diesel/query_dsl/
distinct_dsl.rs

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1use crate::dsl;
2#[cfg(feature = "postgres_backend")]
3use crate::expression::SelectableExpression;
4use crate::expression::TypedExpressionType;
5use crate::expression::ValidGrouping;
6use crate::query_builder::FromClause;
7use crate::query_builder::{AsQuery, SelectStatement};
8use crate::query_source::Table;
9use crate::Expression;
10
11/// The `distinct` method
12///
13/// This trait should not be relied on directly by most apps. Its behavior is
14/// provided by [`QueryDsl`]. However, you may need a where clause on this trait
15/// to call `distinct` from generic code.
16///
17/// [`QueryDsl`]: crate::QueryDsl
18pub trait DistinctDsl {
19    /// The type returned by `.distinct`
20    type Output;
21
22    /// See the trait documentation.
23    fn distinct(self) -> dsl::Distinct<Self>;
24}
25
26impl<T> DistinctDsl for T
27where
28    T: Table + AsQuery<Query = SelectStatement<FromClause<T>>>,
29    T::DefaultSelection: Expression<SqlType = T::SqlType> + ValidGrouping<()>,
30    T::SqlType: TypedExpressionType,
31{
32    type Output = dsl::Distinct<SelectStatement<FromClause<T>>>;
33
34    fn distinct(self) -> dsl::Distinct<SelectStatement<FromClause<T>>> {
35        self.as_query().distinct()
36    }
37}
38
39/// The `distinct_on` method
40///
41/// This trait should not be relied on directly by most apps. Its behavior is
42/// provided by [`QueryDsl`]. However, you may need a where clause on this trait
43/// to call `distinct_on` from generic code.
44///
45/// [`QueryDsl`]: crate::QueryDsl
46#[cfg(feature = "postgres_backend")]
47pub trait DistinctOnDsl<Selection> {
48    /// The type returned by `.distinct_on`
49    type Output;
50
51    /// See the trait documentation
52    fn distinct_on(self, selection: Selection) -> dsl::DistinctOn<Self, Selection>;
53}
54
55#[cfg(feature = "postgres_backend")]
56impl<T, Selection> DistinctOnDsl<Selection> for T
57where
58    Selection: SelectableExpression<T>,
59    T: Table + AsQuery<Query = SelectStatement<FromClause<T>>>,
60    SelectStatement<FromClause<T>>: DistinctOnDsl<Selection>,
61    T::DefaultSelection: Expression<SqlType = T::SqlType> + ValidGrouping<()>,
62    T::SqlType: TypedExpressionType,
63{
64    type Output = dsl::DistinctOn<SelectStatement<FromClause<T>>, Selection>;
65
66    fn distinct_on(self, selection: Selection) -> dsl::DistinctOn<Self, Selection> {
67        self.as_query().distinct_on(selection)
68    }
69}
diesel/query_dsl/distinct_dsl.rs

diesel/query_dsl/
distinct_dsl.rs
