Merge pull request #3722 from weiznich/fix/make_alias_syntax_configur…

…able Allow to configure the used alias syntax
diesel-rs · Jul 31, 2023 · b479f24 · b479f24
2 parents 082fb7d + e632a7c
commit b479f24
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Showing 6 changed files with 49 additions and 1 deletion.
diff --git a/diesel/src/backend.rs b/diesel/src/backend.rs
@@ -306,6 +306,17 @@ pub trait SqlDialect: self::private::TrustedBackend {
         doc = "See [`sql_dialect::select_statement_syntax`] for provided default implementations"
     )]
     type SelectStatementSyntax;
+
+    /// Configures how this backend structures `SELECT` queries
+    ///
+    /// This allows backends to provide custom [`QueryFragment`](crate::query_builder::QueryFragment)
+    /// implementations for [`Alias<T>`](crate::query_source::Alias)
+    ///
+    #[cfg_attr(
+        feature = "i-implement-a-third-party-backend-and-opt-into-breaking-changes",
+        doc = "See [`sql_dialect::alias_syntax`] for provided default implementations"
+    )]
+    type AliasSyntax;
 }
 
 /// This module contains all options provided by diesel to configure the [`SqlDialect`] trait.
@@ -516,6 +527,18 @@ pub(crate) mod sql_dialect {
         #[derive(Debug, Copy, Clone)]
         pub struct AnsiSqlSelectStatement;
     }
+
+    /// This module contains all reusable options to configure
+    /// [`SqlDialect::AliasSyntax`]
+    #[diesel_derives::__diesel_public_if(
+        feature = "i-implement-a-third-party-backend-and-opt-into-breaking-changes"
+    )]
+    pub mod alias_syntax {
+        /// Indicates that this backend uses `table AS alias` for
+        /// defining table aliases
+        #[derive(Debug, Copy, Clone)]
+        pub struct AsAliasSyntax;
+    }
 }
 
 // These traits are not part of the public API

diff --git a/diesel/src/mysql/backend.rs b/diesel/src/mysql/backend.rs
@@ -88,6 +88,7 @@ impl SqlDialect for Mysql {
     type ArrayComparison = sql_dialect::array_comparison::AnsiSqlArrayComparison;
 
     type ConcatClause = MysqlConcatClause;
+    type AliasSyntax = sql_dialect::alias_syntax::AsAliasSyntax;
 }
 
 impl DieselReserveSpecialization for Mysql {}

diff --git a/diesel/src/pg/backend.rs b/diesel/src/pg/backend.rs
@@ -139,6 +139,7 @@ impl SqlDialect for Pg {
 
     type ExistsSyntax = sql_dialect::exists_syntax::AnsiSqlExistsSyntax;
     type ArrayComparison = PgStyleArrayComparison;
+    type AliasSyntax = sql_dialect::alias_syntax::AsAliasSyntax;
 }
 
 impl DieselReserveSpecialization for Pg {}

diff --git a/diesel/src/query_source/aliasing/alias.rs b/diesel/src/query_source/aliasing/alias.rs
@@ -1,7 +1,7 @@
 use super::field_alias_mapper::FieldAliasMapper;
 use super::{AliasSource, AliasedField};
 
-use crate::backend::Backend;
+use crate::backend::{sql_dialect, Backend};
 use crate::expression::{Expression, SelectableExpression, ValidGrouping};
 use crate::helper_types::AliasedFields;
 use crate::query_builder::{AsQuery, AstPass, FromClause, QueryFragment, QueryId, SelectStatement};
@@ -14,7 +14,12 @@ use std::marker::PhantomData;
 /// Represents an alias within diesel's query builder
 ///
 /// See [`alias!`](crate::alias) for more details.
+#[diesel_derives::__diesel_public_if(
+    feature = "i-implement-a-third-party-backend-and-opt-into-breaking-changes",
+    public_fields(source)
+)]
 pub struct Alias<S> {
+    /// The inner alias definition
     pub(crate) source: S,
 }
 
@@ -80,6 +85,17 @@ where
 }
 
 impl<S, DB> QueryFragment<DB> for Alias<S>
+where
+    S: AliasSource,
+    DB: Backend,
+    Self: QueryFragment<DB, DB::AliasSyntax>,
+{
+    fn walk_ast<'b>(&'b self, pass: AstPass<'_, 'b, DB>) -> QueryResult<()> {
+        <Self as QueryFragment<DB, DB::AliasSyntax>>::walk_ast(self, pass)
+    }
+}
+
+impl<S, DB> QueryFragment<DB, sql_dialect::alias_syntax::AsAliasSyntax> for Alias<S>
 where
     S: AliasSource,
     DB: Backend,

diff --git a/diesel/src/sqlite/backend.rs b/diesel/src/sqlite/backend.rs
@@ -66,6 +66,7 @@ impl SqlDialect for Sqlite {
 
     type ExistsSyntax = sql_dialect::exists_syntax::AnsiSqlExistsSyntax;
     type ArrayComparison = sql_dialect::array_comparison::AnsiSqlArrayComparison;
+    type AliasSyntax = sql_dialect::alias_syntax::AsAliasSyntax;
 }
 
 impl DieselReserveSpecialization for Sqlite {}

diff --git a/diesel_derives/src/multiconnection.rs b/diesel_derives/src/multiconnection.rs
@@ -1035,6 +1035,10 @@ fn generate_querybuilder(connection_types: &[ConnectionVariant]) -> TokenStream
         quote::quote! {
             <Tab, V, QId, const HAS_STATIC_QUERY_ID: bool> diesel::query_builder::QueryFragment<super::backend::MultiBackend, super::backend::MultiBatchInsertSupport>
                 for diesel::internal::derives::multiconnection::BatchInsert<V, Tab, QId, HAS_STATIC_QUERY_ID>
+        },
+        quote::quote! {
+            <S> diesel::query_builder::QueryFragment<super::backend::MultiBackend, super::backend::MultiAliasSyntax>
+                for diesel::query_source::Alias<S>
         }
     ])
     .map(|t| generate_queryfragment_impls(t, &query_fragment_bounds));
@@ -1414,6 +1418,7 @@ fn generate_backend(connection_types: &[ConnectionVariant]) -> TokenStream {
         pub struct MultiArrayComparisonSyntax;
         pub struct MultiConcatClauseSyntax;
         pub struct MultiSelectStatementSyntax;
+        pub struct MultiAliasSyntax;
 
         impl diesel::backend::SqlDialect for MultiBackend {
             type ReturningClause = MultiReturningClause;
@@ -1427,6 +1432,7 @@ fn generate_backend(connection_types: &[ConnectionVariant]) -> TokenStream {
             type ArrayComparison = MultiArrayComparisonSyntax;
             type ConcatClause = MultiConcatClauseSyntax;
             type SelectStatementSyntax = MultiSelectStatementSyntax;
+            type AliasSyntax = MultiAliasSyntax;
         }
 
         impl diesel::internal::derives::multiconnection::TrustedBackend for MultiBackend {}