diesel/expression/
nullable.rs

1use crate::backend::DieselReserveSpecialization;
2use crate::expression::*;
3use crate::query_builder::*;
4use crate::query_source::joins::ToInnerJoin;
5use crate::result::QueryResult;
6use crate::sql_types::{DieselNumericOps, IntoNullable};
7
8#[doc(hidden)] // This is used by the `table!` macro internally
9#[derive(Debug, Copy, Clone, DieselNumericOps, ValidGrouping)]
10pub struct Nullable<T>(pub(crate) T);
11
12impl<T> Nullable<T> {
13    pub(crate) fn new(expr: T) -> Self {
14        Nullable(expr)
15    }
16}
17
18impl<T> Expression for Nullable<T>
19where
20    T: Expression,
21    T::SqlType: IntoNullable,
22    <T::SqlType as IntoNullable>::Nullable: TypedExpressionType,
23{
24    type SqlType = <T::SqlType as IntoNullable>::Nullable;
25}
26
27impl<T, DB> QueryFragment<DB> for Nullable<T>
28where
29    DB: Backend + DieselReserveSpecialization,
30    T: QueryFragment<DB>,
31{
32    fn walk_ast<'b>(&'b self, pass: AstPass<'_, 'b, DB>) -> QueryResult<()> {
33        self.0.walk_ast(pass)
34    }
35}
36
37impl<T, QS> AppearsOnTable<QS> for Nullable<T>
38where
39    T: AppearsOnTable<QS>,
40    Nullable<T>: Expression,
41{
42}
43
44impl<T: QueryId> QueryId for Nullable<T> {
45    type QueryId = T::QueryId;
46
47    const HAS_STATIC_QUERY_ID: bool = T::HAS_STATIC_QUERY_ID;
48}
49
50impl<T, QS> SelectableExpression<QS> for Nullable<T>
51where
52    Self: AppearsOnTable<QS>,
53    QS: ToInnerJoin,
54    T: SelectableExpression<QS::InnerJoin>,
55{
56}
57
58impl<T> SelectableExpression<NoFromClause> for Nullable<T> where Self: AppearsOnTable<NoFromClause> {}