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//! SQL `CAST(expr AS sql_type)` expression support | ||
use crate::expression::{AppearsOnTable, Expression, SelectableExpression, ValidGrouping}; | ||
use crate::query_source::aliasing::{AliasSource, FieldAliasMapper}; | ||
use crate::result::QueryResult; | ||
use crate::{query_builder, query_source, sql_types}; | ||
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use std::marker::PhantomData; | ||
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pub(crate) mod private { | ||
use super::*; | ||
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#[derive(Debug, Clone, Copy, diesel::query_builder::QueryId, sql_types::DieselNumericOps)] | ||
pub struct Cast<E, ST> { | ||
pub(super) expr: E, | ||
pub(super) sql_type: PhantomData<ST>, | ||
} | ||
} | ||
pub(crate) use private::Cast; | ||
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impl<E, ST> Cast<E, ST> { | ||
pub(crate) fn new(expr: E) -> Self { | ||
Self { | ||
expr, | ||
sql_type: PhantomData, | ||
} | ||
} | ||
} | ||
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impl<E, ST, GroupByClause> ValidGrouping<GroupByClause> for Cast<E, ST> | ||
where | ||
E: ValidGrouping<GroupByClause>, | ||
{ | ||
type IsAggregate = E::IsAggregate; | ||
} | ||
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impl<E, ST, QS> SelectableExpression<QS> for Cast<E, ST> | ||
where | ||
Cast<E, ST>: AppearsOnTable<QS>, | ||
E: SelectableExpression<QS>, | ||
{ | ||
} | ||
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impl<E, ST, QS> AppearsOnTable<QS> for Cast<E, ST> | ||
where | ||
Cast<E, ST>: Expression, | ||
E: AppearsOnTable<QS>, | ||
{ | ||
} | ||
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impl<E, ST> Expression for Cast<E, ST> | ||
where | ||
E: Expression, | ||
ST: sql_types::SingleValue, | ||
{ | ||
type SqlType = ST; | ||
} | ||
impl<E, ST, DB> query_builder::QueryFragment<DB> for Cast<E, ST> | ||
where | ||
E: query_builder::QueryFragment<DB>, | ||
DB: diesel::backend::Backend, | ||
ST: KnownCastSqlTypeName<DB>, | ||
{ | ||
fn walk_ast<'b>(&'b self, mut out: query_builder::AstPass<'_, 'b, DB>) -> QueryResult<()> { | ||
out.push_sql("CAST("); | ||
self.expr.walk_ast(out.reborrow())?; | ||
out.push_sql(" AS "); | ||
out.push_sql(ST::sql_type_name()); | ||
out.push_sql(")"); | ||
Ok(()) | ||
} | ||
} | ||
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/// We know what to write as `sql_type` in the `CAST(expr AS sql_type)` SQL for | ||
/// `Self` | ||
/// | ||
/// That is what is returned by `Self::sql_type_name()` | ||
#[diagnostic::on_unimplemented( | ||
note = "In order to use `CAST`, it is necessary that Diesel knows how to express the name \ | ||
of this type in the given backend.", | ||
note = "This can be PRed into Diesel if the type is a standard SQL type." | ||
)] | ||
pub trait KnownCastSqlTypeName<DB> { | ||
/// What to write as `sql_type` in the `CAST(expr AS sql_type)` SQL for | ||
/// `Self` | ||
fn sql_type_name() -> &'static str; | ||
} | ||
impl<ST, DB> KnownCastSqlTypeName<DB> for sql_types::Nullable<ST> | ||
where | ||
ST: KnownCastSqlTypeName<DB>, | ||
{ | ||
fn sql_type_name() -> &'static str { | ||
<ST as KnownCastSqlTypeName<DB>>::sql_type_name() | ||
} | ||
} | ||
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macro_rules! type_name { | ||
($($backend: ty: $backend_feature: literal { $($type: ident => $val: literal,)+ })*) => { | ||
$( | ||
$( | ||
#[cfg(feature = $backend_feature)] | ||
impl KnownCastSqlTypeName<$backend> for sql_types::$type { | ||
fn sql_type_name() -> &'static str { | ||
$val | ||
} | ||
} | ||
)* | ||
)* | ||
}; | ||
} | ||
type_name! { | ||
diesel::pg::Pg: "postgres_backend" { | ||
Int4 => "int4", | ||
Int8 => "int8", | ||
Text => "text", | ||
} | ||
diesel::mysql::Mysql: "mysql_backend" { | ||
Int4 => "integer", | ||
Int8 => "integer", | ||
Text => "text", | ||
} | ||
diesel::sqlite::Sqlite: "sqlite" { | ||
Int4 => "integer", | ||
Int8 => "bigint", | ||
Text => "text", | ||
} | ||
} | ||
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impl<S, E, ST> FieldAliasMapper<S> for Cast<E, ST> | ||
where | ||
S: AliasSource, | ||
E: FieldAliasMapper<S>, | ||
{ | ||
type Out = Cast<<E as FieldAliasMapper<S>>::Out, ST>; | ||
fn map(self, alias: &query_source::Alias<S>) -> Self::Out { | ||
Cast { | ||
expr: self.expr.map(alias), | ||
sql_type: self.sql_type, | ||
} | ||
} | ||
} | ||
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/// Marker trait: this SQL type (`Self`) can be casted to the target SQL type | ||
/// (`ST`) using `CAST(expr AS target_sql_type)` | ||
pub trait CastsTo<ST> {} | ||
impl<ST1, ST2> CastsTo<sql_types::Nullable<ST2>> for sql_types::Nullable<ST1> where ST1: CastsTo<ST2> | ||
{} | ||
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impl CastsTo<sql_types::Int8> for sql_types::Int4 {} | ||
impl CastsTo<sql_types::Int4> for sql_types::Int8 {} | ||
impl CastsTo<sql_types::Text> for sql_types::Int4 {} | ||
impl CastsTo<sql_types::Text> for sql_types::Int8 {} |
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