1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130

use crate::backend::DieselReserveSpecialization;
use crate::expression::grouped::Grouped;
use crate::expression::operators::Eq;
use crate::expression::AppearsOnTable;
use crate::query_builder::*;
use crate::query_source::{Column, QuerySource};
use crate::Table;

/// Types which can be passed to
/// [`update.set`](UpdateStatement::set()).
///
/// This trait can be [derived](derive@AsChangeset)
pub trait AsChangeset {
    /// The table which `Self::Changeset` will be updating
    type Target: QuerySource;

    /// The update statement this type represents
    type Changeset;

    /// Convert `self` into the actual update statement being executed
    // This method is part of our public API
    // we won't change it to just appease clippy
    #[allow(clippy::wrong_self_convention)]
    fn as_changeset(self) -> Self::Changeset;
}

// This is a false positive, we reexport it later
#[allow(unreachable_pub)]
#[doc(inline)]
pub use diesel_derives::AsChangeset;

impl<T: AsChangeset> AsChangeset for Option<T> {
    type Target = T::Target;
    type Changeset = Option<T::Changeset>;

    fn as_changeset(self) -> Self::Changeset {
        self.map(AsChangeset::as_changeset)
    }
}

impl<Left, Right> AsChangeset for Eq<Left, Right>
where
    Left: AssignmentTarget,
    Right: AppearsOnTable<Left::Table>,
{
    type Target = Left::Table;
    type Changeset = Assign<<Left as AssignmentTarget>::QueryAstNode, Right>;

    fn as_changeset(self) -> Self::Changeset {
        Assign {
            target: self.left.into_target(),
            expr: self.right,
        }
    }
}

impl<Left, Right> AsChangeset for Grouped<Eq<Left, Right>>
where
    Eq<Left, Right>: AsChangeset,
{
    type Target = <Eq<Left, Right> as AsChangeset>::Target;

    type Changeset = <Eq<Left, Right> as AsChangeset>::Changeset;

    fn as_changeset(self) -> Self::Changeset {
        self.0.as_changeset()
    }
}

#[derive(Debug, Clone, Copy, QueryId)]
pub struct Assign<Target, Expr> {
    target: Target,
    expr: Expr,
}

impl<T, U, DB> QueryFragment<DB> for Assign<T, U>
where
    DB: Backend,
    T: QueryFragment<DB>,
    U: QueryFragment<DB>,
{
    fn walk_ast<'b>(&'b self, mut out: AstPass<'_, 'b, DB>) -> QueryResult<()> {
        QueryFragment::walk_ast(&self.target, out.reborrow())?;
        out.push_sql(" = ");
        QueryFragment::walk_ast(&self.expr, out.reborrow())
    }
}

/// Represents the left hand side of an assignment expression for an
/// assignment in [AsChangeset]. The vast majority of the time, this will
/// be a [Column]. However, in certain database backends, it's possible to
/// assign to an expression. For example, in Postgres, it's possible to
/// "UPDATE TABLE SET array_column\[1\] = 'foo'".
pub trait AssignmentTarget {
    /// Table the assignment is to
    type Table: Table;
    /// A wrapper around a type to assign to (this wrapper should implement
    /// [QueryFragment]).
    type QueryAstNode;

    /// Move this in to the AST node which should implement [QueryFragment].
    fn into_target(self) -> Self::QueryAstNode;
}

/// Represents a `Column` as an `AssignmentTarget`. The vast majority of
/// targets in an update statement will be `Column`s.
#[derive(Debug, Clone, Copy)]
pub struct ColumnWrapperForUpdate<C>(pub C);

impl<DB, C> QueryFragment<DB> for ColumnWrapperForUpdate<C>
where
    DB: Backend + DieselReserveSpecialization,
    C: Column,
{
    fn walk_ast<'b>(&'b self, mut out: AstPass<'_, 'b, DB>) -> QueryResult<()> {
        out.push_identifier(C::NAME)
    }
}

impl<C> AssignmentTarget for C
where
    C: Column,
{
    type Table = C::Table;
    type QueryAstNode = ColumnWrapperForUpdate<C>;

    fn into_target(self) -> Self::QueryAstNode {
        ColumnWrapperForUpdate(self)
    }
}