diesel/query_dsl/
positional_order_dsl.rs

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1use crate::backend::{Backend, DieselReserveSpecialization};
2use crate::expression::helper_types::{Asc, Desc};
3use crate::query_builder::combination_clause::CombinationClause;
4use crate::query_builder::{AstPass, Query, QueryFragment, QueryId};
5use crate::{QueryResult, RunQueryDsl};
6
7/// This trait is not yet part of Diesel's public API. It may change in the
8/// future without a major version bump.
9///
10/// This trait exists as a stop-gap for users who need to order by column position
11/// in their queries, so that they are not forced to drop entirely to raw SQL. The
12/// arguments to `positional_order_by` are not checked, nor is the select statement
13/// forced to be valid.
14pub trait PositionalOrderDsl<Expr: Order>: Sized {
15    fn positional_order_by(self, expr: Expr) -> PositionalOrderClause<Self, Expr::Fragment> {
16        PositionalOrderClause {
17            source: self,
18            expr: expr.into_fragment(),
19        }
20    }
21}
22
23#[derive(Debug, Clone, Copy, QueryId)]
24pub struct PositionalOrderClause<Source, Expr> {
25    source: Source,
26    expr: Expr,
27}
28
29impl<Combinator, Rule, Source, Rhs, Expr: Order> PositionalOrderDsl<Expr>
30    for CombinationClause<Combinator, Rule, Source, Rhs>
31{
32}
33
34impl<Source, Expr> Query for PositionalOrderClause<Source, Expr>
35where
36    Source: Query,
37{
38    type SqlType = Source::SqlType;
39}
40
41impl<Source, Expr, Conn> RunQueryDsl<Conn> for PositionalOrderClause<Source, Expr> {}
42
43impl<Source, Expr, DB> QueryFragment<DB> for PositionalOrderClause<Source, Expr>
44where
45    DB: Backend + DieselReserveSpecialization,
46    Source: QueryFragment<DB>,
47    Expr: QueryFragment<DB>,
48{
49    fn walk_ast<'b>(&'b self, mut pass: AstPass<'_, 'b, DB>) -> QueryResult<()> {
50        self.source.walk_ast(pass.reborrow())?;
51        pass.push_sql(" ORDER BY ");
52        self.expr.walk_ast(pass)
53    }
54}
55
56#[derive(Debug, Clone, Copy, QueryId)]
57pub struct OrderColumn(u32);
58
59impl<DB: Backend> QueryFragment<DB> for OrderColumn {
60    fn walk_ast<'b>(&'b self, mut pass: AstPass<'_, 'b, DB>) -> QueryResult<()> {
61        pass.push_sql(&self.0.to_string());
62        Ok(())
63    }
64}
65
66impl From<u32> for OrderColumn {
67    fn from(order: u32) -> Self {
68        OrderColumn(order)
69    }
70}
71
72pub trait IntoOrderColumn: Into<OrderColumn> {
73    fn asc(self) -> Asc<OrderColumn> {
74        Asc { expr: self.into() }
75    }
76    fn desc(self) -> Desc<OrderColumn> {
77        Desc { expr: self.into() }
78    }
79}
80
81impl<T> IntoOrderColumn for T where T: Into<OrderColumn> {}
82
83pub trait Order: Copy {
84    type Fragment;
85
86    fn into_fragment(self) -> Self::Fragment;
87}
88
89impl<T: Into<OrderColumn> + Copy> Order for T {
90    type Fragment = OrderColumn;
91
92    fn into_fragment(self) -> Self::Fragment {
93        self.into()
94    }
95}
96
97impl Order for Asc<OrderColumn> {
98    type Fragment = Asc<OrderColumn>;
99
100    fn into_fragment(self) -> Self::Fragment {
101        self
102    }
103}
104
105impl Order for Desc<OrderColumn> {
106    type Fragment = Desc<OrderColumn>;
107
108    fn into_fragment(self) -> Self::Fragment {
109        self
110    }
111}
112
113macro_rules! impl_order_for_all_tuples {
114    ($(
115        $unused1:tt {
116            $(($idx:tt) -> $T:ident, $unused2:ident, $unused3:tt,)+
117        }
118    )+) => {
119        $(
120            impl<$($T: Order),+> Order for ($($T,)+) {
121                type Fragment = ($(<$T as Order>::Fragment,)+);
122
123                fn into_fragment(self) -> Self::Fragment {
124                    ($(self.$idx.into_fragment(),)+)
125                }
126            }
127        )+
128    };
129}
130
131diesel_derives::__diesel_for_each_tuple!(impl_order_for_all_tuples);
diesel/query_dsl/positional_order_dsl.rs

diesel/query_dsl/
positional_order_dsl.rs
