diesel/query_builder/
select_clause.rs

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1use super::from_clause::AsQuerySource;
2use crate::expression::{Expression, SelectableExpression};
3use crate::query_builder::*;
4use crate::query_source::QuerySource;
5
6#[doc(hidden)]
7pub struct DefaultSelectClause<QS: AsQuerySource> {
8    default_selection: <QS::QuerySource as QuerySource>::DefaultSelection,
9}
10
11impl<QS> std::fmt::Debug for DefaultSelectClause<QS>
12where
13    QS: AsQuerySource,
14    <QS::QuerySource as QuerySource>::DefaultSelection: std::fmt::Debug,
15{
16    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
17        f.debug_struct("DefaultSelectClause")
18            .field("default_selection", &self.default_selection)
19            .finish()
20    }
21}
22
23impl<QS> Clone for DefaultSelectClause<QS>
24where
25    QS: AsQuerySource,
26    <QS::QuerySource as QuerySource>::DefaultSelection: Clone,
27{
28    fn clone(&self) -> Self {
29        Self {
30            default_selection: self.default_selection.clone(),
31        }
32    }
33}
34
35impl<QS> Copy for DefaultSelectClause<QS>
36where
37    QS: AsQuerySource,
38    <QS::QuerySource as QuerySource>::DefaultSelection: Copy,
39{
40}
41
42impl<QS: AsQuerySource> DefaultSelectClause<QS> {
43    pub(crate) fn new(qs: &QS) -> Self {
44        Self {
45            default_selection: qs.as_query_source().default_selection(),
46        }
47    }
48}
49
50impl<QS> QueryId for DefaultSelectClause<QS>
51where
52    QS: AsQuerySource,
53    <QS::QuerySource as QuerySource>::DefaultSelection: QueryId,
54{
55    type QueryId = <<QS::QuerySource as QuerySource>::DefaultSelection as QueryId>::QueryId;
56
57    const HAS_STATIC_QUERY_ID: bool =
58        <<QS::QuerySource as QuerySource>::DefaultSelection as QueryId>::HAS_STATIC_QUERY_ID;
59}
60
61#[derive(Debug, Clone, Copy, QueryId)]
62pub struct SelectClause<T>(pub T);
63
64/// Specialised variant of `Expression` for select clause types
65///
66/// The difference to the normal `Expression` trait is the query source (`QS`)
67/// generic type parameter. This allows to access the query source in generic code.
68#[cfg_attr(
69    feature = "i-implement-a-third-party-backend-and-opt-into-breaking-changes",
70    cfg(feature = "i-implement-a-third-party-backend-and-opt-into-breaking-changes")
71)]
72pub trait SelectClauseExpression<QS> {
73    /// The expression represented by the given select clause
74    type Selection;
75    /// SQL type of the select clause
76    type SelectClauseSqlType;
77}
78
79impl<T, QS> SelectClauseExpression<FromClause<QS>> for SelectClause<T>
80where
81    QS: QuerySource,
82    T: SelectableExpression<QS>,
83{
84    type Selection = T;
85    type SelectClauseSqlType = T::SqlType;
86}
87
88impl<T> SelectClauseExpression<NoFromClause> for SelectClause<T>
89where
90    T: SelectableExpression<NoFromClause>,
91{
92    type Selection = T;
93    type SelectClauseSqlType = T::SqlType;
94}
95
96impl<QS> SelectClauseExpression<FromClause<QS>> for DefaultSelectClause<FromClause<QS>>
97where
98    QS: QuerySource,
99{
100    type Selection = QS::DefaultSelection;
101    type SelectClauseSqlType = <Self::Selection as Expression>::SqlType;
102}
103
104impl<T, DB> QueryFragment<DB> for SelectClause<T>
105where
106    DB: Backend,
107    T: QueryFragment<DB>,
108{
109    fn walk_ast<'b>(&'b self, pass: AstPass<'_, 'b, DB>) -> QueryResult<()> {
110        self.0.walk_ast(pass)
111    }
112}
113
114impl<QS, DB> QueryFragment<DB> for DefaultSelectClause<QS>
115where
116    DB: Backend,
117    QS: AsQuerySource,
118    <QS::QuerySource as QuerySource>::DefaultSelection: QueryFragment<DB>,
119{
120    fn walk_ast<'b>(&'b self, pass: AstPass<'_, 'b, DB>) -> QueryResult<()> {
121        self.default_selection.walk_ast(pass)
122    }
123}
diesel/query_builder/select_clause.rs

diesel/query_builder/
select_clause.rs
