Fix Nullable<T>.ToString()

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

@@ -108,13 +108,15 @@ public SqlServerObjectToStringTranslator(ISqlExpressionFactory sqlExpressionFact
         // Enums are handled by EnumMethodTranslator
 
         return TypeMapping.TryGetValue(instance.Type, out var storeType)
-            ? _sqlExpressionFactory.Function(
-                "CONVERT",
-                new[] { _sqlExpressionFactory.Fragment(storeType), instance },
-                nullable: true,
-                argumentsPropagateNullability: new[] { false, true },
-                typeof(string),
-                _typeMappingSource.GetMapping(storeType))
+            ? _sqlExpressionFactory.Coalesce(
+                _sqlExpressionFactory.Function(
+                    "CONVERT",
+                    new[] { _sqlExpressionFactory.Fragment(storeType), instance },
+                    nullable: true,
+                    argumentsPropagateNullability: new[] { false, true },
+                    typeof(string),
+                    _typeMappingSource.GetMapping(storeType)),
+                _sqlExpressionFactory.Constant(string.Empty))
             : null;
     }
 }

src/EFCore.Sqlite.Core/Query/Internal/Translators/SqliteObjectToStringTranslator.cs

@@ -103,7 +103,9 @@ public SqliteObjectToStringTranslator(ISqlExpressionFactory sqlExpressionFactory
         // Enums are handled by EnumMethodTranslator
 
         return TypeMapping.Contains(instance.Type)
-            ? _sqlExpressionFactory.Convert(instance, typeof(string))
+            ? _sqlExpressionFactory.Coalesce(
+                _sqlExpressionFactory.Convert(instance, typeof(string)),
+                _sqlExpressionFactory.Constant(string.Empty))
             : null;
     }
 }

test/EFCore.Relational.Specification.Tests/BulkUpdates/NorthwindBulkUpdatesTestBase.cs

@@ -1019,18 +1019,7 @@ public virtual Task Update_Where_Join_set_property_from_joined_single_result_tab
             e => e.c,
             s => s.SetProperty(c => c.c.City, c => c.LastOrder.OrderDate.Value.Year.ToString()),
             rowsAffectedCount: 8,
-            (b, a) => Assert.All(
-                a, c =>
-                {
-                    if (c.CustomerID == "FISSA")
-                    {
-                        Assert.Null(c.City);
-                    }
-                    else
-                    {
-                        Assert.NotNull(c.City);
-                    }
-                }));
+            (b, a) => Assert.All(a, c => Assert.NotNull(c.City)));
 
     [ConditionalTheory]
     [MemberData(nameof(IsAsyncData))]
@@ -1055,18 +1044,7 @@ public virtual Task Update_Where_Join_set_property_from_joined_single_result_sca
             e => e.c,
             s => s.SetProperty(c => c.c.City, c => c.LastOrderDate.ToString()),
             rowsAffectedCount: 8,
-            (b, a) => Assert.All(
-                a, c =>
-                {
-                    if (c.CustomerID == "FISSA")
-                    {
-                        Assert.Null(c.City);
-                    }
-                    else
-                    {
-                        Assert.NotNull(c.City);
-                    }
-                }));
+            (b, a) => Assert.All(a, c => Assert.NotNull(c.City)));
 
     [ConditionalTheory]
     [MemberData(nameof(IsAsyncData))]

test/EFCore.SqlServer.FunctionalTests/BulkUpdates/NonSharedModelBulkUpdatesSqlServerTest.cs

@@ -120,7 +120,7 @@ public override async Task Update_owned_and_non_owned_properties_with_table_shar
             """
 UPDATE [o]
 SET [o].[OwnedReference_Number] = CAST(LEN([o].[Title]) AS int),
-    [o].[Title] = CONVERT(varchar(11), [o].[OwnedReference_Number])
+    [o].[Title] = COALESCE(CONVERT(varchar(11), [o].[OwnedReference_Number]), '')
 FROM [Owner] AS [o]
 """);
     }

test/EFCore.SqlServer.FunctionalTests/BulkUpdates/NorthwindBulkUpdatesSqlServerTest.cs

@@ -1414,11 +1414,11 @@ public override async Task Update_Where_Join_set_property_from_joined_single_res
         AssertExecuteUpdateSql(
             """
 UPDATE [c]
-SET [c].[City] = CONVERT(varchar(11), DATEPART(year, (
+SET [c].[City] = COALESCE(CONVERT(varchar(11), DATEPART(year, (
     SELECT TOP(1) [o].[OrderDate]
     FROM [Orders] AS [o]
     WHERE [c].[CustomerID] = [o].[CustomerID]
-    ORDER BY [o].[OrderDate] DESC)))
+    ORDER BY [o].[OrderDate] DESC))), '')
 FROM [Customers] AS [c]
 WHERE [c].[CustomerID] LIKE N'F%'
 """);
@@ -1449,11 +1449,11 @@ public override async Task Update_Where_Join_set_property_from_joined_single_res
         AssertExecuteUpdateSql(
             """
 UPDATE [c]
-SET [c].[City] = CONVERT(varchar(11), DATEPART(year, (
+SET [c].[City] = COALESCE(CONVERT(varchar(11), DATEPART(year, (
     SELECT TOP(1) [o].[OrderDate]
     FROM [Orders] AS [o]
     WHERE [c].[CustomerID] = [o].[CustomerID]
-    ORDER BY [o].[OrderDate] DESC)))
+    ORDER BY [o].[OrderDate] DESC))), '')
 FROM [Customers] AS [c]
 WHERE [c].[CustomerID] LIKE N'F%'
 """);

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

@@ -840,9 +840,9 @@ await AssertQueryScalar(
 
         AssertSql(
             """
-SELECT CAST(ISDATE(CONVERT(varchar(100), [o].[OrderDate])) AS bit)
+SELECT CAST(ISDATE(COALESCE(CONVERT(varchar(100), [o].[OrderDate]), '')) AS bit)
 FROM [Orders] AS [o]
-WHERE CAST(ISDATE(CONVERT(varchar(100), [o].[OrderDate])) AS bit) = CAST(1 AS bit)
+WHERE CAST(ISDATE(COALESCE(CONVERT(varchar(100), [o].[OrderDate]), '')) AS bit) = CAST(1 AS bit)
 """);
     }
 
@@ -888,9 +888,9 @@ await AssertQueryScalar(
 
         AssertSql(
             """
-SELECT CAST(ISNUMERIC(CONVERT(varchar(100), [o].[OrderDate])) ^ 1 AS bit) ^ CAST(1 AS bit)
+SELECT CAST(ISNUMERIC(COALESCE(CONVERT(varchar(100), [o].[OrderDate]), '')) ^ 1 AS bit) ^ CAST(1 AS bit)
 FROM [Orders] AS [o]
-WHERE ISNUMERIC(CONVERT(varchar(100), [o].[OrderDate])) <> 1
+WHERE ISNUMERIC(COALESCE(CONVERT(varchar(100), [o].[OrderDate]), '')) <> 1
 """);
     }
 

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

@@ -3436,7 +3436,7 @@ public override async Task Query_expression_with_to_string_and_contains(bool asy
             """
 SELECT [o].[CustomerID]
 FROM [Orders] AS [o]
-WHERE [o].[OrderDate] IS NOT NULL AND CONVERT(varchar(10), [o].[EmployeeID]) LIKE '%7%'
+WHERE [o].[OrderDate] IS NOT NULL AND COALESCE(CONVERT(varchar(10), [o].[EmployeeID]), '') LIKE '%7%'
 """);
     }
 
@@ -3488,7 +3488,7 @@ public override async Task Select_expression_other_to_string(bool async)
 
         AssertSql(
             """
-SELECT CONVERT(varchar(100), [o].[OrderDate]) AS [ShipName]
+SELECT COALESCE(CONVERT(varchar(100), [o].[OrderDate]), '') AS [ShipName]
 FROM [Orders] AS [o]
 WHERE [o].[OrderDate] IS NOT NULL
 """);

test/EFCore.Sqlite.FunctionalTests/BulkUpdates/NonSharedModelBulkUpdatesSqliteTest.cs

@@ -118,7 +118,7 @@ public override async Task Update_owned_and_non_owned_properties_with_table_shar
             """
 UPDATE "Owner" AS "o"
 SET "OwnedReference_Number" = length("o"."Title"),
-    "Title" = CAST("o"."OwnedReference_Number" AS TEXT)
+    "Title" = COALESCE(CAST("o"."OwnedReference_Number" AS TEXT), '')
 """);
     }
 

test/EFCore.Sqlite.FunctionalTests/BulkUpdates/NorthwindBulkUpdatesSqliteTest.cs

@@ -1328,12 +1328,12 @@ public override async Task Update_Where_Join_set_property_from_joined_single_res
         AssertExecuteUpdateSql(
             """
 UPDATE "Customers" AS "c"
-SET "City" = CAST(CAST(strftime('%Y', (
+SET "City" = COALESCE(CAST(CAST(strftime('%Y', (
     SELECT "o"."OrderDate"
     FROM "Orders" AS "o"
     WHERE "c"."CustomerID" = "o"."CustomerID"
     ORDER BY "o"."OrderDate" DESC
-    LIMIT 1)) AS INTEGER) AS TEXT)
+    LIMIT 1)) AS INTEGER) AS TEXT), '')
 WHERE "c"."CustomerID" LIKE 'F%'
 """);
     }
@@ -1362,12 +1362,12 @@ public override async Task Update_Where_Join_set_property_from_joined_single_res
         AssertExecuteUpdateSql(
             """
 UPDATE "Customers" AS "c"
-SET "City" = CAST(CAST(strftime('%Y', (
+SET "City" = COALESCE(CAST(CAST(strftime('%Y', (
     SELECT "o"."OrderDate"
     FROM "Orders" AS "o"
     WHERE "c"."CustomerID" = "o"."CustomerID"
     ORDER BY "o"."OrderDate" DESC
-    LIMIT 1)) AS INTEGER) AS TEXT)
+    LIMIT 1)) AS INTEGER) AS TEXT), '')
 WHERE "c"."CustomerID" LIKE 'F%'
 """);
     }

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

@@ -28,7 +28,7 @@ public override async Task Query_expression_with_to_string_and_contains(bool asy
             """
 SELECT "o"."CustomerID"
 FROM "Orders" AS "o"
-WHERE "o"."OrderDate" IS NOT NULL AND instr(CAST("o"."EmployeeID" AS TEXT), '7') > 0
+WHERE "o"."OrderDate" IS NOT NULL AND instr(COALESCE(CAST("o"."EmployeeID" AS TEXT), ''), '7') > 0
 """);
     }