Fix missing type mapping for CONVERT

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

@@ -102,12 +102,13 @@ public SqlServerObjectToStringTranslator(ISqlExpressionFactory sqlExpressionFact
         }
 
         return TypeMapping.TryGetValue(instance.Type, out var storeType)
-            ? _sqlExpressionFactory.Function(
-                "CONVERT",
-                new[] { _sqlExpressionFactory.Fragment(storeType), instance },
-                nullable: true,
-                argumentsPropagateNullability: new[] { false, true },
-                typeof(string))
+            ? _sqlExpressionFactory.ApplyDefaultTypeMapping(
+                _sqlExpressionFactory.Function(
+                    "CONVERT",
+                    new[] { _sqlExpressionFactory.Fragment(storeType), instance },
+                    nullable: true,
+                    argumentsPropagateNullability: new[] { false, true },
+                    typeof(string)))
             : null;
     }
 }

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

@@ -1711,6 +1711,30 @@ FROM root c
 """);
     }
 
+    public override async Task Select_ToString_IndexOf(bool async)
+    {
+        await base.Select_ToString_IndexOf(async);
+
+        AssertSql(
+            """
+SELECT c["OrderID"]
+FROM root c
+WHERE (c["Discriminator"] = "Order")
+""");
+    }
+
+    public override async Task Select_IndexOf_ToString(bool async)
+    {
+        await base.Select_IndexOf_ToString(async);
+
+        AssertSql(
+            """
+SELECT c["OrderID"]
+FROM root c
+WHERE (c["Discriminator"] = "Order")
+""");
+    }
+
     public override Task String_Join_over_non_nullable_column(bool async)
         => AssertTranslationFailed(() => base.String_Join_over_non_nullable_column(async));
 

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

@@ -1852,4 +1852,18 @@ public virtual Task Where_DateOnly_FromDateTime(bool async)
             ss => ss.Set<Order>()
                 .Where(o => o.OrderDate.HasValue && DateOnly.FromDateTime(o.OrderDate.Value) == new DateOnly(1996, 9, 16))
                 .AsTracking());
+
+    [ConditionalTheory]
+    [MemberData(nameof(IsAsyncData))]
+    public virtual Task Select_ToString_IndexOf(bool async)
+        => AssertQuery(
+            async,
+            ss => ss.Set<Order>().Select(x => x.OrderID.ToString().IndexOf("123")));
+
+    [ConditionalTheory]
+    [MemberData(nameof(IsAsyncData))]
+    public virtual Task Select_IndexOf_ToString(bool async)
+        => AssertQuery(
+            async,
+            ss => ss.Set<Order>().Select(x => "123".IndexOf(x.OrderID.ToString())));
 }

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

@@ -2723,6 +2723,31 @@ public override Task Regex_IsMatch_MethodCall_constant_input(bool async)
     public override Task Datetime_subtraction_TotalDays(bool async)
         => AssertTranslationFailed(() => base.Datetime_subtraction_TotalDays(async));
 
+    public override async Task Select_ToString_IndexOf(bool async)
+    {
+        await base.Select_ToString_IndexOf(async);
+
+        AssertSql(
+            """
+SELECT CAST(CHARINDEX(N'123', CONVERT(varchar(11), [o].[OrderID])) AS int) - 1
+FROM [Orders] AS [o]
+""");
+    }
+
+    public override async Task Select_IndexOf_ToString(bool async)
+    {
+        await base.Select_IndexOf_ToString(async);
+
+        AssertSql(
+            """
+SELECT CASE
+    WHEN CONVERT(varchar(11), [o].[OrderID]) = N'' THEN 0
+    ELSE CAST(CHARINDEX(CONVERT(varchar(11), [o].[OrderID]), N'123') AS int) - 1
+END
+FROM [Orders] AS [o]
+""");
+    }
+
     [ConditionalTheory]
     [MemberData(nameof(IsAsyncData))]
     public virtual async Task StandardDeviation(bool async)

test/EFCore.Sqlite.FunctionalTests/Query/NorthwindFunctionsQuerySqliteTest.cs

@@ -1480,6 +1480,28 @@ public override async Task Where_DateOnly_FromDateTime(bool async)
 """);
     }
 
+    public override async Task Select_ToString_IndexOf(bool async)
+    {
+        await base.Select_ToString_IndexOf(async);
+
+        AssertSql(
+            """
+SELECT instr(CAST("o"."OrderID" AS TEXT), '123') - 1
+FROM "Orders" AS "o"
+""");
+    }
+
+    public override async Task Select_IndexOf_ToString(bool async)
+    {
+        await base.Select_IndexOf_ToString(async);
+
+        AssertSql(
+            """
+SELECT instr('123', CAST("o"."OrderID" AS TEXT)) - 1
+FROM "Orders" AS "o"
+""");
+    }
+
     private void AssertSql(params string[] expected)
         => Fixture.TestSqlLoggerFactory.AssertBaseline(expected);
 }