fraiseql_db/postgres/adapter/

database.rs

//! `DatabaseAdapter` and `SupportsMutations` implementations for `PostgresAdapter`.

use std::sync::Arc;

use async_trait::async_trait;
use bytes::BufMut as _;
use fraiseql_error::{FraiseQLError, Result};
use tokio_postgres::Row;

use super::{
    PostgresAdapter, build_projection_select_sql, build_where_select_sql,
    build_where_select_sql_ordered,
};
use crate::{
    identifier::quote_postgres_identifier,
    traits::{DatabaseAdapter, ProjectionRequest, SupportsMutations},
    types::{
        DatabaseType, JsonbValue, PoolMetrics, QueryParam,
        sql_hints::{OrderByClause, SqlProjectionHint},
    },
    where_clause::WhereClause,
};

/// PostgreSQL SQLSTATE 42703: undefined column.
const PG_UNDEFINED_COLUMN: &str = "42703";

/// A flexible SQL parameter that binds to any PostgreSQL type.
///
/// Solves the impedance mismatch between `serde_json::Value` (only accepts JSON/JSONB)
/// and `Option<String>` (only accepts text-family types) when binding function-call
/// arguments whose types are resolved at runtime from the function signature.
///
/// Serialisation strategy (binary wire format):
/// - `JSONB`: 1-byte version header (1) + UTF-8 JSON bytes
/// - `JSON`: UTF-8 JSON bytes
/// - `UUID`: 16-byte big-endian UUID
/// - `INT4`: 4-byte big-endian i32
/// - `INT8`: 8-byte big-endian i64
/// - `BOOL`: 1-byte (0 or 1)
/// - All other types: UTF-8 bytes (PostgreSQL text binary = raw UTF-8)
#[derive(Debug)]
enum FlexParam {
    /// SQL NULL — accepted by any PostgreSQL type.
    Null,
    /// A text-encoded value; binary-serialised according to the server-resolved type.
    Text(String),
}

impl tokio_postgres::types::ToSql for FlexParam {
    fn to_sql(
        &self,
        ty: &tokio_postgres::types::Type,
        out: &mut bytes::BytesMut,
    ) -> std::result::Result<tokio_postgres::types::IsNull, Box<dyn std::error::Error + Sync + Send>>
    {
        use tokio_postgres::types::{IsNull, Type};
        match self {
            Self::Null => Ok(IsNull::Yes),
            Self::Text(s) => {
                if *ty == Type::JSONB {
                    // JSONB binary wire format: 1-byte version (1) + JSON bytes
                    out.put_u8(1);
                    out.extend_from_slice(s.as_bytes());
                } else if *ty == Type::JSON {
                    out.extend_from_slice(s.as_bytes());
                } else if *ty == Type::UUID {
                    let uuid = uuid::Uuid::parse_str(s)?;
                    out.extend_from_slice(uuid.as_bytes());
                } else if *ty == Type::INT4 {
                    let n: i32 = s.parse()?;
                    out.put_i32(n);
                } else if *ty == Type::INT8 {
                    let n: i64 = s.parse()?;
                    out.put_i64(n);
                } else if *ty == Type::BOOL {
                    let b: bool = s.parse()?;
                    out.put_u8(u8::from(b));
                } else {
                    // TEXT, VARCHAR, BPCHAR, NAME, UNKNOWN, and any user-defined type:
                    // UTF-8 bytes are the binary wire representation for text-family types.
                    out.extend_from_slice(s.as_bytes());
                }
                Ok(IsNull::No)
            },
        }
    }

    fn accepts(_ty: &tokio_postgres::types::Type) -> bool {
        // Accepts all types; per-type serialisation is handled in `to_sql`.
        true
    }

    fn to_sql_checked(
        &self,
        ty: &tokio_postgres::types::Type,
        out: &mut bytes::BytesMut,
    ) -> std::result::Result<tokio_postgres::types::IsNull, Box<dyn std::error::Error + Sync + Send>>
    {
        // `accepts()` returns true for all types, so the standard WrongType check is
        // unnecessary.  Delegate directly to `to_sql`.
        self.to_sql(ty, out)
    }
}

/// Enrich a `FraiseQLError::Database` error for PostgreSQL SQLSTATE 42703 (undefined column)
/// when the WHERE clause contains `NativeField` conditions.
///
/// Native columns may be inferred automatically at compile time from `ID`/`UUID`-typed
/// arguments.  If the column does not exist on the target table at runtime, the raw
/// PostgreSQL error is replaced with a diagnostic message that names the native columns
/// involved and explains how to fix the schema.
fn enrich_undefined_column_error(
    err: FraiseQLError,
    view: &str,
    where_clause: Option<&WhereClause>,
) -> FraiseQLError {
    let FraiseQLError::Database { ref sql_state, .. } = err else {
        return err;
    };
    if sql_state.as_deref() != Some(PG_UNDEFINED_COLUMN) {
        return err;
    }
    let native_cols: Vec<&str> =
        where_clause.map(|wc| wc.native_column_names()).unwrap_or_default();
    if native_cols.is_empty() {
        return err;
    }
    FraiseQLError::Database {
        message:   format!(
            "Column(s) {:?} referenced as native column(s) on `{view}` do not exist. \
             These columns were auto-inferred from ID/UUID-typed query arguments. \
             Either add the column(s) to the table/view, or set \
             `native_columns = {{}}` explicitly in your schema to disable inference.",
            native_cols,
        ),
        sql_state: Some(PG_UNDEFINED_COLUMN.to_string()),
    }
}

/// Convert a single `tokio_postgres::Row` into a `HashMap<String, serde_json::Value>`.
///
/// Tries each PostgreSQL type in priority order; falls back to `Null` for
/// types that cannot be represented as JSON.
fn row_to_map(row: &Row) -> std::collections::HashMap<String, serde_json::Value> {
    let mut map = std::collections::HashMap::new();
    for (idx, column) in row.columns().iter().enumerate() {
        let column_name = column.name().to_string();
        let value: serde_json::Value = if let Ok(v) = row.try_get::<_, i32>(idx) {
            serde_json::json!(v)
        } else if let Ok(v) = row.try_get::<_, i64>(idx) {
            serde_json::json!(v)
        } else if let Ok(v) = row.try_get::<_, f64>(idx) {
            serde_json::json!(v)
        } else if let Ok(v) = row.try_get::<_, String>(idx) {
            serde_json::json!(v)
        } else if let Ok(v) = row.try_get::<_, bool>(idx) {
            serde_json::json!(v)
        } else if let Ok(v) = row.try_get::<_, Vec<String>>(idx) {
            // TEXT[] columns (e.g. `app.mutation_response.updated_fields`) — without
            // this branch a non-null text array falls through to Null and a parser
            // expecting a sequence fails. Must precede the jsonb branch (a jsonb
            // column never deserializes as Vec<String>, so ordering is safe).
            serde_json::json!(v)
        } else if let Ok(v) = row.try_get::<_, serde_json::Value>(idx) {
            v
        } else {
            serde_json::Value::Null
        };
        map.insert(column_name, value);
    }
    map
}

/// Apply transaction-local session variables on an in-progress transaction.
///
/// Each `(name, value)` pair is set with `SELECT set_config($1, $2, true)`, so
/// the values are scoped to `txn` and visible to every statement run on it
/// (fixes #329). The caller is responsible for committing or rolling back.
pub(super) async fn apply_session_vars(
    txn: &tokio_postgres::Transaction<'_>,
    session_vars: &[(&str, &str)],
) -> Result<()> {
    for (name, value) in session_vars {
        // A var carrying the clock-timestamp directive (e.g. fraiseql.started_at)
        // is stamped with the DB clock at apply time, on this very transaction, so
        // the start timestamp and the close-of-interval at the outbox write share
        // one clock (no app↔DB skew). All other vars bind their literal value.
        if *value == crate::changelog::CLOCK_TIMESTAMP_DIRECTIVE {
            txn.execute("SELECT set_config($1, clock_timestamp()::text, true)", &[name])
                .await
                .map_err(|e| FraiseQLError::Database {
                    message:   format!("set_config({name:?}, clock_timestamp()) failed: {e}"),
                    sql_state: e.code().map(|c| c.code().to_string()),
                })?;
        } else {
            txn.execute("SELECT set_config($1, $2, true)", &[name, value])
                .await
                .map_err(|e| FraiseQLError::Database {
                    message:   format!("set_config({name:?}) failed: {e}"),
                    sql_state: e.code().map(|c| c.code().to_string()),
                })?;
        }
    }
    Ok(())
}

/// Build the single statement that runs a mutation function and writes its
/// `core.tb_entity_change_log` outbox row in the same transaction (the Change
/// Spine transactional outbox).
///
/// The function call is materialised once (`WITH r AS MATERIALIZED`, so a
/// volatile mutation function executes **exactly once** even though two CTEs
/// read it), a data-modifying CTE INSERTs the change-log row for an effective
/// change (`succeeded AND state_changed`), and the primary `SELECT * FROM r`
/// returns the function's row unchanged to the caller. The changed-entity
/// columns (`object_id`, `object_data`, `updated_fields`, `cascade`) come from
/// the function's own `app.mutation_response` row; `$<n+1>` is the NOT-NULL
/// `object_type` fallback, `$<n+2>` is the `modification_type` verb,
/// `$<n+3>` is the envelope `tenant_id` (the Trinity public-facing UUID, NULL
/// for system / unauthenticated / non-UUID-tenant rows), `$<n+4>` is the
/// `trace_id` (the request's W3C trace id, plain text), `$<n+5>` is the
/// `schema_version` (the compiled schema's content hash, plain text), and
/// `$<n+6>` is the `trace_context` (the full W3C trace context, cast `::jsonb`),
/// where `n` = `n_args` (the number of function arguments). The envelope params are
/// appended **after** the function args so the SQL text stays deterministic per
/// `(function, n_args)` — `prepare_cached` keys the statement by text, so the
/// column list and placeholder positions must never depend on the param *values*.
///
/// `started_at`/`duration_ms` read `fraiseql.started_at` (set txn-locally by the
/// caller) on the DB clock — the canonical computation from
/// [`crate::changelog::duration_ms_sql`], stamped with
/// [`crate::changelog::DURATION_CALC_VERSION`]. `commit_time` is the DB clock at
/// INSERT; `seq` is omitted so the column's `SEQUENCE` default fires (so any
/// INSERTer, incl. cooperative external producers, gets a monotonic value).
pub(super) fn build_changelog_cte_sql(quoted_fn: &str, n_args: usize) -> String {
    let placeholders: Vec<String> = (1..=n_args).map(|i| format!("${i}")).collect();
    let object_type_idx = n_args + 1;
    let modification_type_idx = n_args + 2;
    let tenant_id_idx = n_args + 3;
    let trace_id_idx = n_args + 4;
    let schema_version_idx = n_args + 5;
    let trace_context_idx = n_args + 6;
    let started_var = crate::changelog::STARTED_AT_VAR;
    let duration = crate::changelog::duration_ms_sql(started_var);
    let calc_version = crate::changelog::DURATION_CALC_VERSION;
    format!(
        "WITH r AS MATERIALIZED (SELECT * FROM {quoted_fn}({args})), \
         _changelog AS ( \
           INSERT INTO core.tb_entity_change_log \
             (object_type, modification_type, object_id, object_data, \
              updated_fields, cascade, started_at, duration_ms, extra_metadata, \
              tenant_id, trace_id, schema_version, trace_context, commit_time) \
           SELECT \
             COALESCE(r.entity_type, ${object_type_idx}), \
             ${modification_type_idx}, \
             r.entity_id, r.entity, r.updated_fields, r.cascade, \
             current_setting('{started_var}')::timestamptz, \
             {duration}, \
             jsonb_build_object('duration_calc_version', {calc_version}::int), \
             ${tenant_id_idx}::uuid, \
             ${trace_id_idx}, \
             ${schema_version_idx}, \
             ${trace_context_idx}::jsonb, \
             clock_timestamp() \
           FROM r \
           WHERE r.succeeded AND r.state_changed \
           RETURNING 1 \
         ) \
         SELECT * FROM r",
        args = placeholders.join(", "),
    )
}

/// Prepare `sql` on `client` using deadpool's **per-connection statement cache**.
///
/// The mutation function-call path sends the same statement (a fixed
/// `SELECT * FROM fn(...)` or the change-log CTE) on every call, so without
/// caching PostgreSQL re-parses and re-plans it for each mutation — the dominant
/// hot-path cost (the complex outbox CTE in particular). `prepare_cached` keys
/// the parsed/planned [`tokio_postgres::Statement`] by SQL text per connection
/// and reuses it across calls, so the parse/plan happens once per connection.
///
/// Returns an owned `Statement` (releasing the `&client` borrow), so it can be
/// prepared before `client.build_transaction()` and used inside that transaction.
async fn prepare_cached_stmt(
    client: &deadpool_postgres::Client,
    sql: &str,
) -> Result<tokio_postgres::Statement> {
    client.prepare_cached(sql).await.map_err(|e| FraiseQLError::Database {
        message:   format!("Failed to prepare statement: {e}"),
        sql_state: e.code().map(|c| c.code().to_string()),
    })
}

// Reason: DatabaseAdapter is defined with #[async_trait]; all implementations must match
// its transformed method signatures to satisfy the trait contract
// async_trait: dyn-dispatch required; remove when RTN + Send is stable (RFC 3425)
#[async_trait]
impl DatabaseAdapter for PostgresAdapter {
    async fn execute_with_projection(
        &self,
        view: &str,
        projection: Option<&SqlProjectionHint>,
        where_clause: Option<&WhereClause>,
        limit: Option<u32>,
        offset: Option<u32>,
        order_by: Option<&[OrderByClause]>,
    ) -> Result<Vec<JsonbValue>> {
        self.execute_with_projection_impl(view, projection, where_clause, limit, offset, order_by)
            .await
    }

    async fn execute_where_query(
        &self,
        view: &str,
        where_clause: Option<&WhereClause>,
        limit: Option<u32>,
        offset: Option<u32>,
        order_by: Option<&[OrderByClause]>,
    ) -> Result<Vec<JsonbValue>> {
        let (sql, typed_params) =
            build_where_select_sql_ordered(view, where_clause, limit, offset, order_by)?;

        let param_refs = crate::types::as_sql_param_refs(&typed_params);

        self.execute_raw(&sql, &param_refs)
            .await
            .map_err(|e| enrich_undefined_column_error(e, view, where_clause))
    }

    async fn explain_where_query(
        &self,
        view: &str,
        where_clause: Option<&WhereClause>,
        limit: Option<u32>,
        offset: Option<u32>,
    ) -> Result<serde_json::Value> {
        let (select_sql, typed_params) = build_where_select_sql(view, where_clause, limit, offset)?;
        // Defense-in-depth: compiler-generated SQL should never contain a
        // semicolon, but guard against it to prevent statement injection.
        if select_sql.contains(';') {
            return Err(FraiseQLError::Validation {
                message: "EXPLAIN SQL must be a single statement".into(),
                path:    None,
            });
        }
        let explain_sql = format!("EXPLAIN (ANALYZE, BUFFERS, FORMAT JSON) {select_sql}");

        let param_refs = crate::types::as_sql_param_refs(&typed_params);

        let client = self.acquire_connection_with_retry().await?;
        let rows = client.query(explain_sql.as_str(), &param_refs).await.map_err(|e| {
            FraiseQLError::Database {
                message:   format!("EXPLAIN ANALYZE failed: {e}"),
                sql_state: e.code().map(|c| c.code().to_string()),
            }
        })?;

        if let Some(row) = rows.first() {
            let plan: serde_json::Value = row.try_get(0).map_err(|e| FraiseQLError::Database {
                message:   format!("Failed to parse EXPLAIN output: {e}"),
                sql_state: None,
            })?;
            Ok(plan)
        } else {
            Ok(serde_json::Value::Null)
        }
    }

    fn database_type(&self) -> DatabaseType {
        DatabaseType::PostgreSQL
    }

    async fn health_check(&self) -> Result<()> {
        // Use retry logic for health check to avoid false negatives during pool exhaustion
        let client = self.acquire_connection_with_retry().await?;

        client.query("SELECT 1", &[]).await.map_err(|e| FraiseQLError::Database {
            message:   format!("Health check failed: {e}"),
            sql_state: e.code().map(|c| c.code().to_string()),
        })?;

        Ok(())
    }

    #[allow(clippy::cast_possible_truncation)] // Reason: value is bounded; truncation cannot occur in practice
    fn pool_metrics(&self) -> PoolMetrics {
        let status = self.pool.status();

        PoolMetrics {
            total_connections:  status.size as u32,
            idle_connections:   status.available as u32,
            active_connections: (status.size - status.available) as u32,
            waiting_requests:   status.waiting as u32,
        }
    }

    /// # Security
    ///
    /// `sql` **must** be compiler-generated. Never pass user-supplied strings
    /// directly — doing so would open SQL-injection vulnerabilities.
    async fn execute_raw_query(
        &self,
        sql: &str,
    ) -> Result<Vec<std::collections::HashMap<String, serde_json::Value>>> {
        // Use retry logic for connection acquisition
        let client = self.acquire_connection_with_retry().await?;

        let rows: Vec<Row> = client.query(sql, &[]).await.map_err(|e| FraiseQLError::Database {
            message:   format!("Query execution failed: {e}"),
            sql_state: e.code().map(|c| c.code().to_string()),
        })?;

        // Convert each row to HashMap<String, Value>
        let results: Vec<std::collections::HashMap<String, serde_json::Value>> =
            rows.iter().map(row_to_map).collect();

        Ok(results)
    }

    async fn execute_parameterized_aggregate(
        &self,
        sql: &str,
        params: &[serde_json::Value],
    ) -> Result<Vec<std::collections::HashMap<String, serde_json::Value>>> {
        // Convert serde_json::Value params to QueryParam so that strings are bound
        // as TEXT (not JSONB), which is required for correct WHERE comparisons against
        // data->>'field' expressions that return TEXT.
        let typed: Vec<QueryParam> = params.iter().cloned().map(QueryParam::from).collect();
        let param_refs = crate::types::as_sql_param_refs(&typed);

        let client = self.acquire_connection_with_retry().await?;
        let rows: Vec<Row> =
            client.query(sql, &param_refs).await.map_err(|e| FraiseQLError::Database {
                message:   format!("Parameterized aggregate query failed: {e}"),
                sql_state: e.code().map(|c| c.code().to_string()),
            })?;

        let results: Vec<std::collections::HashMap<String, serde_json::Value>> =
            rows.iter().map(row_to_map).collect();

        Ok(results)
    }

    async fn execute_parameterized_aggregate_with_session(
        &self,
        sql: &str,
        params: &[serde_json::Value],
        session_vars: &[(&str, &str)],
    ) -> Result<Vec<std::collections::HashMap<String, serde_json::Value>>> {
        if session_vars.is_empty() {
            return self.execute_parameterized_aggregate(sql, params).await;
        }

        let typed: Vec<QueryParam> = params.iter().cloned().map(QueryParam::from).collect();
        let param_refs = crate::types::as_sql_param_refs(&typed);

        let mut client = self.acquire_connection_with_retry().await?;
        let txn =
            client.build_transaction().start().await.map_err(|e| FraiseQLError::Database {
                message:   format!("Failed to start session-var transaction: {e}"),
                sql_state: e.code().map(|c| c.code().to_string()),
            })?;
        apply_session_vars(&txn, session_vars).await?;
        let rows: Vec<Row> =
            txn.query(sql, &param_refs).await.map_err(|e| FraiseQLError::Database {
                message:   format!("Parameterized aggregate query failed: {e}"),
                sql_state: e.code().map(|c| c.code().to_string()),
            })?;
        txn.commit().await.map_err(|e| FraiseQLError::Database {
            message:   format!("Failed to commit session-var transaction: {e}"),
            sql_state: e.code().map(|c| c.code().to_string()),
        })?;

        Ok(rows.iter().map(row_to_map).collect())
    }

    async fn execute_function_call(
        &self,
        function_name: &str,
        args: &[serde_json::Value],
    ) -> Result<Vec<std::collections::HashMap<String, serde_json::Value>>> {
        // Build: SELECT * FROM "fn_name"($1, $2, ...)
        // Use the standard identifier quoting utility so that schema-qualified
        // names like "benchmark.fn_update_user" are correctly split into
        // "benchmark"."fn_update_user" instead of being wrapped as a single
        // identifier.
        let quoted_fn = quote_postgres_identifier(function_name);
        let placeholders: Vec<String> = (1..=args.len()).map(|i| format!("${i}")).collect();
        let sql = format!("SELECT * FROM {quoted_fn}({})", placeholders.join(", "));

        let mut client = self.acquire_connection_with_retry().await?;

        // Convert serde_json::Value arguments to FlexParam for binding.
        //
        // serde_json::Value only accepts JSON/JSONB types; Option<String> only accepts
        // text-family types.  Neither works universally when the function signature
        // contains a mix of JSONB, UUID, INT4, and TEXT parameters.  FlexParam accepts
        // all PostgreSQL types and serialises each value in the correct binary wire
        // format for the server-resolved parameter type.
        let flex_args: Vec<FlexParam> = args
            .iter()
            .map(|v| match v {
                serde_json::Value::Null => FlexParam::Null,
                serde_json::Value::String(s) => FlexParam::Text(s.clone()),
                _ => FlexParam::Text(v.to_string()),
            })
            .collect();
        let params: Vec<&(dyn tokio_postgres::types::ToSql + Sync)> = flex_args
            .iter()
            .map(|v| v as &(dyn tokio_postgres::types::ToSql + Sync))
            .collect();

        // Parse/plan the statement once per connection and reuse it (deadpool's
        // statement cache); prepared before any transaction so the owned Statement
        // is usable inside it.
        let stmt = prepare_cached_stmt(&client, sql.as_str()).await?;

        if self.mutation_timing_enabled {
            // Wrap in a transaction so SET LOCAL scopes the variable to this call only.
            // `set_config(name, value, is_local)` with is_local=true is equivalent to
            // SET LOCAL and is parameterized to avoid SQL injection.
            let txn =
                client.build_transaction().start().await.map_err(|e| FraiseQLError::Database {
                    message:   format!("Failed to start mutation timing transaction: {e}"),
                    sql_state: e.code().map(|c| c.code().to_string()),
                })?;

            txn.execute(
                "SELECT set_config($1, clock_timestamp()::text, true)",
                &[&self.timing_variable_name],
            )
            .await
            .map_err(|e| FraiseQLError::Database {
                message:   format!("Failed to set mutation timing variable: {e}"),
                sql_state: e.code().map(|c| c.code().to_string()),
            })?;

            let rows: Vec<Row> = txn.query(&stmt, params.as_slice()).await.map_err(|e| {
                let detail = e.as_db_error().map_or("", |d| d.message());
                FraiseQLError::Database {
                    message:   format!("Function call {function_name} failed: {e}: {detail}"),
                    sql_state: e.code().map(|c| c.code().to_string()),
                }
            })?;

            txn.commit().await.map_err(|e| FraiseQLError::Database {
                message:   format!("Failed to commit mutation timing transaction: {e}"),
                sql_state: e.code().map(|c| c.code().to_string()),
            })?;

            let results: Vec<std::collections::HashMap<String, serde_json::Value>> =
                rows.iter().map(row_to_map).collect();

            Ok(results)
        } else {
            let rows: Vec<Row> = client.query(&stmt, params.as_slice()).await.map_err(|e| {
                let detail = e.as_db_error().map_or("", |d| d.message());
                FraiseQLError::Database {
                    message:   format!("Function call {function_name} failed: {e}: {detail}"),
                    sql_state: e.code().map(|c| c.code().to_string()),
                }
            })?;

            let results: Vec<std::collections::HashMap<String, serde_json::Value>> =
                rows.iter().map(row_to_map).collect();

            Ok(results)
        }
    }

    // PostgreSQL session variables are applied connection-affinely by the
    // `*_with_session` methods below: `set_config(..., true)` and the operation
    // share one transaction on one connection, so transaction-local GUCs are
    // visible to the function / view (fixes #329).

    async fn execute_function_call_with_session(
        &self,
        function_name: &str,
        args: &[serde_json::Value],
        session_vars: &[(&str, &str)],
    ) -> Result<Vec<std::collections::HashMap<String, serde_json::Value>>> {
        // Fast path: no session variables and no mutation timing => behave
        // exactly like execute_function_call (no transaction overhead, and
        // execute_function_call already opens its own txn when timing is on).
        if session_vars.is_empty() && !self.mutation_timing_enabled {
            return self.execute_function_call(function_name, args).await;
        }

        let quoted_fn = quote_postgres_identifier(function_name);
        let placeholders: Vec<String> = (1..=args.len()).map(|i| format!("${i}")).collect();
        let sql = format!("SELECT * FROM {quoted_fn}({})", placeholders.join(", "));

        // See execute_function_call for why FlexParam is required here.
        let flex_args: Vec<FlexParam> = args
            .iter()
            .map(|v| match v {
                serde_json::Value::Null => FlexParam::Null,
                serde_json::Value::String(s) => FlexParam::Text(s.clone()),
                _ => FlexParam::Text(v.to_string()),
            })
            .collect();
        let params: Vec<&(dyn tokio_postgres::types::ToSql + Sync)> = flex_args
            .iter()
            .map(|v| v as &(dyn tokio_postgres::types::ToSql + Sync))
            .collect();

        let mut client = self.acquire_connection_with_retry().await?;
        // Parse/plan once per connection (statement cache), before the txn.
        let stmt = prepare_cached_stmt(&client, sql.as_str()).await?;
        let txn =
            client.build_transaction().start().await.map_err(|e| FraiseQLError::Database {
                message:   format!("Failed to start session-var transaction: {e}"),
                sql_state: e.code().map(|c| c.code().to_string()),
            })?;

        // Apply session variables FIRST so the function body sees them.
        apply_session_vars(&txn, session_vars).await?;

        // If mutation timing is on, stamp the timing variable in the same txn.
        if self.mutation_timing_enabled {
            txn.execute(
                "SELECT set_config($1, clock_timestamp()::text, true)",
                &[&self.timing_variable_name],
            )
            .await
            .map_err(|e| FraiseQLError::Database {
                message:   format!("Failed to set mutation timing variable: {e}"),
                sql_state: e.code().map(|c| c.code().to_string()),
            })?;
        }

        let rows: Vec<Row> = txn.query(&stmt, params.as_slice()).await.map_err(|e| {
            let detail = e.as_db_error().map_or("", |d| d.message());
            FraiseQLError::Database {
                message:   format!("Function call {function_name} failed: {e}: {detail}"),
                sql_state: e.code().map(|c| c.code().to_string()),
            }
        })?;

        txn.commit().await.map_err(|e| FraiseQLError::Database {
            message:   format!("Failed to commit session-var transaction: {e}"),
            sql_state: e.code().map(|c| c.code().to_string()),
        })?;

        Ok(rows.iter().map(row_to_map).collect())
    }

    async fn execute_function_call_with_changelog(
        &self,
        function_name: &str,
        args: &[serde_json::Value],
        session_vars: &[(&str, &str)],
        changelog: Option<&crate::traits::ChangeLogWrite<'_>>,
    ) -> Result<Vec<std::collections::HashMap<String, serde_json::Value>>> {
        // No outbox write requested => identical to the session-affine path
        // (and inherits its no-session/no-timing fast path).
        let Some(changelog) = changelog else {
            return self
                .execute_function_call_with_session(function_name, args, session_vars)
                .await;
        };

        let quoted_fn = quote_postgres_identifier(function_name);
        // One statement: run the function once and INSERT its outbox row in the
        // same txn, atomically, with no extra connection acquire (Change Spine).
        let sql = build_changelog_cte_sql(&quoted_fn, args.len());

        // Function args first; then the threaded change-log envelope params —
        // object_type fallback ($n+1), modification_type verb ($n+2), the
        // tenant_id stamp ($n+3, bound against `::uuid`), the trace_id
        // ($n+4, plain text), and the schema_version ($n+5, plain text). Order
        // matches build_changelog_cte_sql's positional contract; appending the
        // envelope params keeps the SQL text stable for prepare_cached.
        let mut flex_args: Vec<FlexParam> = args
            .iter()
            .map(|v| match v {
                serde_json::Value::Null => FlexParam::Null,
                serde_json::Value::String(s) => FlexParam::Text(s.clone()),
                _ => FlexParam::Text(v.to_string()),
            })
            .collect();
        flex_args.push(FlexParam::Text(changelog.object_type.to_string()));
        flex_args.push(FlexParam::Text(changelog.modification_type.to_string()));
        // tenant_id: bound as text and serialised by FlexParam's UUID branch
        // (the `::uuid` cast pins the param type); None → SQL NULL.
        flex_args
            .push(changelog.tenant_id.map_or(FlexParam::Null, |t| FlexParam::Text(t.to_string())));
        // trace_id ($n+4): plain text, None → SQL NULL.
        flex_args
            .push(changelog.trace_id.map_or(FlexParam::Null, |t| FlexParam::Text(t.to_string())));
        // schema_version ($n+5): plain text, None → SQL NULL.
        flex_args.push(
            changelog
                .schema_version
                .map_or(FlexParam::Null, |s| FlexParam::Text(s.to_string())),
        );
        // trace_context ($n+6): JSON text bound against `::jsonb`, None → SQL NULL.
        flex_args.push(
            changelog
                .trace_context
                .map_or(FlexParam::Null, |s| FlexParam::Text(s.to_string())),
        );
        let params: Vec<&(dyn tokio_postgres::types::ToSql + Sync)> = flex_args
            .iter()
            .map(|v| v as &(dyn tokio_postgres::types::ToSql + Sync))
            .collect();

        let mut client = self.acquire_connection_with_retry().await?;
        // Parse/plan the (complex) CTE once per connection (statement cache) — this
        // is the dominant outbox hot-path cost; cached, the in-txn write is ~free.
        let stmt = prepare_cached_stmt(&client, sql.as_str()).await?;
        let txn =
            client.build_transaction().start().await.map_err(|e| FraiseQLError::Database {
                message:   format!("Failed to start change-log outbox transaction: {e}"),
                sql_state: e.code().map(|c| c.code().to_string()),
            })?;

        // Apply session variables FIRST so the function body sees them (and so
        // the started_at directive stamps the DB clock on this very txn).
        apply_session_vars(&txn, session_vars).await?;

        // If mutation timing is on, stamp the timing variable in the same txn.
        if self.mutation_timing_enabled {
            txn.execute(
                "SELECT set_config($1, clock_timestamp()::text, true)",
                &[&self.timing_variable_name],
            )
            .await
            .map_err(|e| FraiseQLError::Database {
                message:   format!("Failed to set mutation timing variable: {e}"),
                sql_state: e.code().map(|c| c.code().to_string()),
            })?;
        }

        // The outbox INSERT reads `fraiseql.started_at` with current_setting()
        // (no missing_ok), so the GUC MUST exist on this txn. The mutation runner
        // injects it via session_vars on the authenticated path; guarantee it on
        // every other path (e.g. an unauthenticated mutation that resolves no
        // session vars) so the duration computation never hits an unset
        // parameter and aborts the mutation.
        let started_at_set =
            session_vars.iter().any(|(name, _)| *name == crate::changelog::STARTED_AT_VAR)
                || (self.mutation_timing_enabled
                    && self.timing_variable_name == crate::changelog::STARTED_AT_VAR);
        if !started_at_set {
            txn.execute(
                "SELECT set_config($1, clock_timestamp()::text, true)",
                &[&crate::changelog::STARTED_AT_VAR],
            )
            .await
            .map_err(|e| FraiseQLError::Database {
                message:   format!("Failed to stamp change-log started_at: {e}"),
                sql_state: e.code().map(|c| c.code().to_string()),
            })?;
        }

        let rows: Vec<Row> = txn.query(&stmt, params.as_slice()).await.map_err(|e| {
            let detail = e.as_db_error().map_or("", |d| d.message());
            FraiseQLError::Database {
                message:   format!(
                    "Function call {function_name} (with change-log outbox) failed: {e}: {detail}"
                ),
                sql_state: e.code().map(|c| c.code().to_string()),
            }
        })?;

        txn.commit().await.map_err(|e| FraiseQLError::Database {
            message:   format!("Failed to commit change-log outbox transaction: {e}"),
            sql_state: e.code().map(|c| c.code().to_string()),
        })?;

        Ok(rows.iter().map(row_to_map).collect())
    }

    async fn execute_where_query_arc_with_session(
        &self,
        view: &str,
        where_clause: Option<&WhereClause>,
        limit: Option<u32>,
        offset: Option<u32>,
        order_by: Option<&[OrderByClause]>,
        session_vars: &[(&str, &str)],
    ) -> Result<Arc<Vec<JsonbValue>>> {
        if session_vars.is_empty() {
            return self.execute_where_query_arc(view, where_clause, limit, offset, order_by).await;
        }

        let (sql, typed_params) =
            build_where_select_sql_ordered(view, where_clause, limit, offset, order_by)?;
        let param_refs = crate::types::as_sql_param_refs(&typed_params);

        self.execute_raw_with_session(&sql, &param_refs, session_vars)
            .await
            .map(Arc::new)
            .map_err(|e| enrich_undefined_column_error(e, view, where_clause))
    }

    async fn execute_with_projection_arc_with_session(
        &self,
        request: &ProjectionRequest<'_>,
        session_vars: &[(&str, &str)],
    ) -> Result<Arc<Vec<JsonbValue>>> {
        if session_vars.is_empty() {
            return self.execute_with_projection_arc(request).await;
        }

        // No projection => behave like a plain WHERE query, matching
        // execute_with_projection_impl's fallback.
        let Some(projection) = request.projection else {
            return self
                .execute_where_query_arc_with_session(
                    request.view,
                    request.where_clause,
                    request.limit,
                    request.offset,
                    request.order_by,
                    session_vars,
                )
                .await;
        };

        let (sql, typed_params) = build_projection_select_sql(
            projection,
            request.view,
            request.where_clause,
            request.limit,
            request.offset,
            request.order_by,
        )?;
        let param_refs = crate::types::as_sql_param_refs(&typed_params);

        self.execute_raw_with_session(&sql, &param_refs, session_vars)
            .await
            .map(Arc::new)
    }

    async fn explain_query(
        &self,
        sql: &str,
        _params: &[serde_json::Value],
    ) -> Result<serde_json::Value> {
        // Defense-in-depth: reject multi-statement input even though this SQL is
        // compiler-generated. A semicolon would allow a second statement to be
        // appended to the EXPLAIN prefix.
        if sql.contains(';') {
            return Err(FraiseQLError::Validation {
                message: "EXPLAIN SQL must be a single statement".into(),
                path:    None,
            });
        }
        let explain_sql = format!("EXPLAIN (ANALYZE false, FORMAT JSON) {sql}");
        let client = self.acquire_connection_with_retry().await?;
        let rows: Vec<Row> =
            client
                .query(explain_sql.as_str(), &[])
                .await
                .map_err(|e| FraiseQLError::Database {
                    message:   format!("EXPLAIN failed: {e}"),
                    sql_state: e.code().map(|c| c.code().to_string()),
                })?;

        if let Some(row) = rows.first() {
            let plan: serde_json::Value = row.try_get(0).map_err(|e| FraiseQLError::Database {
                message:   format!("Failed to parse EXPLAIN output: {e}"),
                sql_state: None,
            })?;
            Ok(plan)
        } else {
            Ok(serde_json::Value::Null)
        }
    }

    async fn query_stats(&self, limit: u32) -> Result<Vec<crate::types::QueryStatEntry>> {
        self.pg_query_stats(limit).await
    }

    async fn query_stats_by_id(&self, id: &str) -> Result<Option<crate::types::QueryStatEntry>> {
        self.pg_query_stats_by_id(id).await
    }

    async fn reset_query_stats(&self) -> Result<()> {
        self.pg_reset_query_stats().await
    }
}

impl SupportsMutations for PostgresAdapter {}