vantage_table/table/impls/

spec.rs

//! Lowering a YAML [`VistaSpec`] onto a table:
//! the steps every driver factory shares. Type mapping and driver blocks stay
//! with the driver, passed in as `build` functions.

use std::sync::Arc;

use indexmap::IndexMap;
use vantage_core::{Result, VantageError, error};
use vantage_expressions::{Expressive, SelectableDataSource};
use vantage_types::{EmptyEntity, Entity};
use vantage_vista::{
    ColumnFlag, ColumnSpec, JoinKey, ReferenceKind, ReferenceSugar, SpecResolver, VistaSpec,
};

use crate::{source::SelectSource, table::Table, traits::table_source::TableSource};

/// Rebuilds a referenced table from its spec, a data source and the resolver.
type SpecTableBuilder<S, T> =
    fn(&S, T, Option<Arc<dyn SpecResolver<S>>>) -> Result<Table<T, EmptyEntity>>;

impl<T: TableSource, E: Entity<T::Value>> Table<T, E> {
    /// Add one spec column. A `lazy:` column becomes a computed column;
    /// any other is built by `build` (unless the table already has it, as a
    /// derived table may) and registered as a title when flagged `title`.
    /// Returns whether the column is stored.
    pub fn add_spec_column<C>(
        &mut self,
        name: &str,
        spec: &ColumnSpec<C>,
        build: impl FnOnce(&str, &ColumnSpec<C>) -> Result<T::Column<T::AnyType>>,
    ) -> Result<bool> {
        if self.add_lazy_spec_column(spec, name)? {
            return Ok(false);
        }
        if !self.columns.contains_key(name) {
            self.add_column(build(name, spec)?);
        }
        if spec.has_flag(ColumnFlag::Title) {
            self.add_title_field(name);
        }
        Ok(true)
    }

    /// [`add_spec_column`](Self::add_spec_column) for each column, in order.
    pub fn add_spec_columns<C>(
        &mut self,
        columns: &IndexMap<String, ColumnSpec<C>>,
        build: impl Fn(&str, &ColumnSpec<C>) -> Result<T::Column<T::AnyType>>,
    ) -> Result<()> {
        for (name, spec) in columns {
            self.add_spec_column(name, spec, &build)?;
        }
        Ok(())
    }

    /// Mark the spec's id column as the id field. Errors when the spec
    /// doesn't declare that column.
    pub fn set_spec_id_field(&mut self, id: &str) -> Result<()> {
        if !self.columns.contains_key(id) {
            return Err(error!("id column not present in spec.columns", id = id));
        }
        self.set_id_field(id);
        Ok(())
    }
}

impl<T: TableSource + 'static, E: Entity<T::Value> + 'static> Table<T, E>
where
    T::Value: Into<ciborium::Value> + From<ciborium::Value>,
    T::Id: std::fmt::Display + From<String>,
{
    /// Register every join `spec` declares as `with_one` / `with_many`: its
    /// `references:` entries, then the column-level `references:` sugar
    /// (see [`spec_references`]).
    ///
    /// At traversal time the reference asks `resolver` for the target's
    /// current spec and rebuilds it with `build`. Without a resolver, or on a
    /// miss or a build error, the target is a column-less `Table::new(target)`
    /// and the next query against it fails. A contained kind is an error:
    /// contained relations are declared under `contained:`.
    pub fn with_spec_references<X, C, R, S: 'static>(
        mut self,
        spec: &VistaSpec<X, C, R>,
        resolver: Option<Arc<dyn SpecResolver<S>>>,
        build: SpecTableBuilder<S, T>,
    ) -> Result<Self> {
        for (relation, reference) in &spec.references {
            let foreign_key = reference.foreign_key(relation);
            self = self.with_spec_join(
                relation,
                &reference.table,
                reference.kind,
                &foreign_key,
                resolver.clone(),
                build,
            )?;
        }
        for (column, sugar) in column_references(spec) {
            let (target, kind, foreign_key) = match sugar {
                ReferenceSugar::Sugar(target) => (target, ReferenceKind::HasOne, column.clone()),
                ReferenceSugar::Full(r) => (&r.table, r.kind, r.foreign_key(column)),
                _ => return Err(unknown_sugar(column)),
            };
            self =
                self.with_spec_join(column, target, kind, &foreign_key, resolver.clone(), build)?;
        }
        Ok(self)
    }

    fn with_spec_join<S: 'static>(
        self,
        relation: &str,
        target: &str,
        kind: ReferenceKind,
        foreign_key: &str,
        resolver: Option<Arc<dyn SpecResolver<S>>>,
        build: SpecTableBuilder<S, T>,
    ) -> Result<Self> {
        let target = target.to_string();
        let build_target = move |source: T| -> Table<T, EmptyEntity> {
            if let Some(r) = &resolver
                && let Some(spec) = r.resolve(&target)
                && let Ok(table) = build(&spec, source.clone(), Some(r.clone()))
            {
                return table;
            }
            Table::new(target.clone(), source)
        };
        match kind {
            ReferenceKind::HasOne => Ok(self.with_one(relation, foreign_key, build_target)),
            ReferenceKind::HasMany => Ok(self.with_many(relation, foreign_key, build_target)),
            _ => Err(error!(
                "references: entries must be has_one or has_many",
                relation = relation
            )),
        }
    }
}

/// Every join `spec` declares, as Vista references: each `references:`
/// entry, then each column-level `references:` not shadowed by an entry of
/// the same name. The sugar names its relation after the column, which is
/// also its foreign key: `bakery: { references: bakery }` is a has-one
/// keyed by `bakery`. `source_id` is the column a `has_many` reads from
/// this table's rows.
pub fn spec_references<X, C, R>(
    spec: &VistaSpec<X, C, R>,
    source_id: &str,
) -> Result<Vec<vantage_vista::Reference>> {
    let mut out = Vec::with_capacity(spec.references.len());
    for (relation, reference) in &spec.references {
        out.push(reference.to_reference(relation, source_id)?);
    }
    for (column, sugar) in column_references(spec) {
        out.push(match sugar {
            ReferenceSugar::Sugar(target) => {
                vantage_vista::Reference::has_one(column, target, JoinKey::to_target_id(column))
            }
            ReferenceSugar::Full(r) => r.to_reference(column, source_id)?,
            _ => return Err(unknown_sugar(column)),
        });
    }
    Ok(out)
}

fn unknown_sugar(column: &str) -> VantageError {
    error!(
        "column references: takes a table name or a full reference",
        column = column
    )
}

/// The column-level `references:` of `spec` that no `references:` entry
/// shadows, keyed by column.
fn column_references<X, C, R>(
    spec: &VistaSpec<X, C, R>,
) -> impl Iterator<Item = (&String, &ReferenceSugar)> {
    spec.columns.iter().filter_map(|(column, col)| {
        let sugar = col.references.as_ref()?;
        (!spec.references.contains_key(column)).then_some((column, sugar))
    })
}

// Same bounds as `Table::derive_from`, which this builds on.
impl<T, E, V, Cond, S> Table<T, E>
where
    T: SelectableDataSource<V, Cond, Select = S>
        + TableSource<Value = V, Condition = Cond, Source = SelectSource<S>>,
    V: Clone + Send + Sync + 'static + From<String>,
    Cond: Clone + Send + Sync + 'static,
    S: Expressive<V> + Clone,
    E: Entity<V>,
{
    /// Lower a `base:` spec: a table over `select` (the base's select, possibly
    /// transformed) that inherits the listed base columns and relations, adds
    /// the spec's own columns (aggregate outputs, say) and contained
    /// relations, and keeps the base's id unless the spec names one.
    pub fn derive_from_spec<E2: Entity<V> + 'static, X, C, R>(
        base: &Table<T, E2>,
        spec: &VistaSpec<X, C, R>,
        select: S,
        inherit_columns: &[String],
        inherit_relations: &[String],
        build_column: impl Fn(&str, &ColumnSpec<C>) -> Result<T::Column<T::AnyType>>,
    ) -> Result<Self>
    where
        T: 'static,
        E: 'static,
    {
        let columns: Vec<&str> = inherit_columns.iter().map(String::as_str).collect();
        let relations: Vec<&str> = inherit_relations.iter().map(String::as_str).collect();
        let mut table = Self::derive_from(
            base,
            spec.name.clone(),
            move |_| select,
            &columns,
            &relations,
        );
        table.add_spec_columns(&spec.columns, &build_column)?;
        if let Some(id) = &spec.id_column {
            table.set_id_field(id);
        }
        table.with_contained_specs(&spec.contained, build_column)
    }
}