Translate COALESCE as ISNULL (#34171)

Author: ranma42

src/EFCore.SqlServer/Query/Internal/SqlServerQuerySqlGenerator.cs

@@ -202,6 +202,53 @@ protected override Expression VisitValues(ValuesExpression valuesExpression)
         return valuesExpression;
     }
 
+    /// <summary>
+    ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
+    ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
+    ///     any release. You should only use it directly in your code with extreme caution and knowing that
+    ///     doing so can result in application failures when updating to a new Entity Framework Core release.
+    /// </summary>
+    protected override Expression VisitSqlFunction(SqlFunctionExpression sqlFunctionExpression)
+    {
+        if (sqlFunctionExpression is { IsBuiltIn: true, Arguments: not null }
+            && string.Equals(sqlFunctionExpression.Name, "COALESCE", StringComparison.OrdinalIgnoreCase))
+        {
+            var type = sqlFunctionExpression.Type;
+            var typeMapping = sqlFunctionExpression.TypeMapping;
+            var defaultTypeMapping = _typeMappingSource.FindMapping(type);
+
+            // ISNULL always return a value having the same type as its first
+            // argument. Ideally we would convert the argument to have the
+            // desired type and type mapping, but currently EFCore has some
+            // trouble in computing types of non-homogeneous expressions
+            // (tracked in https://github.com/dotnet/efcore/issues/15586). To
+            // stay on the safe side we only use ISNULL if:
+            //  - all sub-expressions have the same type as the expression
+            //  - all sub-expressions have the same type mapping as the expression
+            //  - the expression is using the default type mapping (combined
+            //    with the two above, this implies that all of the expressions
+            //    are using the default type mapping of the type)
+            if (defaultTypeMapping == typeMapping
+                && sqlFunctionExpression.Arguments.All(a => a.Type == type && a.TypeMapping == typeMapping)) {
+
+                var head = sqlFunctionExpression.Arguments[0];
+                sqlFunctionExpression = (SqlFunctionExpression)sqlFunctionExpression
+                    .Arguments
+                    .Skip(1)
+                    .Aggregate(head, (l, r) => new SqlFunctionExpression(
+                        "ISNULL",
+                        arguments: [l, r],
+                        nullable: true,
+                        argumentsPropagateNullability: [false, false],
+                        sqlFunctionExpression.Type,
+                        sqlFunctionExpression.TypeMapping
+                    ));
+            }
+        }
+
+        return base.VisitSqlFunction(sqlFunctionExpression);
+    }
+
     /// <summary>
     ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
     ///     the same compatibility standards as public APIs. It may be changed or removed without notice in

test/EFCore.Cosmos.FunctionalTests/Query/NorthwindMiscellaneousQueryCosmosTest.cs

@@ -3229,6 +3229,49 @@ public override async Task Entity_equality_orderby_descending_subquery_composite
         AssertSql();
     }
 
+    public override Task Coalesce_Correct_Multiple_Same_TypeMapping(bool async)
+        => Fixture.NoSyncTest(
+            async, async a =>
+            {
+                await base.Coalesce_Correct_Multiple_Same_TypeMapping(async);
+
+                AssertSql(
+                    """
+SELECT VALUE
+{
+    "ReportsTo" : c["ReportsTo"],
+    "c" : 1,
+    "c0" : 2,
+    "c1" : 3
+}
+FROM root c
+ORDER BY c["EmployeeID"]
+""");
+            });
+
+    public override Task Coalesce_Correct_TypeMapping_Double(bool async)
+        => Fixture.NoSyncTest(
+            async, async a =>
+            {
+                await base.Coalesce_Correct_TypeMapping_Double(async);
+
+                AssertSql();
+            });
+
+    public override Task Coalesce_Correct_TypeMapping_String(bool async)
+        => Fixture.NoSyncTest(
+            async, async a =>
+            {
+                await base.Coalesce_Correct_TypeMapping_String(async);
+
+                AssertSql(
+                    """
+SELECT VALUE ((c["Region"] != null) ? c["Region"] : "no region specified")
+FROM root c
+ORDER BY c["id"]
+""");
+            });
+
     public override async Task Null_Coalesce_Short_Circuit(bool async)
     {
         // Cosmos client evaluation. Issue #17246.
@@ -3347,7 +3390,7 @@ public override async Task SelectMany_primitive_select_subquery(bool async)
         // Cosmos client evaluation. Issue #17246.
         Assert.Equal(
             CoreStrings.ExpressionParameterizationExceptionSensitive(
-                "value(Microsoft.EntityFrameworkCore.Query.NorthwindMiscellaneousQueryTestBase`1+<>c__DisplayClass172_0[Microsoft.EntityFrameworkCore.Query.NorthwindQueryCosmosFixture`1[Microsoft.EntityFrameworkCore.TestUtilities.NoopModelCustomizer]]).ss.Set().Any()"),
+                "value(Microsoft.EntityFrameworkCore.Query.NorthwindMiscellaneousQueryTestBase`1+<>c__DisplayClass175_0[Microsoft.EntityFrameworkCore.Query.NorthwindQueryCosmosFixture`1[Microsoft.EntityFrameworkCore.TestUtilities.NoopModelCustomizer]]).ss.Set().Any()"),
             (await Assert.ThrowsAsync<InvalidOperationException>(
                 () => base.SelectMany_primitive_select_subquery(async))).Message);
 

test/EFCore.Specification.Tests/Query/NorthwindMiscellaneousQueryTestBase.cs

@@ -723,6 +723,31 @@ public virtual Task Ternary_should_not_evaluate_both_sides_with_parameter(bool a
                 }));
     }
 
+    [ConditionalTheory]
+    [MemberData(nameof(IsAsyncData))]
+    public virtual Task Coalesce_Correct_Multiple_Same_TypeMapping(bool async)
+        => AssertQuery(
+            async,
+            ss => ss.Set<Employee>().OrderBy(e => e.EmployeeID)
+                .Select(e => (e.ReportsTo + 1L) ?? (e.ReportsTo + 2L) ?? (e.ReportsTo + 3L)),
+            assertOrder: true);
+
+    [ConditionalTheory(Skip = "issue #15586")]
+    [MemberData(nameof(IsAsyncData))]
+    public virtual Task Coalesce_Correct_TypeMapping_Double(bool async)
+        => AssertQuery(
+            async,
+            ss => ss.Set<Employee>().OrderBy(e => e.EmployeeID).Select(e => e.ReportsTo ?? 2.25),
+            assertOrder: true);
+
+    [ConditionalTheory]
+    [MemberData(nameof(IsAsyncData))]
+    public virtual Task Coalesce_Correct_TypeMapping_String(bool async)
+        => AssertQuery(
+            async,
+            ss => ss.Set<Customer>().OrderBy(c => c.CustomerID).Select(c => c.Region ?? "no region specified"),
+            assertOrder: true);
+
     [ConditionalTheory]
     [MemberData(nameof(IsAsyncData))]
     public virtual Task Null_Coalesce_Short_Circuit(bool async)

test/EFCore.SqlServer.FunctionalTests/Query/ComplexNavigationsQuerySqlServer160Test.cs

@@ -3980,7 +3980,7 @@ public override async Task Nested_object_constructed_from_group_key_properties(b
 
         AssertSql(
             """
-SELECT [l].[Id], [l].[Name], [l].[Date], [l0].[Id], [l1].[Name], [l0].[Date], [l0].[Level1_Optional_Id], [l0].[Level1_Required_Id], COALESCE(SUM(CAST(LEN([l].[Name]) AS int)), 0) AS [Aggregate]
+SELECT [l].[Id], [l].[Name], [l].[Date], [l0].[Id], [l1].[Name], [l0].[Date], [l0].[Level1_Optional_Id], [l0].[Level1_Required_Id], ISNULL(SUM(CAST(LEN([l].[Name]) AS int)), 0) AS [Aggregate]
 FROM [LevelOne] AS [l]
 LEFT JOIN [LevelTwo] AS [l0] ON [l].[Id] = [l0].[Level1_Optional_Id]
 LEFT JOIN [LevelTwo] AS [l1] ON [l].[Id] = [l1].[Level1_Required_Id]

test/EFCore.SqlServer.FunctionalTests/Query/ComplexNavigationsQuerySqlServerTest.cs

@@ -3980,7 +3980,7 @@ public override async Task Nested_object_constructed_from_group_key_properties(b
 
         AssertSql(
             """
-SELECT [l].[Id], [l].[Name], [l].[Date], [l0].[Id], [l1].[Name], [l0].[Date], [l0].[Level1_Optional_Id], [l0].[Level1_Required_Id], COALESCE(SUM(CAST(LEN([l].[Name]) AS int)), 0) AS [Aggregate]
+SELECT [l].[Id], [l].[Name], [l].[Date], [l0].[Id], [l1].[Name], [l0].[Date], [l0].[Level1_Optional_Id], [l0].[Level1_Required_Id], ISNULL(SUM(CAST(LEN([l].[Name]) AS int)), 0) AS [Aggregate]
 FROM [LevelOne] AS [l]
 LEFT JOIN [LevelTwo] AS [l0] ON [l].[Id] = [l0].[Level1_Optional_Id]
 LEFT JOIN [LevelTwo] AS [l1] ON [l].[Id] = [l1].[Level1_Required_Id]

test/EFCore.SqlServer.FunctionalTests/Query/ComplexNavigationsSharedTypeQuerySqlServer160Test.cs

@@ -781,7 +781,7 @@ public override async Task Nested_object_constructed_from_group_key_properties(b
 
         AssertSql(
             """
-SELECT [s].[Id], [s].[Name], [s].[Date], [s].[InnerId] AS [Id], [s].[Level2_Name0] AS [Name], [s].[OneToOne_Required_PK_Date] AS [Date], [s].[Level1_Optional_Id], [s].[Level1_Required_Id], COALESCE(SUM(CAST(LEN([s].[Name]) AS int)), 0) AS [Aggregate]
+SELECT [s].[Id], [s].[Name], [s].[Date], [s].[InnerId] AS [Id], [s].[Level2_Name0] AS [Name], [s].[OneToOne_Required_PK_Date] AS [Date], [s].[Level1_Optional_Id], [s].[Level1_Required_Id], ISNULL(SUM(CAST(LEN([s].[Name]) AS int)), 0) AS [Aggregate]
 FROM (
     SELECT [l].[Id], [l].[Date], [l].[Name], [l1].[OneToOne_Required_PK_Date], [l1].[Level1_Optional_Id], [l1].[Level1_Required_Id], [l3].[Level2_Name] AS [Level2_Name0], CASE
         WHEN [l1].[OneToOne_Required_PK_Date] IS NOT NULL AND [l1].[Level1_Required_Id] IS NOT NULL AND [l1].[OneToMany_Required_Inverse2Id] IS NOT NULL THEN [l1].[Id]

test/EFCore.SqlServer.FunctionalTests/Query/ComplexNavigationsSharedTypeQuerySqlServerTest.cs

@@ -783,7 +783,7 @@ public override async Task Nested_object_constructed_from_group_key_properties(b
 
         AssertSql(
             """
-SELECT [s].[Id], [s].[Name], [s].[Date], [s].[InnerId] AS [Id], [s].[Level2_Name0] AS [Name], [s].[OneToOne_Required_PK_Date] AS [Date], [s].[Level1_Optional_Id], [s].[Level1_Required_Id], COALESCE(SUM(CAST(LEN([s].[Name]) AS int)), 0) AS [Aggregate]
+SELECT [s].[Id], [s].[Name], [s].[Date], [s].[InnerId] AS [Id], [s].[Level2_Name0] AS [Name], [s].[OneToOne_Required_PK_Date] AS [Date], [s].[Level1_Optional_Id], [s].[Level1_Required_Id], ISNULL(SUM(CAST(LEN([s].[Name]) AS int)), 0) AS [Aggregate]
 FROM (
     SELECT [l].[Id], [l].[Date], [l].[Name], [l1].[OneToOne_Required_PK_Date], [l1].[Level1_Optional_Id], [l1].[Level1_Required_Id], [l3].[Level2_Name] AS [Level2_Name0], CASE
         WHEN [l1].[OneToOne_Required_PK_Date] IS NOT NULL AND [l1].[Level1_Required_Id] IS NOT NULL AND [l1].[OneToMany_Required_Inverse2Id] IS NOT NULL THEN [l1].[Id]

test/EFCore.SqlServer.FunctionalTests/Query/GearsOfWarQuerySqlServerTest.cs

@@ -3475,7 +3475,7 @@ public override async Task ToString_nullable_enum_property_projection(bool async
 SELECT CASE [w].[AmmunitionType]
     WHEN 1 THEN N'Cartridge'
     WHEN 2 THEN N'Shell'
-    ELSE COALESCE(CAST([w].[AmmunitionType] AS nvarchar(max)), N'')
+    ELSE ISNULL(CAST([w].[AmmunitionType] AS nvarchar(max)), N'')
 END
 FROM [Weapons] AS [w]
 """);
@@ -3504,7 +3504,7 @@ FROM [Weapons] AS [w]
 WHERE CASE [w].[AmmunitionType]
     WHEN 1 THEN N'Cartridge'
     WHEN 2 THEN N'Shell'
-    ELSE COALESCE(CAST([w].[AmmunitionType] AS nvarchar(max)), N'')
+    ELSE ISNULL(CAST([w].[AmmunitionType] AS nvarchar(max)), N'')
 END LIKE N'%Cart%'
 """);
     }
@@ -4883,7 +4883,7 @@ public override async Task Select_subquery_projecting_single_constant_int(bool a
 
         AssertSql(
             """
-SELECT [s].[Name], COALESCE((
+SELECT [s].[Name], ISNULL((
     SELECT TOP(1) 42
     FROM [Gears] AS [g]
     WHERE [s].[Id] = [g].[SquadId] AND [g].[HasSoulPatch] = CAST(1 AS bit)), 0) AS [Gear]
@@ -4911,7 +4911,7 @@ public override async Task Select_subquery_projecting_single_constant_bool(bool
 
         AssertSql(
             """
-SELECT [s].[Name], COALESCE((
+SELECT [s].[Name], ISNULL((
     SELECT TOP(1) CAST(1 AS bit)
     FROM [Gears] AS [g]
     WHERE [s].[Id] = [g].[SquadId] AND [g].[HasSoulPatch] = CAST(1 AS bit)), CAST(0 AS bit)) AS [Gear]
@@ -5546,7 +5546,7 @@ public override async Task String_concat_on_various_types(bool async)
 
         AssertSql(
             """
-SELECT N'HasSoulPatch ' + CAST([g].[HasSoulPatch] AS nvarchar(max)) + N' HasSoulPatch' AS [HasSoulPatch], N'Rank ' + CAST([g].[Rank] AS nvarchar(max)) + N' Rank' AS [Rank], N'SquadId ' + CAST([g].[SquadId] AS nvarchar(max)) + N' SquadId' AS [SquadId], N'Rating ' + COALESCE(CAST([m].[Rating] AS nvarchar(max)), N'') + N' Rating' AS [Rating], N'Timeline ' + CAST([m].[Timeline] AS nvarchar(max)) + N' Timeline' AS [Timeline]
+SELECT N'HasSoulPatch ' + CAST([g].[HasSoulPatch] AS nvarchar(max)) + N' HasSoulPatch' AS [HasSoulPatch], N'Rank ' + CAST([g].[Rank] AS nvarchar(max)) + N' Rank' AS [Rank], N'SquadId ' + CAST([g].[SquadId] AS nvarchar(max)) + N' SquadId' AS [SquadId], N'Rating ' + ISNULL(CAST([m].[Rating] AS nvarchar(max)), N'') + N' Rating' AS [Rating], N'Timeline ' + CAST([m].[Timeline] AS nvarchar(max)) + N' Timeline' AS [Timeline]
 FROM [Gears] AS [g]
 CROSS JOIN [Missions] AS [m]
 ORDER BY [g].[Nickname], [m].[Id]
@@ -6616,7 +6616,7 @@ public override async Task Complex_GroupBy_after_set_operator(bool async)
 
         AssertSql(
             """
-SELECT [u].[Name], [u].[Count], COALESCE(SUM([u].[Count]), 0) AS [Sum]
+SELECT [u].[Name], [u].[Count], ISNULL(SUM([u].[Count]), 0) AS [Sum]
 FROM (
     SELECT [c].[Name], (
         SELECT COUNT(*)
@@ -6642,7 +6642,7 @@ public override async Task Complex_GroupBy_after_set_operator_using_result_selec
 
         AssertSql(
             """
-SELECT [u].[Name], [u].[Count], COALESCE(SUM([u].[Count]), 0) AS [Sum]
+SELECT [u].[Name], [u].[Count], ISNULL(SUM([u].[Count]), 0) AS [Sum]
 FROM (
     SELECT [c].[Name], (
         SELECT COUNT(*)
@@ -9076,7 +9076,7 @@ public override async Task Set_operator_with_navigation_in_projection_groupby_ag
         AssertSql(
             """
 SELECT [s].[Name], (
-    SELECT COALESCE(SUM(CAST(LEN([c].[Location]) AS int)), 0)
+    SELECT ISNULL(SUM(CAST(LEN([c].[Location]) AS int)), 0)
     FROM [Gears] AS [g2]
     INNER JOIN [Squads] AS [s0] ON [g2].[SquadId] = [s0].[Id]
     INNER JOIN [Cities] AS [c] ON [g2].[CityOfBirthName] = [c].[Name]
@@ -9160,7 +9160,7 @@ LEFT JOIN (
         SELECT [w].[Id], [w].[AmmunitionType], [w].[IsAutomatic], [w].[Name], [w].[OwnerFullName], [w].[SynergyWithId], ROW_NUMBER() OVER(PARTITION BY [w].[OwnerFullName] ORDER BY [w].[Id]) AS [row]
         FROM [Weapons] AS [w]
     ) AS [w0]
-    WHERE [w0].[row] <= COALESCE((
+    WHERE [w0].[row] <= ISNULL((
         SELECT [n].[value]
         FROM OPENJSON(@numbers) WITH ([value] int '$') AS [n]
         ORDER BY [n].[value]

test/EFCore.SqlServer.FunctionalTests/Query/NorthwindAggregateOperatorsQuerySqlServerTest.cs

@@ -815,7 +815,7 @@ public override async Task Sum_over_uncorrelated_subquery(bool async)
         // #34256: rewrite query to avoid "Cannot perform an aggregate function on an expression containing an aggregate or a subquery"
         AssertSql(
             """
-SELECT COALESCE(SUM([s].[value]), 0)
+SELECT ISNULL(SUM([s].[value]), 0)
 FROM [Customers] AS [c]
 CROSS JOIN (
     SELECT COUNT(*) AS [value]
@@ -2721,7 +2721,7 @@ public override async Task Project_constant_Sum(bool async)
 
         AssertSql(
             """
-SELECT COALESCE(SUM(1), 0)
+SELECT ISNULL(SUM(1), 0)
 FROM [Employees] AS [e]
 """);
     }
@@ -3081,7 +3081,7 @@ public override async Task Contains_inside_Sum_without_GroupBy(bool async)
             """
 @cities='["London","Berlin"]' (Size = 4000)
 
-SELECT COALESCE(SUM([s].[value]), 0)
+SELECT ISNULL(SUM([s].[value]), 0)
 FROM [Customers] AS [c]
 OUTER APPLY (
     SELECT CASE

test/EFCore.SqlServer.FunctionalTests/Query/NorthwindGroupByQuerySqlServerTest.cs

@@ -272,7 +272,7 @@ public override async Task GroupBy_aggregate_projecting_conditional_expression(b
             """
 SELECT [o].[OrderDate] AS [Key], CASE
     WHEN COUNT(*) = 0 THEN 1
-    ELSE COALESCE(SUM(CASE
+    ELSE ISNULL(SUM(CASE
         WHEN [o].[OrderID] % 2 = 0 THEN 1
         ELSE 0
     END), 0) / COUNT(*)
@@ -1939,7 +1939,7 @@ public override async Task GroupBy_Sum_constant(bool async)
 
         AssertSql(
             """
-SELECT COALESCE(SUM(1), 0)
+SELECT ISNULL(SUM(1), 0)
 FROM [Orders] AS [o]
 GROUP BY [o].[CustomerID]
 """);
@@ -2699,7 +2699,7 @@ public override async Task GroupBy_aggregate_followed_by_another_GroupBy_aggrega
 
         AssertSql(
             """
-SELECT [o1].[Key0] AS [Key], COALESCE(SUM([o1].[Count]), 0) AS [Count]
+SELECT [o1].[Key0] AS [Key], ISNULL(SUM([o1].[Count]), 0) AS [Count]
 FROM (
     SELECT [o0].[Count], 1 AS [Key0]
     FROM (

test/EFCore.SqlServer.FunctionalTests/Query/NorthwindJoinQuerySqlServerTest.cs

@@ -596,9 +596,9 @@ public override async Task GroupJoin_aggregate_anonymous_key_selectors(bool asyn
         await base.GroupJoin_aggregate_anonymous_key_selectors(async);
 
         AssertSql(
-"""
+            """
 SELECT [c].[CustomerID], (
-    SELECT COALESCE(SUM(CAST(LEN([o].[CustomerID]) AS int)), 0)
+    SELECT ISNULL(SUM(CAST(LEN([o].[CustomerID]) AS int)), 0)
     FROM [Orders] AS [o]
     WHERE [c].[City] IS NOT NULL AND [c].[CustomerID] = [o].[CustomerID] AND [c].[City] = N'London') AS [Sum]
 FROM [Customers] AS [c]
@@ -610,9 +610,9 @@ public override async Task GroupJoin_aggregate_anonymous_key_selectors2(bool asy
         await base.GroupJoin_aggregate_anonymous_key_selectors2(async);
 
         AssertSql(
-"""
+            """
 SELECT [c].[CustomerID], (
-    SELECT COALESCE(SUM(CAST(LEN([o].[CustomerID]) AS int)), 0)
+    SELECT ISNULL(SUM(CAST(LEN([o].[CustomerID]) AS int)), 0)
     FROM [Orders] AS [o]
     WHERE [c].[CustomerID] = [o].[CustomerID] AND 1996 = DATEPART(year, [o].[OrderDate])) AS [Sum]
 FROM [Customers] AS [c]
@@ -624,9 +624,9 @@ public override async Task GroupJoin_aggregate_anonymous_key_selectors_one_argum
         await base.GroupJoin_aggregate_anonymous_key_selectors_one_argument(async);
 
         AssertSql(
-"""
+            """
 SELECT [c].[CustomerID], (
-    SELECT COALESCE(SUM(CAST(LEN([o].[CustomerID]) AS int)), 0)
+    SELECT ISNULL(SUM(CAST(LEN([o].[CustomerID]) AS int)), 0)
     FROM [Orders] AS [o]
     WHERE [c].[CustomerID] = [o].[CustomerID]) AS [Sum]
 FROM [Customers] AS [c]

test/EFCore.SqlServer.FunctionalTests/Query/NorthwindKeylessEntitiesQuerySqlServerTest.cs

@@ -148,7 +148,7 @@ public override async Task KeylessEntity_groupby(bool async)
 
         AssertSql(
             """
-SELECT [m].[City] AS [Key], COUNT(*) AS [Count], COALESCE(SUM(CAST(LEN([m].[Address]) AS int)), 0) AS [Sum]
+SELECT [m].[City] AS [Key], COUNT(*) AS [Count], ISNULL(SUM(CAST(LEN([m].[Address]) AS int)), 0) AS [Sum]
 FROM (
     SELECT [c].[CustomerID], [c].[Address], [c].[City], [c].[CompanyName], [c].[ContactName], [c].[ContactTitle], [c].[Country], [c].[Fax], [c].[Phone], [c].[PostalCode], [c].[Region] FROM [Customers] AS [c]
 ) AS [m]