols);
                        if do_nothing.is_empty() {
                            // Fallback dialect (MSSQL/CQL) with empty upsert_do_nothing_clause
                            // but non-empty upsert_clause_text: very rare. Treat as no-op.
                            return Ok(());
                        }
                        do_nothing
                    } else {
                        values.extend(probe_set_params);
                        upsert_clause_text
                    };

                    let sql = format!(
                        "INSERT INTO {} ({}) VALUES ({}){}",
                        dialect.quote_ident(target_table),
                        quoted_cols.join(", "),
                        placeholders.join(", "),
                        effective_upsert_clause,
                    );
                    engine.execute_raw(&sql, values).await?;
                    return Ok(());
                }

                // Two-statement fallback for dialects without native upsert syntax
                // (MSSQL, CQL). NotSql engines short-circuit above with QueryError::unsupported.
                //
                // TODO(upsert-toctou): `affected_rows == 0` cannot distinguish
                // "no row matched" from "row matched but no columns changed"
                // (MSSQL `@@ROWCOUNT`, CQL row-count semantics). A no-op UPDATE
                // would incorrectly trigger the INSERT, producing a PK unique
                // violation. Wrapping in an explicit transaction requires plumbing
                // not yet available here; tracked for a follow-up PR.
                if update_payload.is_empty() {
                    // Pure-insert semantics on fallback path: skip the UPDATE
                    // entirely and emit a bare INSERT. If the row already exists
                    // the engine will surface a PK/unique violation, which is
                    // the correct behaviour for an insert-or-fail path on dialects
                    // without native upsert syntax.
                    let (_, values, placeholders, quoted_cols) = build_insert_columns_and_values();
                    let insert_sql = format!(
                        "INSERT INTO {} ({}) VALUES ({})",
                        dialect.quote_ident(target_table),
                        quoted_cols.join(", "),
                        placeholders.join(", "),
                    );
                    engine.execute_raw(&insert_sql, values).await?;
                    return Ok(());
                }

                // Phase 1: attempt UPDATE.
                let (set_text, mut update_params) =
                    build_writeop_set_clause(&update_payload, dialect, 1);
                let next_placeholder = update_params.len() + 1;
                update_params.push(pk.clone());
                let update_sql = format!(
                    "UPDATE {} SET {} WHERE {} = {}",
                    dialect.quote_ident(target_table),
                    set_text,
                    dialect.quote_ident(target_pk),
                    dialect.placeholder(next_placeholder),
                );
                let affected = engine.execute_raw(&update_sql, update_params).await?;
                if affected > 0 {
                    return Ok(());
                }
                // Phase 2: row didn't exist — INSERT it with the FK spliced in.
                let (_, values, placeholders, quoted_cols) = build_insert_columns_and_values();
                let insert_sql = format!(
                    "INSERT INTO {} ({}) VALUES ({})",
                    dialect.quote_ident(target_table),
                    quoted_cols.join(", "),
                    placeholders.join(", "),
                );
                engine.execute_raw(&insert_sql, values).await?;
                Ok(())
            }
            NestedWriteOp::ConnectOrCreate {
                relation: _,
                target_table,
                foreign_key,
                where_filter,
                create_payload,
            } => {
                // Safety: reject an empty (`Filter::None`) where. Without
                // this guard the UPDATE would lower to `... WHERE TRUE`
                // (per `Filter::None::to_sql`), rewriting every row in
                // the child table. `connect_or_create` semantically
                // requires a unique-where lookup; an empty where is a
                // user error, not an "always match every row" command.
                if matches!(where_filter, Filter::None) {
                    return Err(crate::error::QueryError::not_found(target_table).with_context(
                        "Nested ConnectOrCreate: empty `where` block would match every row; supply a unique filter",
                    ));
                }
                let dialect = engine.dialect();
                // Phase 1: attempt UPDATE to connect existing row(s).
                let (filter_sql, filter_params) = where_filter.to_sql(2, &crate::dialect::Postgres);
                let mut update_params: Vec<FilterValue> =
                    Vec::with_capacity(filter_params.len() + 1);
                update_params.push(parent_pk.clone());
                update_params.extend(filter_params);
                let update_sql = format!(
                    "UPDATE {} SET {} = {} WHERE {}",
                    dialect.quote_ident(target_table),
                    dialect.quote_ident(foreign_key),
                    dialect.placeholder(1),
                    filter_sql,
                );
                let affected = engine.execute_raw(&update_sql, update_params).await?;
                if affected > 0 {
                    return Ok(());
                }
                // Phase 2: no row matched — INSERT with FK spliced in.
                if create_payload.is_empty() {
                    return Err(
                        crate::error::QueryError::not_found(target_table).with_context(
                            "Nested ConnectOrCreate: no match and create payload empty",
                        ),
                    );
                }
                let mut columns: Vec<String> =
                    create_payload.iter().map(|(c, _)| c.clone()).collect();
                let mut values: Vec<FilterValue> =
                    create_payload.into_iter().map(|(_, v)| v).collect();
                columns.push(foreign_key.to_string());
                values.push(parent_pk.clone());
                let placeholders: Vec<String> =
                    (1..=values.len()).map(|i| dialect.placeholder(i)).collect();
                let quoted_cols: Vec<String> =
                    columns.iter().map(|c| dialect.quote_ident(c)).collect();
                let insert_sql = format!(
                    "INSERT INTO {} ({}) VALUES ({})",
                    dialect.quote_ident(target_table),
                    quoted_cols.join(", "),
                    placeholders.join(", "),
                );
                engine.execute_raw(&insert_sql, values).await?;
                Ok(())
            }
            NestedWriteOp::Create {
                relation: _,
                target_table,
                foreign_key,
                payload,
            } => {
                if payload.is_empty() {
                    return Ok(());
                }

                let dialect = engine.dialect();

                // All rows in a single `Create` op share the same column
                // set (codegen guarantee). Derive columns from the first
                // row, then append the FK column once. Each row
                // contributes its values + the parent PK.
                let first = &payload[0];
                let mut columns: Vec<String> = first.iter().map(|(c, _)| c.clone()).collect();
                columns.push(foreign_key.to_string());
                let cols_per_row = columns.len();

                let quoted_cols: Vec<String> =
                    columns.iter().map(|c| dialect.quote_ident(c)).collect();

                let mut values: Vec<FilterValue> = Vec::with_capacity(payload.len() * cols_per_row);
                let mut row_placeholders: Vec<String> = Vec::with_capacity(payload.len());
                let mut next_placeholder = 1usize;

                for child in payload {
                    let mut row_phs: Vec<String> = Vec::with_capacity(cols_per_row);
                    for (_, v) in child {
                        values.push(v);
                        row_phs.push(dialect.placeholder(next_placeholder));
                        next_placeholder += 1;
                    }
                    values.push(parent_pk.clone());
                    row_phs.push(dialect.placeholder(next_placeholder));
                    next_placeholder += 1;
                    row_placeholders.push(format!("({})", row_phs.join(", ")));
                }

                // NOTE: Combining all rows into a single multi-VALUES
                // INSERT means any constraint failure rolls back the
                // entire batch, not just the failing row. This matches
                // typical Prisma semantics for nested writes.
                let sql = format!(
                    "INSERT INTO {} ({}) VALUES {}",
                    dialect.quote_ident(target_table),
                    quoted_cols.join(", "),
                    row_placeholders.join(", "),
                );

                engine.execute_raw(&sql, values).await?;
                Ok(())
            }
            NestedWriteOp::Set {
                relation: _,
                target_table,
                foreign_key,
                target_pk,
                set_pks,
            } => {
                let dialect = engine.dialect();

                // Phase 1: disconnect current children not in set_pks.
                if set_pks.is_empty() {
                    // No NOT IN clause needed — clear every child of this parent.
                    let sql = format!(
                        "UPDATE {} SET {} = NULL WHERE {} = {}",
                        dialect.quote_ident(target_table),
                        dialect.quote_ident(foreign_key),
                        dialect.quote_ident(foreign_key),
                        dialect.placeholder(1),
                    );
                    engine.execute_raw(&sql, vec![parent_pk.clone()]).await?;
                    return Ok(());
                }
                // set_pks is non-empty — emit disconnect with NOT IN clause + connect.
                let mut disconnect_params: Vec<FilterValue> = Vec::with_capacity(set_pks.len() + 1);
                disconnect_params.push(parent_pk.clone());
                let mut not_in_placeholders: Vec<String> = Vec::with_capacity(set_pks.len());
                for (i, pk) in set_pks.iter().enumerate() {
                    disconnect_params.push(pk.clone());
                    not_in_placeholders.push(dialect.placeholder(i + 2));
                }
                let disconnect_sql = format!(
                    "UPDATE {} SET {} = NULL WHERE {} = {} AND {} NOT IN ({})",
                    dialect.quote_ident(target_table),
                    dialect.quote_ident(foreign_key),
                    dialect.quote_ident(foreign_key),
                    dialect.placeholder(1),
                    dialect.quote_ident(target_pk),
                    not_in_placeholders.join(", "),
                );
                engine
                    .execute_raw(&disconnect_sql, disconnect_params)
                    .await?;

                // Phase 2: connect every row in set_pks (idempotent for already-connected).
                let mut connect_params: Vec<FilterValue> = Vec::with_capacity(set_pks.len() + 1);
                connect_params.push(parent_pk.clone());
                let mut in_placeholders: Vec<String> = Vec::with_capacity(set_pks.len());
                for (i, pk) in set_pks.iter().enumerate() {
                    connect_params.push(pk.clone());
                    in_placeholders.push(dialect.placeholder(i + 2));
                }
                let connect_sql = format!(
                    "UPDATE {} SET {} = {} WHERE {} IN ({})",
                    dialect.quote_ident(target_table),
                    dialect.quote_ident(foreign_key),
                    dialect.placeholder(1),
                    dialect.quote_ident(target_pk),
                    in_placeholders.join(", "),
                );
                engine.execute_raw(&connect_sql, connect_params).await?;
                Ok(())
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::sync::{Arc, Mutex};

    use crate::error::QueryError;
    use crate::traits::BoxFuture;

    /// Captured (sql, params) entries from the mock engine.
    type StatementLog = Arc<Mutex<Vec<(String, Vec<FilterValue>)>>>;

    #[derive(Clone, Copy)]
    enum DialectKind {
        Postgres,
        Mssql,
        NotSql,
    }

    /// Recording mock engine for [`NestedWriteOp::execute`] tests.
    ///
    /// Captures the (sql, params) of every [`QueryEngine::execute_raw`]
    /// call so tests can assert the lowered shape. Returns 1 from
    /// `execute_raw` by default; tests that need to exercise the
    /// zero-affected-rows path (e.g. upsert's insert phase) can supply a
    /// sequence of affected-row counts via [`RecordingEngine::with_affected`].
    #[derive(Clone)]
    struct RecordingEngine {
        recorded: StatementLog,
        affected: Arc<Mutex<Vec<u64>>>,
        dialect_kind: DialectKind,
    }

    impl RecordingEngine {
        fn new() -> Self {
            Self {
                recorded: Arc::new(Mutex::new(Vec::new())),
                affected: Arc::new(Mutex::new(Vec::new())),
                dialect_kind: DialectKind::Postgres,
            }
        }

        /// Build an engine that returns each entry of `seq` from successive
        /// `execute_raw` calls, in order. Once exhausted, falls back to 1.
        fn with_affected(seq: Vec<u64>) -> Self {
            // Stored in reverse so we can pop in O(1).
            let mut rev = seq;
            rev.reverse();
            Self {
                recorded: Arc::new(Mutex::new(Vec::new())),
                affected: Arc::new(Mutex::new(rev)),
                dialect_kind: DialectKind::Postgres,
            }
        }

        fn mssql() -> Self {
            Self {
                dialect_kind: DialectKind::Mssql,
                ..Self::new()
            }
        }

        fn mssql_with_affected(seq: Vec<u64>) -> Self {
            Self {
                dialect_kind: DialectKind::Mssql,
                ..Self::with_affected(seq)
            }
        }

        fn notsql() -> Self {
            Self {
                dialect_kind: DialectKind::NotSql,
                ..Self::new()
            }
        }

        fn statements(&self) -> Vec<(String, Vec<FilterValue>)> {
            self.recorded.lock().unwrap().clone()
        }
    }

    impl crate::traits::QueryEngine for RecordingEngine {
        fn dialect(&self) -> &dyn crate::dialect::SqlDialect {
            match self.dialect_kind {
                DialectKind::Postgres => &crate::dialect::Postgres,
                DialectKind::Mssql => &crate::dialect::Mssql,
                DialectKind::NotSql => &crate::dialect::NotSql,
            }
        }

        fn query_many<T: Model + crate::row::FromRow + Send + 'static>(
            &self,
            _sql: &str,
            _params: Vec<FilterValue>,
        ) -> BoxFuture<'_, QueryResult<Vec<T>>> {
            Box::pin(async { Ok(Vec::new()) })
        }

        fn query_one<T: Model + crate::row::FromRow + Send + 'static>(
            &self,
            _sql: &str,
            _params: Vec<FilterValue>,
        ) -> BoxFuture<'_, QueryResult<T>> {
            Box::pin(async { Err(QueryError::not_found("test")) })
        }

        fn query_optional<T: Model + crate::row::FromRow + Send + 'static>(
            &self,
            _sql: &str,
            _params: Vec<FilterValue>,
        ) -> BoxFuture<'_, QueryResult<Option<T>>> {
            Box::pin(async { Ok(None) })
        }

        fn execute_insert<T: Model + crate::row::FromRow + Send + 'static>(
            &self,
            _sql: &str,
            _params: Vec<FilterValue>,
        ) -> BoxFuture<'_, QueryResult<T>> {
            Box::pin(async { Err(QueryError::not_found("test")) })
        }

        fn execute_update<T: Model + crate::row::FromRow + Send + 'static>(
            &self,
            _sql: &str,
            _params: Vec<FilterValue>,
        ) -> BoxFuture<'_, QueryResult<Vec<T>>> {
            Box::pin(async { Ok(Vec::new()) })
        }

        fn execute_delete(
            &self,
            _sql: &str,
            _params: Vec<FilterValue>,
        ) -> BoxFuture<'_, QueryResult<u64>> {
            Box::pin(async { Ok(0) })
        }

        fn execute_raw(
            &self,
            sql: &str,
            params: Vec<FilterValue>,
        ) -> BoxFuture<'_, QueryResult<u64>> {
            let recorded = self.recorded.clone();
            let affected = self.affected.clone();
            let sql = sql.to_string();
            Box::pin(async move {
                recorded.lock().unwrap().push((sql, params));
                let next = affected.lock().unwrap().pop().unwrap_or(1);
                Ok(next)
            })
        }

        fn count(&self, _sql: &str, _params: Vec<FilterValue>) -> BoxFuture<'_, QueryResult<u64>> {
            Box::pin(async { Ok(0) })
        }
    }

    struct TestModel;

    impl Model for TestModel {
        const MODEL_NAME: &'static str = "Post";
        const TABLE_NAME: &'static str = "posts";
        const PRIMARY_KEY: &'static [&'static str] = &["id"];
        const COLUMNS: &'static [&'static str] = &["id", "title", "user_id"];
    }

    struct TagModel;

    impl Model for TagModel {
        const MODEL_NAME: &'static str = "Tag";
        const TABLE_NAME: &'static str = "tags";
        const PRIMARY_KEY: &'static [&'static str] = &["id"];
        const COLUMNS: &'static [&'static str] = &["id", "name"];
    }

    #[test]
    fn test_nested_create_data() {
        let data: NestedCreateData<TestModel> =
            NestedCreateData::from_pairs([("title", FilterValue::String("Test Post".to_string()))]);

        assert_eq!(data.data.len(), 1);
        assert_eq!(data.data[0].0, "title");
    }

    #[test]
    fn test_nested_write_create() {
        let data: NestedCreateData<TestModel> =
            NestedCreateData::from_pairs([("title", FilterValue::String("Test Post".to_string()))]);

        let write: NestedWrite<TestModel> = NestedWrite::create(data);

        match write {
            NestedWrite::Create(creates) => assert_eq!(creates.len(), 1),
            _ => panic!("Expected Create variant"),
        }
    }

    #[test]
    fn test_nested_write_connect() {
        let write: NestedWrite<TestModel> = NestedWrite::connect(vec![
            Filter::Equals("id".into(), FilterValue::Int(1)),
            Filter::Equals("id".into(), FilterValue::Int(2)),
        ]);

        match write {
            NestedWrite::Connect(filters) => assert_eq!(filters.len(), 2),
            _ => panic!("Expected Connect variant"),
        }
    }

    #[test]
    fn test_nested_write_disconnect() {
        let write: NestedWrite<TestModel> =
            NestedWrite::disconnect_one(Filter::Equals("id".into(), FilterValue::Int(1)));

        match write {
            NestedWrite::Disconnect(filters) => assert_eq!(filters.len(), 1),
            _ => panic!("Expected Disconnect variant"),
        }
    }

    #[test]
    fn test_nested_write_set() {
        let write: NestedWrite<TestModel> =
            NestedWrite::set(vec![Filter::Equals("id".into(), FilterValue::Int(1))]);

        match write {
            NestedWrite::Set(filters) => assert_eq!(filters.len(), 1),
            _ => panic!("Expected Set variant"),
        }
    }

    #[test]
    fn test_builder_one_to_many_connect() {
        let builder =
            NestedWriteBuilder::one_to_many("users", vec!["id".to_string()], "posts", "user_id");

        let parent_id = FilterValue::Int(1);
        let filters = vec![Filter::Equals("id".into(), FilterValue::Int(10))];

        let statements = builder.build_connect_sql::<TestModel>(&parent_id, &filters);

        assert_eq!(statements.len(), 1);
        let (sql, params) = &statements[0];
        assert!(sql.contains("UPDATE"));
        assert!(sql.contains("posts"));
        assert!(sql.contains("user_id"));
        assert_eq!(params.len(), 2);
    }

    #[test]
    fn test_builder_one_to_many_disconnect() {
        let builder =
            NestedWriteBuilder::one_to_many("users", vec!["id".to_string()], "posts", "user_id");

        let parent_id = FilterValue::Int(1);
        let filters = vec![Filter::Equals("id".into(), FilterValue::Int(10))];

        let statements = builder.build_disconnect_sql(&parent_id, &filters);

        assert_eq!(statements.len(), 1);
        let (sql, params) = &statements[0];
        assert!(sql.contains("UPDATE"));
        assert!(sql.contains("SET"));
        assert!(sql.contains("NULL"));
        assert_eq!(params.len(), 2);
    }

    #[test]
    fn test_builder_many_to_many_connect() {
        let builder = NestedWriteBuilder::many_to_many(
            "posts",
            vec!["id".to_string()],
            "tags",
            JoinTableInfo {
                table_name: "post_tags".to_string(),
                parent_column: "post_id".to_string(),
                related_column: "tag_id".to_string(),
            },
        );

        let parent_id = FilterValue::Int(1);
        let filters = vec![Filter::Equals("id".into(), FilterValue::Int(10))];

        let statements = builder.build_connect_sql::<TagModel>(&parent_id, &filters);

        assert_eq!(statements.len(), 1);
        let (sql, _params) = &statements[0];
        assert!(sql.contains("INSERT INTO"));
        assert!(sql.contains("post_tags"));
        assert!(sql.contains("ON CONFLICT DO NOTHING"));
    }

    #[test]
    fn test_builder_create() {
        let builder =
            NestedWriteBuilder::one_to_many("users", vec!["id".to_string()], "posts", "user_id");

        let parent_id = FilterValue::Int(1);
        let creates = vec![NestedCreateData::<TestModel>::from_pairs([(
            "title",
            FilterValue::String("New Post".to_string()),
        )])];

        let statements = builder.build_create_sql::<TestModel>(&parent_id, &creates);

        assert_eq!(statements.len(), 1);
        let (sql, params) = &statements[0];
        assert!(sql.contains("INSERT INTO"));
        assert!(sql.contains("posts"));
        assert!(sql.contains("RETURNING"));
        assert_eq!(params.len(), 2); // title + user_id
    }

    #[test]
    fn test_builder_set() {
        let builder =
            NestedWriteBuilder::one_to_many("users", vec!["id".to_string()], "posts", "user_id");

        let parent_id = FilterValue::Int(1);
        let filters = vec![Filter::Equals("id".into(), FilterValue::Int(10))];

        let statements = builder.build_set_sql::<TestModel>(&parent_id, &filters);

        // Should have disconnect all + connect statements
        assert!(statements.len() >= 2);

        // First statement should disconnect all
        let (first_sql, _) = &statements[0];
        assert!(first_sql.contains("UPDATE"));
        assert!(first_sql.contains("NULL"));
    }

    #[test]
    fn test_nested_write_operations() {
        let mut ops = NestedWriteOperations::new();
        assert!(ops.is_empty());
        assert_eq!(ops.len(), 0);

        ops.add_pre("SELECT 1".to_string(), vec![]);
        ops.add_post("SELECT 2".to_string(), vec![]);

        assert!(!ops.is_empty());
        assert_eq!(ops.len(), 2);
    }

    #[test]
    fn test_nested_create_or_connect() {
        let create_data: NestedCreateData<TestModel> =
            NestedCreateData::from_pairs([("title", FilterValue::String("New Post".to_string()))]);

        let create_or_connect = NestedCreateOrConnectData::new(
            Filter::Equals("title".into(), FilterValue::String("Existing".to_string())),
            create_data,
        );

        assert!(matches!(create_or_connect.filter, Filter::Equals(..)));
        assert_eq!(create_or_connect.create.data.len(), 1);
    }

    #[test]
    fn test_nested_update_data() {
        let update: NestedUpdateData<TestModel> = NestedUpdateData::from_pairs(
            Filter::Equals("id".into(), FilterValue::Int(1)),
            [("title", FilterValue::String("Updated".to_string()))],
        );

        assert!(matches!(update.filter, Filter::Equals(..)));
        assert_eq!(update.data.len(), 1);
        assert_eq!(update.data[0].0, "title");
    }

    #[tokio::test]
    async fn nested_op_connect_emits_update_set_where() {
        let engine = RecordingEngine::new();
        let op = NestedWriteOp::Connect {
            relation: "posts",
            target_table: "posts",
            foreign_key: "author_id",
            target_pk: "id",
            pk: FilterValue::Int(42),
        };
        let parent_pk = FilterValue::Int(7);
        op.execute(&engine, &parent_pk).await.unwrap();

        let stmts = engine.statements();
        assert_eq!(stmts.len(), 1, "expected one UPDATE statement");
        let (sql, params) = &stmts[0];
        // Postgres dialect quotes idents with double quotes.
        assert!(sql.contains("UPDATE"), "got: {sql}");
        assert!(sql.contains("posts"), "got: {sql}");
        assert!(sql.contains("author_id"), "got: {sql}");
        assert!(sql.contains("SET"), "got: {sql}");
        assert!(sql.contains("WHERE"), "got: {sql}");
        assert!(sql.contains("$1"), "got: {sql}");
        assert!(sql.contains("$2"), "got: {sql}");
        assert_eq!(params, &vec![FilterValue::Int(7), FilterValue::Int(42)]);
    }

    #[tokio::test]
    async fn nested_op_delete_many_with_filter_emits_fk_and_filter_clause() {
        let engine = RecordingEngine::new();
        let op = NestedWriteOp::DeleteMany {
            relation: "posts",
            target_table: "posts",
            foreign_key: "author_id",
            filter: Filter::Equals("published".into(), FilterValue::Bool(false)),
        };
        op.execute(&engine, &FilterValue::Int(7)).await.unwrap();

        let stmts = engine.statements();
        assert_eq!(stmts.len(), 1);
        let (sql, params) = &stmts[0];
        assert!(sql.contains("DELETE FROM"), "got: {sql}");
        assert!(sql.contains("author_id"), "got: {sql}");
        assert!(sql.contains("$1"), "got: {sql}");
        assert!(sql.contains("AND"), "got: {sql}");
        assert!(sql.contains("published"), "got: {sql}");
        assert_eq!(params.len(), 2);
        assert!(matches!(params[0], FilterValue::Int(7)));
        assert!(matches!(params[1], FilterValue::Bool(false)));
    }

    #[tokio::test]
    async fn nested_op_delete_many_with_empty_filter_omits_and_clause() {
        let engine = RecordingEngine::new();
        let op = NestedWriteOp::DeleteMany {
            relation: "posts",
            target_table: "posts",
            foreign_key: "author_id",
            filter: Filter::None,
        };
        op.execute(&engine, &FilterValue::Int(7)).await.unwrap();

        let stmts = engine.statements();
        let (sql, params) = &stmts[0];
        assert!(sql.contains("DELETE FROM"), "got: {sql}");
        assert!(
            !sql.contains("AND"),
            "should omit AND when filter empty: {sql}"
        );
        assert_eq!(params.len(), 1);
    }

    #[tokio::test]
    async fn nested_op_delete_emits_delete_where_pk() {
        let engine = RecordingEngine::new();
        let op = NestedWriteOp::Delete {
            relation: "posts",
            target_table: "posts",
            target_pk: "id",
            pk: FilterValue::Int(42),
        };
        op.execute(&engine, &FilterValue::Int(7)).await.unwrap();

        let stmts = engine.statements();
        assert_eq!(stmts.len(), 1);
        let (sql, params) = &stmts[0];
        assert!(sql.contains("DELETE FROM"), "got: {sql}");
        assert!(sql.contains("posts"), "got: {sql}");
        assert!(sql.contains("WHERE"), "got: {sql}");
        assert_eq!(params, &vec![FilterValue::Int(42)]);
    }

    #[tokio::test]
    async fn nested_op_disconnect_emits_update_set_null() {
        let engine = RecordingEngine::new();
        let op = NestedWriteOp::Disconnect {
            relation: "posts",
            target_table: "posts",
            foreign_key: "author_id",
            target_pk: "id",
            pk: FilterValue::Int(42),
        };
        op.execute(&engine, &FilterValue::Int(7)).await.unwrap();

        let stmts = engine.statements();
        assert_eq!(stmts.len(), 1);
        let (sql, params) = &stmts[0];
        assert!(sql.contains("UPDATE"), "got: {sql}");
        assert!(sql.contains("posts"), "got: {sql}");
        assert!(sql.contains("author_id"), "got: {sql}");
        assert!(sql.contains("NULL"), "got: {sql}");
        assert!(sql.contains("WHERE"), "got: {sql}");
        assert_eq!(params, &vec![FilterValue::Int(42)]);
    }

    #[tokio::test]
    async fn nested_op_update_plain_set() {
        use crate::inputs::WriteOp;
        let engine = RecordingEngine::new();
        let op = NestedWriteOp::Update {
            relation: "posts",
            target_table: "posts",
            target_pk: "id",
            pk: FilterValue::Int(42),
            payload: vec![(
                "title".to_string(),
                WriteOp::Set(FilterValue::String("renamed".to_string())),
            )],
        };
        op.execute(&engine, &FilterValue::Int(7)).await.unwrap();

        let stmts = engine.statements();
        assert_eq!(stmts.len(), 1);
        let (sql, params) = &stmts[0];
        assert!(sql.contains("UPDATE"), "got: {sql}");
        assert!(sql.contains("posts"), "got: {sql}");
        assert!(sql.contains("title"), "got: {sql}");
        assert!(sql.contains("SET"), "got: {sql}");
        assert!(sql.contains("WHERE"), "got: {sql}");
        assert!(sql.contains("$1"), "got: {sql}");
        assert!(sql.contains("$2"), "got: {sql}");
        assert_eq!(params.len(), 2);
        assert!(matches!(params[0], FilterValue::String(_)));
        assert_eq!(params[1], FilterValue::Int(42));
    }

    #[tokio::test]
    async fn nested_op_update_increment() {
        use crate::inputs::WriteOp;
        let engine = RecordingEngine::new();
        let op = NestedWriteOp::Update {
            relation: "posts",
            target_table: "posts",
            target_pk: "id",
            pk: FilterValue::Int(42),
            payload: vec![("views".to_string(), WriteOp::Increment(FilterValue::Int(1)))],
        };
        op.execute(&engine, &FilterValue::Int(7)).await.unwrap();

        let stmts = engine.statements();
        let (sql, _) = &stmts[0];
        // Postgres dialect quotes idents — fragment will read `"views" = "views" + $1`.
        assert!(sql.contains("+"), "got: {sql}");
        assert!(sql.contains("views"), "got: {sql}");
    }

    #[tokio::test]
    async fn nested_op_update_mixed_set_and_increment() {
        use crate::inputs::WriteOp;
        let engine = RecordingEngine::new();
        let op = NestedWriteOp::Update {
            relation: "posts",
            target_table: "posts",
            target_pk: "id",
            pk: FilterValue::Int(42),
            payload: vec![
                (
                    "title".to_string(),
                    WriteOp::Set(FilterValue::String("renamed".to_string())),
                ),
                ("views".to_string(), WriteOp::Increment(FilterValue::Int(1))),
            ],
        };
        op.execute(&engine, &FilterValue::Int(7)).await.unwrap();

        let stmts = engine.statements();
        let (sql, params) = &stmts[0];
        assert!(sql.contains("title"), "got: {sql}");
        assert!(sql.contains("views"), "got: {sql}");
        assert!(sql.contains("+"), "got: {sql}");
        // 2 SET params + 1 PK = 3 placeholders.
        assert!(sql.contains("$3"), "got: {sql}");
        assert_eq!(params.len(), 3);
    }

    #[tokio::test]
    async fn nested_op_update_empty_payload_is_noop() {
        let engine = RecordingEngine::new();
        let op = NestedWriteOp::Update {
            relation: "posts",
            target_table: "posts",
            target_pk: "id",
            pk: FilterValue::Int(42),
            payload: vec![],
        };
        op.execute(&engine, &FilterValue::Int(7)).await.unwrap();
        assert!(
            engine.statements().is_empty(),
            "empty payload should emit no SQL"
        );
    }

    #[tokio::test]
    async fn nested_op_update_many_with_filter() {
        use crate::inputs::WriteOp;
        let engine = RecordingEngine::new();
        let op = NestedWriteOp::UpdateMany {
            relation: "posts",
            target_table: "posts",
            foreign_key: "author_id",
            filter: Filter::Equals("published".into(), FilterValue::Bool(false)),
            payload: vec![("views".to_string(), WriteOp::Set(FilterValue::Int(0)))],
        };
        op.execute(&engine, &FilterValue::Int(7)).await.unwrap();

        let stmts = engine.statements();
        assert_eq!(stmts.len(), 1);
        let (sql, params) = &stmts[0];
        assert!(sql.contains("UPDATE"), "got: {sql}");
        assert!(sql.contains("posts"), "got: {sql}");
        assert!(sql.contains("author_id"), "got: {sql}");
        assert!(sql.contains("AND"), "got: {sql}");
        assert!(sql.contains("published"), "got: {sql}");
        // payload value + FK + filter value = 3 params
        assert_eq!(params.len(), 3);
        assert_eq!(params[0], FilterValue::Int(0));
        assert_eq!(params[1], FilterValue::Int(7));
        assert_eq!(params[2], FilterValue::Bool(false));
    }

    #[tokio::test]
    async fn nested_op_update_many_with_empty_filter() {
        use crate::inputs::WriteOp;
        let engine = RecordingEngine::new();
        let op = NestedWriteOp::UpdateMany {
            relation: "posts",
            target_table: "posts",
            foreign_key: "author_id",
            filter: Filter::None,
            payload: vec![("views".to_string(), WriteOp::Set(FilterValue::Int(0)))],
        };
        op.execute(&engine, &FilterValue::Int(7)).await.unwrap();

        let stmts = engine.statements();
        let (sql, params) = &stmts[0];
        assert!(sql.contains("UPDATE"), "got: {sql}");
        assert!(
            !sql.contains("AND"),
            "should omit AND when filter empty: {sql}"
        );
        // payload value + FK = 2 params
        assert_eq!(params.len(), 2);
    }

    #[test]
    fn test_nested_upsert_data() {
        let create: NestedCreateData<TestModel> =
            NestedCreateData::from_pairs([("title", FilterValue::String("New".to_string()))]);

        let upsert: NestedUpsertData<TestModel> = NestedUpsertData::new(
            Filter::Equals("id".into(), FilterValue::Int(1)),
            create,
            vec![(
                "title".to_string(),
                FilterValue::String("Updated".to_string()),
            )],
        );

        assert!(matches!(upsert.filter, Filter::Equals(..)));
        assert_eq!(upsert.create.data.len(), 1);
        assert_eq!(upsert.update.len(), 1);
    }

    #[tokio::test]
    async fn nested_op_upsert_single_statement_on_postgres() {
        use crate::inputs::WriteOp;
        // Postgres dialect supports `ON CONFLICT (...) DO UPDATE SET ...`,
        // so the executor must collapse the two-statement form into a
        // single `INSERT ... ON CONFLICT` statement.
        let engine = RecordingEngine::new();
        let op = NestedWriteOp::Upsert {
            relation: "posts",
            target_table: "posts",
            foreign_key: "author_id",
            target_pk: "id",
            pk: FilterValue::Int(99),
            create_payload: vec![("title".to_string(), FilterValue::String("new".to_string()))],
            update_payload: vec![("views".to_string(), WriteOp::Increment(FilterValue::Int(1)))],
        };
        op.execute(&engine, &FilterValue::Int(7)).await.unwrap();

        let stmts = engine.statements();
        assert_eq!(
            stmts.len(),
            1,
            "expected a single-statement upsert; got {stmts:#?}"
        );
        let (sql, params) = &stmts[0];
        assert!(sql.contains("INSERT INTO"), "got: {sql}");
        assert!(sql.contains("posts"), "got: {sql}");
        assert!(sql.contains("ON CONFLICT (\"id\")"), "got: {sql}");
        assert!(sql.contains("DO UPDATE SET"), "got: {sql}");
        // INSERT supplies $1 (title), $2 (author_id=parent_pk);
        // SET fragment uses $3 (views increment).
        assert!(
            sql.contains("VALUES ($1, $2)"),
            "INSERT VALUES placeholders: {sql}"
        );
        assert!(sql.contains("$3"), "got: {sql}");
        // Two insert values + one SET value.
        assert_eq!(params.len(), 3);
        assert_eq!(params[0], FilterValue::String("new".to_string()));
        assert_eq!(params[1], FilterValue::Int(7));
        assert_eq!(params[2], FilterValue::Int(1));
    }

    #[tokio::test]
    async fn nested_op_upsert_two_statement_fallback_on_mssql_update_path() {
        use crate::inputs::WriteOp;
        // MSSQL's `upsert_clause` returns empty → the executor must
        // fall back to the existing two-statement UPDATE-then-INSERT
        // form. Default affected-rows = 1 means UPDATE matches a row
        // and the INSERT phase must not run.
        let engine = RecordingEngine::mssql();
        let op = NestedWriteOp::Upsert {
            relation: "posts",
            target_table: "posts",
            foreign_key: "author_id",
            target_pk: "id",
            pk: FilterValue::Int(99),
            create_payload: vec![("title".to_string(), FilterValue::String("new".to_string()))],
            update_payload: vec![("views".to_string(), WriteOp::Increment(FilterValue::Int(1)))],
        };
        op.execute(&engine, &FilterValue::Int(7)).await.unwrap();

        let stmts = engine.statements();
        assert_eq!(
            stmts.len(),
            1,
            "expected only the UPDATE — INSERT should not have run"
        );
        let (sql, update_params) = &stmts[0];
        assert!(sql.starts_with("UPDATE"), "got: {sql}");
        assert!(!sql.contains("ON CONFLICT"), "got: {sql}");
        assert!(!sql.contains("ON DUPLICATE"), "got: {sql}");
        // MSSQL uses bracket-quoted identifiers and @P-prefixed placeholders.
        assert!(sql.contains("[posts]"), "got: {sql}");
        assert!(sql.contains("@P1"), "SET clause should use @P1: {sql}");
        assert!(sql.contains("@P2"), "WHERE clause should use @P2: {sql}");
        // Two params: the increment value ($1) and the pk ($2).
        assert_eq!(update_params.len(), 2);
        assert_eq!(update_params[0], FilterValue::Int(1)); // increment value
        assert_eq!(update_params[1], FilterValue::Int(99)); // pk
    }

    #[tokio::test]
    async fn nested_op_upsert_two_statement_fallback_on_mssql_insert_path() {
        use crate::inputs::WriteOp;
        // First execute_raw (UPDATE) returns 0; the executor must
        // proceed to emit a separate INSERT.
        let engine = RecordingEngine::mssql_with_affected(vec![0, 1]);
        let op = NestedWriteOp::Upsert {
            relation: "posts",
            target_table: "posts",
            foreign_key: "author_id",
            target_pk: "id",
            pk: FilterValue::Int(99),
            create_payload: vec![("title".to_string(), FilterValue::String("new".to_string()))],
            update_payload: vec![("views".to_string(), WriteOp::Increment(FilterValue::Int(1)))],
        };
        op.execute(&engine, &FilterValue::Int(7)).await.unwrap();

        let stmts = engine.statements();
        assert_eq!(stmts.len(), 2, "expected UPDATE then INSERT");
        let (update_sql, _) = &stmts[0];
        assert!(update_sql.starts_with("UPDATE"), "got: {update_sql}");
        let (insert_sql, insert_params) = &stmts[1];
        assert!(insert_sql.starts_with("INSERT INTO"), "got: {insert_sql}");
        assert!(!insert_sql.contains("ON CONFLICT"), "got: {insert_sql}");
        assert!(insert_sql.contains("[posts]"), "got: {insert_sql}");
        assert!(insert_sql.contains("[author_id]"), "got: {insert_sql}");
        assert_eq!(insert_params.len(), 2);
        assert_eq!(insert_params[0], FilterValue::String("new".to_string()));
        assert_eq!(insert_params[1], FilterValue::Int(7));
    }

    #[tokio::test]
    async fn nested_op_connect_or_create_connect_path_when_affected() {
        // Default RecordingEngine returns 1 from execute_raw, so the
        // UPDATE matches at least one row and the INSERT phase must not
        // run.
        let engine = RecordingEngine::with_affected(vec![1]);
        let op = NestedWriteOp::ConnectOrCreate {
            relation: "posts",
            target_table: "posts",
            foreign_key: "author_id",
            where_filter: Filter::Equals("id".into(), FilterValue::Int(42)),
            create_payload: vec![(
                "title".to_string(),
                FilterValue::String("fallback".to_string()),
            )],
        };
        op.execute(&engine, &FilterValue::Int(7)).await.unwrap();

        let stmts = engine.statements();
        assert_eq!(
            stmts.len(),
            1,
            "expected only the UPDATE — INSERT should not have run"
        );
        let (sql, params) = &stmts[0];
        assert!(sql.contains("UPDATE"), "got: {sql}");
        assert!(!sql.contains("INSERT"), "got: {sql}");
        assert!(sql.contains("posts"), "got: {sql}");
        assert!(sql.contains("author_id"), "got: {sql}");
        // params: parent_pk ($1) + filter value ($2)
        assert_eq!(params.len(), 2);
        assert_eq!(params[0], FilterValue::Int(7));
        assert_eq!(params[1], FilterValue::Int(42));
    }

    #[tokio::test]
    async fn nested_op_connect_or_create_create_path_when_zero_affected() {
        // UPDATE returns 0 (no matching row) → executor must emit the
        // INSERT with the FK spliced in. Second call (the INSERT)
        // returns 1.
        let engine = RecordingEngine::with_affected(vec![0, 1]);
        let op = NestedWriteOp::ConnectOrCreate {
            relation: "posts",
            target_table: "posts",
            foreign_key: "author_id",
            where_filter: Filter::Equals("id".into(), FilterValue::Int(42)),
            create_payload: vec![(
                "title".to_string(),
                FilterValue::String("fallback".to_string()),
            )],
        };
        op.execute(&engine, &FilterValue::Int(7)).await.unwrap();

        let stmts = engine.statements();
        assert_eq!(stmts.len(), 2);
        let (update_sql, _) = &stmts[0];
        assert!(update_sql.contains("UPDATE"), "got: {update_sql}");
        let (insert_sql, insert_params) = &stmts[1];
        assert!(insert_sql.contains("INSERT INTO"), "got: {insert_sql}");
        assert!(insert_sql.contains("posts"), "got: {insert_sql}");
        assert!(insert_sql.contains("title"), "got: {insert_sql}");
        assert!(insert_sql.contains("author_id"), "got: {insert_sql}");
        // create payload value + FK (parent_pk) = 2 params; parent_pk
        // must be last so the FK column lines up with $2.
        assert_eq!(insert_params.len(), 2);
        assert_eq!(
            insert_params[0],
            FilterValue::String("fallback".to_string())
        );
        assert_eq!(insert_params[1], FilterValue::Int(7));
    }

    #[tokio::test]
    async fn nested_op_set_with_empty_list_clears_all_children() {
        // Empty set_pks → one UPDATE with `WHERE fk = $1`, no NOT IN clause,
        // no connect step.
        let engine = RecordingEngine::new();
        let op = NestedWriteOp::Set {
            relation: "posts",
            target_table: "posts",
            foreign_key: "author_id",
            target_pk: "id",
            set_pks: vec![],
        };
        op.execute(&engine, &FilterValue::Int(7)).await.unwrap();

        let stmts = engine.statements();
        assert_eq!(stmts.len(), 1, "expected only the disconnect-all UPDATE");
        let (sql, params) = &stmts[0];
        assert!(sql.contains("UPDATE"), "got: {sql}");
        assert!(sql.contains("posts"), "got: {sql}");
        assert!(sql.contains("author_id"), "got: {sql}");
        assert!(sql.contains("= NULL"), "got: {sql}");
        assert!(!sql.contains("NOT IN"), "got: {sql}");
        assert!(!sql.contains(" IN ("), "got: {sql}");
        // Only the parent_pk param.
        assert_eq!(params.len(), 1);
        assert_eq!(params[0], FilterValue::Int(7));
    }

    #[tokio::test]
    async fn nested_op_set_with_non_empty_list_emits_disconnect_then_connect() {
        let engine = RecordingEngine::new();
        let op = NestedWriteOp::Set {
            relation: "posts",
            target_table: "posts",
            foreign_key: "author_id",
            target_pk: "id",
            set_pks: vec![
                FilterValue::Int(1),
                FilterValue::Int(2),
                FilterValue::Int(3),
            ],
        };
        op.execute(&engine, &FilterValue::Int(7)).await.unwrap();

        let stmts = engine.statements();
        assert_eq!(stmts.len(), 2);
        let (disconnect_sql, disconnect_params) = &stmts[0];
        assert!(disconnect_sql.contains("UPDATE"), "got: {disconnect_sql}");
        assert!(disconnect_sql.contains("posts"), "got: {disconnect_sql}");
        assert!(
            disconnect_sql.contains("author_id"),
            "got: {disconnect_sql}"
        );
        assert!(disconnect_sql.contains("= NULL"), "got: {disconnect_sql}");
        assert!(disconnect_sql.contains("NOT IN"), "got: {disconnect_sql}");
        // params: parent_pk ($1) + 3 set pks ($2..$4)
        assert_eq!(disconnect_params.len(), 4);
        assert_eq!(disconnect_params[0], FilterValue::Int(7));
        assert_eq!(disconnect_params[1], FilterValue::Int(1));
        assert_eq!(disconnect_params[2], FilterValue::Int(2));
        assert_eq!(disconnect_params[3], FilterValue::Int(3));

        let (connect_sql, connect_params) = &stmts[1];
        assert!(connect_sql.contains("UPDATE"), "got: {connect_sql}");
        assert!(connect_sql.contains("posts"), "got: {connect_sql}");
        assert!(connect_sql.contains("author_id"), "got: {connect_sql}");
        assert!(connect_sql.contains(" IN ("), "got: {connect_sql}");
        assert!(!connect_sql.contains("NOT IN"), "got: {connect_sql}");
        // params: parent_pk ($1) + 3 set pks ($2..$4)
        assert_eq!(connect_params.len(), 4);
        assert_eq!(connect_params[0], FilterValue::Int(7));
        assert_eq!(connect_params[1], FilterValue::Int(1));
        assert_eq!(connect_params[2], FilterValue::Int(2));
        assert_eq!(connect_params[3], FilterValue::Int(3));
    }

    #[tokio::test]
    async fn nested_op_set_with_single_element_uses_single_placeholder_in_lists() {
        let engine = RecordingEngine::new();
        let op = NestedWriteOp::Set {
            relation: "posts",
            target_table: "posts",
            foreign_key: "author_id",
            target_pk: "id",
            set_pks: vec![FilterValue::Int(5)],
        };
        op.execute(&engine, &FilterValue::Int(7)).await.unwrap();

        let stmts = engine.statements();
        assert_eq!(stmts.len(), 2);
        let (disconnect_sql, _) = &stmts[0];
        // The NOT IN list has one placeholder.
        assert!(
            disconnect_sql.contains("NOT IN ($2)"),
            "got: {disconnect_sql}"
        );
        let (connect_sql, _) = &stmts[1];
        assert!(connect_sql.contains(" IN ($2)"), "got: {connect_sql}");
        assert!(!connect_sql.contains("NOT IN"), "got: {connect_sql}");
    }

    #[tokio::test]
    async fn nested_op_set_disconnect_clears_only_current_parents_children() {
        // The disconnect UPDATE must be scoped to `WHERE fk = $parent AND ...`
        // — without this clause, we'd clear children belonging to other parents.
        let engine = RecordingEngine::new();
        let op = NestedWriteOp::Set {
            relation: "posts",
            target_table: "posts",
            foreign_key: "author_id",
            target_pk: "id",
            set_pks: vec![FilterValue::Int(1)],
        };
        op.execute(&engine, &FilterValue::Int(7)).await.unwrap();

        let stmts = engine.statements();
        let (disconnect_sql, _) = &stmts[0];
        // The disconnect must scope to the parent's children.
        assert!(
            disconnect_sql.contains("author_id\" = $1"),
            "expected `author_id = $1` clause; got: {disconnect_sql}"
        );
    }

    #[tokio::test]
    async fn nested_op_connect_or_create_rejects_empty_where() {
        // Filter::None would lower to `WHERE TRUE` and rewrite every row.
        // The executor must reject this defensively before issuing SQL.
        let engine = RecordingEngine::new();
        let op = NestedWriteOp::ConnectOrCreate {
            relation: "posts",
            target_table: "posts",
            foreign_key: "author_id",
            where_filter: Filter::None,
            create_payload: vec![(
                "title".to_string(),
                FilterValue::String("fallback".to_string()),
            )],
        };
        let err = op
            .execute(&engine, &FilterValue::Int(7))
            .await
            .expect_err("empty where must be rejected");
        let op_ctx = err.context.operation.clone().unwrap_or_default();
        assert!(op_ctx.contains("ConnectOrCreate"), "got: {op_ctx}");
        // No SQL should have been emitted.
        assert!(engine.statements().is_empty());
    }

    #[tokio::test]
    async fn nested_op_upsert_single_statement_empty_update_payload_emits_do_nothing() {
        // PG dialect → single-statement path. Empty update_payload should emit
        // INSERT INTO ... VALUES (...) ON CONFLICT (target_pk) DO NOTHING
        // (per the upsert_do_nothing_clause helper added in 8f01cab).
        let engine = RecordingEngine::new();
        let op = NestedWriteOp::Upsert {
            relation: "posts",
            target_table: "posts",
            foreign_key: "author_id",
            target_pk: "id",
            pk: FilterValue::Int(99),
            create_payload: vec![("title".to_string(), FilterValue::String("new".into()))],
            update_payload: vec![],
        };
        op.execute(&engine, &FilterValue::Int(7)).await.unwrap();

        let stmts = engine.statements();
        assert_eq!(
            stmts.len(),
            1,
            "expected one INSERT ... DO NOTHING; got {stmts:#?}"
        );
        let (sql, params) = &stmts[0];
        assert!(sql.starts_with("INSERT INTO"), "got: {sql}");
        assert!(sql.contains("posts"), "got: {sql}");
        assert!(sql.contains("ON CONFLICT (\"id\")"), "got: {sql}");
        assert!(sql.contains("DO NOTHING"), "got: {sql}");
        // Two insert values (title + FK); no SET params.
        assert_eq!(params.len(), 2);
        assert_eq!(params[0], FilterValue::String("new".into()));
        assert_eq!(params[1], FilterValue::Int(7));
    }

    #[tokio::test]
    async fn nested_op_upsert_two_statement_fallback_empty_update_payload_emits_bare_insert() {
        // MSSQL dialect → two-statement fallback. On the fallback path,
        // empty update_payload skips the UPDATE entirely and emits a bare INSERT
        // (if the row already exists the engine surfaces a PK unique violation,
        // which is correct insert-or-fail semantics on dialects without native
        // upsert syntax). See production code comment at the
        // `if update_payload.is_empty()` guard in the two-statement fallback path.
        let engine = RecordingEngine::mssql();
        let op = NestedWriteOp::Upsert {
            relation: "posts",
            target_table: "posts",
            foreign_key: "author_id",
            target_pk: "id",
            pk: FilterValue::Int(99),
            create_payload: vec![("title".to_string(), FilterValue::String("new".into()))],
            update_payload: vec![],
        };
        op.execute(&engine, &FilterValue::Int(7)).await.unwrap();

        let stmts = engine.statements();
        assert_eq!(stmts.len(), 1, "expected one bare INSERT; got {stmts:#?}");
        let (sql, params) = &stmts[0];
        assert!(sql.starts_with("INSERT INTO"), "got: {sql}");
        assert!(sql.contains("[posts]"), "got: {sql}");
        assert!(!sql.contains("ON CONFLICT"), "got: {sql}");
        assert_eq!(params.len(), 2);
        assert_eq!(params[0], FilterValue::String("new".into()));
        assert_eq!(params[1], FilterValue::Int(7));
    }

    #[tokio::test]
    async fn nested_op_upsert_single_statement_all_unset_update_payload() {
        use crate::inputs::WriteOp;
        // Unset emits `col = NULL` literal (no placeholder consumed).
        // The placeholder accounting must remain consistent: only INSERT
        // values consume placeholders.
        let engine = RecordingEngine::new();
        let op = NestedWriteOp::Upsert {
            relation: "posts",
            target_table: "posts",
            foreign_key: "author_id",
            target_pk: "id",
            pk: FilterValue::Int(99),
            create_payload: vec![("title".to_string(), FilterValue::String("new".into()))],
            update_payload: vec![("deleted_at".to_string(), WriteOp::Unset)],
        };
        op.execute(&engine, &FilterValue::Int(7)).await.unwrap();

        let stmts = engine.statements();
        assert_eq!(
            stmts.len(),
            1,
            "expected one INSERT...ON CONFLICT statement; got {stmts:#?}"
        );
        let (sql, params) = &stmts[0];
        assert!(sql.starts_with("INSERT INTO"), "got: {sql}");
        assert!(
            sql.contains("ON CONFLICT (\"id\") DO UPDATE SET"),
            "got: {sql}"
        );
        assert!(sql.contains("\"deleted_at\" = NULL"), "got: {sql}");
        // Only INSERT params: title + FK. No SET param (Unset consumes none).
        assert_eq!(params.len(), 2);
        assert_eq!(params[0], FilterValue::String("new".into()));
        assert_eq!(params[1], FilterValue::Int(7));
    }

    #[tokio::test]
    async fn nested_op_upsert_empty_create_payload_returns_invalid_input() {
        use crate::inputs::WriteOp;
        let engine = RecordingEngine::new();
        let op = NestedWriteOp::Upsert {
            relation: "posts",
            target_table: "posts",
            foreign_key: "author_id",
            target_pk: "id",
            pk: FilterValue::Int(99),
            create_payload: vec![],
            update_payload: vec![("views".to_string(), WriteOp::Increment(FilterValue::Int(1)))],
        };
        let err = op.execute(&engine, &FilterValue::Int(7)).await.unwrap_err();
        assert_eq!(
            err.code,
            crate::error::ErrorCode::InvalidParameter,
            "expected InvalidParameter (invalid_input), got: {err:?}"
        );
        let msg = format!("{err}");
        assert!(
            msg.contains("create_payload") || msg.contains("create column"),
            "msg: {msg}"
        );
    }

    #[tokio::test]
    async fn nested_op_upsert_on_notsql_returns_unsupported_not_panic() {
        use crate::inputs::WriteOp;
        let engine = RecordingEngine::notsql();
        let op = NestedWriteOp::Upsert {
            relation: "posts",
            target_table: "posts",
            foreign_key: "author_id",
            target_pk: "id",
            pk: FilterValue::Int(99),
            create_payload: vec![("title".to_string(), FilterValue::String("x".into()))],
            update_payload: vec![("views".to_string(), WriteOp::Increment(FilterValue::Int(1)))],
        };
        let err = op.execute(&engine, &FilterValue::Int(7)).await.unwrap_err();
        let msg = format!("{err}");
        assert!(
            msg.contains("Upsert is not supported")
                || msg.contains("unsupported")
                || msg.contains("Unsupported"),
            "msg: {msg}"
        );
        assert_eq!(
            engine.statements().len(),
            0,
            "no SQL should have been emitted"
        );
    }
}