diesel/expression/
subselect.rs

1use std::marker::PhantomData;
2
3use crate::expression::array_comparison::MaybeEmpty;
4use crate::expression::*;
5use crate::query_builder::*;
6use crate::result::QueryResult;
7
8#[derive(Debug, Copy, Clone, QueryId)]
9pub struct Subselect<T, ST> {
10    values: T,
11    _sql_type: PhantomData<ST>,
12}
13
14impl<T, ST> Subselect<T, ST> {
15    pub(crate) fn new(values: T) -> Self {
16        Self {
17            values,
18            _sql_type: PhantomData,
19        }
20    }
21}
22
23impl<T: SelectQuery, ST> Expression for Subselect<T, ST>
24where
25    ST: SqlType + TypedExpressionType,
26{
27    type SqlType = ST;
28}
29
30impl<T, ST> MaybeEmpty for Subselect<T, ST> {
31    fn is_empty(&self) -> bool {
32        false
33    }
34}
35
36impl<T, ST, QS> SelectableExpression<QS> for Subselect<T, ST>
37where
38    Subselect<T, ST>: AppearsOnTable<QS>,
39    T: ValidSubselect<QS>,
40{
41}
42
43impl<T, ST, QS> AppearsOnTable<QS> for Subselect<T, ST>
44where
45    Subselect<T, ST>: Expression,
46    T: ValidSubselect<QS>,
47{
48}
49
50// FIXME: This probably isn't sound. The subselect can reference columns from
51// the outer query, and is affected by the `GROUP BY` clause of the outer query
52// identically to using it outside of a subselect
53impl<T, ST, GB> ValidGrouping<GB> for Subselect<T, ST> {
54    type IsAggregate = is_aggregate::Never;
55}
56
57impl<T, ST, DB> QueryFragment<DB> for Subselect<T, ST>
58where
59    DB: Backend,
60    T: QueryFragment<DB>,
61{
62    fn walk_ast<'b>(&'b self, mut out: AstPass<'_, 'b, DB>) -> QueryResult<()> {
63        self.values.walk_ast(out.reborrow())?;
64        Ok(())
65    }
66}
67
68pub trait ValidSubselect<QS> {}