diesel/query_dsl/
select_dsl.rs

1use crate::expression::Expression;
2use crate::query_source::Table;
3
4/// The `select` method
5///
6/// This trait should not be relied on directly by most apps. Its behavior is
7/// provided by [`QueryDsl`]. However, you may need a where clause on this trait
8/// to call `select` from generic code.
9///
10/// [`QueryDsl`]: crate::QueryDsl
11pub trait SelectDsl<Selection: Expression> {
12    // FIXME: Once we've refactored the `impl Expression` on `SelectStatement`
13    // to not conditionally be `sql_types::Array`, it is probably worthwhile to
14    // add a `: Expression<SqlType = Selection::SqlType>` bound here.
15    /// The type returned by `.select`
16    type Output;
17
18    /// See the trait documentation
19    fn select(self, selection: Selection) -> Self::Output;
20}
21
22impl<T, Selection> SelectDsl<Selection> for T
23where
24    Selection: Expression,
25    T: Table,
26    T::Query: SelectDsl<Selection>,
27{
28    type Output = <T::Query as SelectDsl<Selection>>::Output;
29
30    fn select(self, selection: Selection) -> Self::Output {
31        self.as_query().select(selection)
32    }
33}