Fix run value converters that convert nulls for JSON columns

src/EFCore.Relational/Query/Internal/RelationalJsonUtilities.cs

@@ -89,8 +89,10 @@ void WriteJsonObject(Utf8JsonWriter writer, IComplexType complexType, object? ob
                 Check.DebugAssert(jsonPropertyName is not null);
                 writer.WritePropertyName(jsonPropertyName);
 
+                var jsonValueReaderWriter = property.GetJsonValueReaderWriter() ?? property.GetTypeMapping().JsonValueReaderWriter;
+
                 var propertyValue = property.GetGetter().GetClrValue(objectValue);
-                if (propertyValue is null)
+                if (propertyValue is null && jsonValueReaderWriter?.HandlesNullWrites != true)
                 {
                     if (!property.IsNullable)
                     {
@@ -101,7 +103,6 @@ void WriteJsonObject(Utf8JsonWriter writer, IComplexType complexType, object? ob
                 }
                 else
                 {
-                    var jsonValueReaderWriter = property.GetJsonValueReaderWriter() ?? property.GetTypeMapping().JsonValueReaderWriter;
                     Check.DebugAssert(jsonValueReaderWriter is not null, "Missing JsonValueReaderWriter on JSON property");
                     jsonValueReaderWriter.ToJson(writer, propertyValue);
                 }

src/EFCore.Relational/Query/RelationalShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.cs

@@ -3188,6 +3188,56 @@ private Expression CreateReadJsonPropertyValueExpression(
                     resultExpression = Convert(resultExpression, property.ClrType);
                 }
 
+                var converter = property.GetTypeMapping().Converter;
+                Expression nullExpression;
+                if (converter?.ConvertsNulls == true)
+                {
+                    var typeMappingExpression = Call(
+                        Convert(
+                            _parentVisitor.Dependencies.LiftableConstantFactory.CreateLiftableConstant(
+                                property,
+                                LiftableConstantExpressionHelpers.BuildMemberAccessLambdaForProperty(property),
+                                property.Name + "Property",
+                                typeof(IPropertyBase)),
+                            typeof(IReadOnlyProperty)),
+                        PropertyGetTypeMappingMethod);
+
+                    var converterExpression = (Expression)Property(typeMappingExpression, nameof(CoreTypeMapping.Converter));
+
+                    var converterType = converter.GetType();
+                    var typedConverterType = converterType.GetGenericTypeImplementations(typeof(ValueConverter<,>)).FirstOrDefault();
+                    if (typedConverterType != null)
+                    {
+                        if (converterExpression.Type != converter.GetType())
+                        {
+                            converterExpression = Convert(converterExpression, converter.GetType());
+                        }
+
+                        nullExpression = Invoke(
+                            Property(
+                                converterExpression,
+                                nameof(ValueConverter<object, object>.ConvertFromProviderTyped)),
+                            Default(converter.ProviderClrType));
+                    }
+                    else
+                    {
+                        nullExpression = Invoke(
+                            Property(
+                                converterExpression,
+                                nameof(ValueConverter.ConvertFromProvider)),
+                            Default(typeof(object)));
+                    }
+
+                    if (nullExpression.Type != property.ClrType)
+                    {
+                        nullExpression = Convert(nullExpression, property.ClrType);
+                    }
+                }
+                else
+                {
+                    nullExpression = Default(property.ClrType);
+                }
+
                 resultExpression = Condition(
                     Equal(
                         Property(
@@ -3196,7 +3246,7 @@ private Expression CreateReadJsonPropertyValueExpression(
                                 Utf8JsonReaderManagerCurrentReaderField),
                             Utf8JsonReaderTokenTypeProperty),
                         Constant(JsonTokenType.Null)),
-                    Default(property.ClrType),
+                    nullExpression,
                     resultExpression);
             }
 

src/EFCore.Relational/Update/ModificationCommand.cs

@@ -969,9 +969,9 @@ private void WriteJsonObject(
 #pragma warning disable EF1001 // Internal EF Core API usage.
             writer.WritePropertyName(jsonPropertyName);
 
-            if (propertyValue is not null)
+            var jsonValueReaderWriter = property.GetJsonValueReaderWriter() ?? property.GetTypeMapping().JsonValueReaderWriter;
+            if (propertyValue is not null || jsonValueReaderWriter?.HandlesNullWrites == true)
             {
-                var jsonValueReaderWriter = property.GetJsonValueReaderWriter() ?? property.GetTypeMapping().JsonValueReaderWriter;
                 Check.DebugAssert(jsonValueReaderWriter is not null, "Missing JsonValueReaderWriter on JSON property");
                 jsonValueReaderWriter.ToJson(writer, propertyValue);
             }

src/EFCore/Storage/Json/JsonConvertedValueReaderWriter.cs

@@ -32,13 +32,25 @@ public JsonConvertedValueReaderWriter(
         _converter = converter;
     }
 
+    /// <inheritdoc />
+    public override bool HandlesNullWrites => _converter.ConvertsNulls;
+
     /// <inheritdoc />
     public override TModel FromJsonTyped(ref Utf8JsonReaderManager manager, object? existingObject = null)
         => (TModel)_converter.ConvertFromProvider(_providerReaderWriter.FromJsonTyped(ref manager, existingObject))!;
 
     /// <inheritdoc />
     public override void ToJsonTyped(Utf8JsonWriter writer, TModel value)
-        => _providerReaderWriter.ToJson(writer, (TProvider)_converter.ConvertToProvider(value)!);
+    {
+        var convertedValue = _converter.ConvertToProvider(value);
+        if (convertedValue == null && !_providerReaderWriter.HandlesNullWrites)
+        {
+            writer.WriteNullValue();
+            return;
+        }
+
+        _providerReaderWriter.ToJson(writer, convertedValue);
+    }
 
     JsonValueReaderWriter ICompositeJsonValueReaderWriter.InnerReaderWriter
         => _providerReaderWriter;

src/EFCore/Storage/Json/JsonValueReaderWriter.cs

@@ -21,6 +21,15 @@ internal JsonValueReaderWriter()
     {
     }
 
+    /// <summary>
+    ///     If <see langword="true" />, then the nulls will be passed to the writer's <see cref="ToJson"/> method. Otherwise null
+    ///     values will always be written as <see langword="null"/>.
+    /// </summary>
+    /// <remarks>
+    ///     The default is <see langword="false" />.
+    /// </remarks>
+    public virtual bool HandlesNullWrites { get; } = false;
+
     /// <summary>
     ///     Reads the value from a UTF8 JSON stream or buffer.
     /// </summary>
@@ -48,7 +57,7 @@ internal JsonValueReaderWriter()
     /// </summary>
     /// <param name="writer">The <see cref="Utf8JsonWriter" /> into which the value should be written.</param>
     /// <param name="value">The value to write.</param>
-    public abstract void ToJson(Utf8JsonWriter writer, object value);
+    public abstract void ToJson(Utf8JsonWriter writer, object? value);
 
     /// <summary>
     ///     The type of the value being read/written.

src/EFCore/Storage/Json/JsonValueReaderWriter`.cs

@@ -15,8 +15,15 @@ public sealed override object FromJson(ref Utf8JsonReaderManager manager, object
         => FromJsonTyped(ref manager, existingObject)!;
 
     /// <inheritdoc />
-    public sealed override void ToJson(Utf8JsonWriter writer, object value)
-        => ToJsonTyped(writer, (TValue)value!);
+    public sealed override void ToJson(Utf8JsonWriter writer, object? value)
+    {
+        if (value == null && !HandlesNullWrites)
+        {
+            throw new ArgumentNullException(nameof(value));
+        }
+
+        ToJsonTyped(writer, (TValue)value!);
+    }
 
     /// <inheritdoc />
     public sealed override Type ValueType

test/EFCore.Relational.Specification.Tests/Query/AdHocJsonQueryRelationalTestBase.cs

@@ -693,6 +693,74 @@ public class JsonNestedType
 
     #endregion HasJsonPropertyName
 
+    #region Value converter equality null scalar
+
+    [ConditionalFact]
+    public virtual async Task Value_converter_equality_null_scalar()
+    {
+        var contextFactory = await InitializeNonSharedTest<Context37983>(
+            onConfiguring: b => b.ConfigureWarnings(ConfigureWarnings),
+            onModelCreating: m => m.Entity<Context37983.Entity>().ComplexProperty(e => e.Json, b =>
+            {
+                b.ToJson();
+
+                b.Property(j => j.IntToString).HasConversion(new Context37983_StringToIntConverter());
+            }),
+            seed: context =>
+            {
+                context.Set<Context37983.Entity>().Add(new Context37983.Entity
+                {
+                    Json = new Context37983.JsonComplexType
+                    {
+                        IntToString = null,
+                    }
+                });
+
+                return context.SaveChangesAsync();
+            });
+
+        await using var context = contextFactory.CreateDbContext();
+
+        TestSqlLoggerFactory.Clear();
+
+        var complexType = new Context37983.JsonComplexType
+        {
+            IntToString = null,
+        };
+
+        Assert.Equal(1, await context.Set<Context37983.Entity>().CountAsync(e => e.Json == complexType));
+    }
+
+    protected class Context37983(DbContextOptions options) : DbContext(options)
+    {
+        public DbSet<Entity> Entities { get; set; }
+
+        public class Entity
+        {
+            public int Id { get; set; }
+            public JsonComplexType Json { get; set; }
+        }
+
+        public class JsonComplexType
+        {
+            public int? IntToString { get; set; }
+        }
+    }
+
+    protected class Context37983_StringToIntConverter : ValueConverter<int?, string>
+    {
+        public Context37983_StringToIntConverter()
+            : base(
+                v => v == null ? "<null>" : v.ToString(),
+                v => int.Parse(v))
+        {
+        }
+
+        public override bool ConvertsNulls => true;
+    }
+
+    #endregion
+
     protected TestSqlLoggerFactory TestSqlLoggerFactory
         => (TestSqlLoggerFactory)ListLoggerFactory;
 

test/EFCore.Specification.Tests/ValueConvertersEndToEndTestBase.cs

@@ -168,38 +168,50 @@ public virtual async Task Can_insert_and_read_back_with_conversions(int[] valueO
         {
             var entity = new ConvertingEntity();
 
+            Add(context, entity);
+
             SetPropertyValues(context, entity, valueOrder[0], -1);
 
-            context.Add(entity);
             await context.SaveChangesAsync();
 
             id = entity.Id;
         }
 
         using (var context = CreateContext())
         {
-            SetPropertyValues(context, await context.Set<ConvertingEntity>().SingleAsync(e => e.Id == id), valueOrder[1], valueOrder[0]);
+            SetPropertyValues(context, await GetAsync(context, id), valueOrder[1], valueOrder[0]);
             await context.SaveChangesAsync();
         }
 
         using (var context = CreateContext())
         {
-            SetPropertyValues(context, await context.Set<ConvertingEntity>().SingleAsync(e => e.Id == id), valueOrder[2], valueOrder[1]);
+            SetPropertyValues(context, await GetAsync(context, id), valueOrder[2], valueOrder[1]);
             await context.SaveChangesAsync();
         }
 
         using (var context = CreateContext())
         {
-            SetPropertyValues(context, await context.Set<ConvertingEntity>().SingleAsync(e => e.Id == id), valueOrder[3], valueOrder[2]);
+            SetPropertyValues(context, await GetAsync(context, id), valueOrder[3], valueOrder[2]);
             await context.SaveChangesAsync();
         }
     }
 
-    private static void SetPropertyValues(DbContext context, ConvertingEntity entity, int valueIndex, int previousValueIndex)
+    protected virtual void Add(DbContext context, ConvertingEntity entity)
+        => context.Add(entity);
+
+    protected virtual Task<ConvertingEntity> GetAsync(DbContext context, Guid id)
+        => context.Set<ConvertingEntity>().SingleAsync(e => e.Id == id);
+
+    protected virtual PropertyEntry Property(DbContext context, ConvertingEntity entity, IProperty property)
+        => context.Entry(entity).Property(property);
+
+    protected virtual ITypeBase FindType(DbContext context)
+        => context.Model.FindEntityType(
+                typeof(ConvertingEntity))!;
+
+    private void SetPropertyValues(DbContext context, ConvertingEntity entity, int valueIndex, int previousValueIndex)
     {
-        var entry = context.Entry(entity);
-        foreach (var property in context.Model.FindEntityType(
-                     entity.GetType())!.GetProperties().Where(p => !p.IsPrimaryKey() && !p.IsShadowProperty()))
+        foreach (var property in FindType(context).GetProperties().Where(p => !p.IsPrimaryKey() && !p.IsShadowProperty()))
         {
             var testValues = (property.ClrType == typeof(string)
                 ? StringTestValues[property.GetValueConverter()!.ProviderClrType.UnwrapNullableType()]
@@ -211,7 +223,7 @@ private static void SetPropertyValues(DbContext context, ConvertingEntity entity
                 testValues[3] = null;
             }
 
-            var propertyEntry = entry.Property(property);
+            var propertyEntry = Property(context, entity, property);
 
             if (previousValueIndex >= 0
                 && property.FindAnnotation("Relational:DefaultValue") == null)

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

@@ -680,6 +680,20 @@ public override async Task Entity_splitting_with_owned_json()
 SELECT TOP(2) [m].[Id], [m].[PropertyInMainTable], [o].[PropertyInOtherTable], [m].[Json]
 FROM [MyEntity] AS [m]
 INNER JOIN [OtherTable] AS [o] ON [m].[Id] = [o].[Id]
+""");
+    }
+
+    public override async Task Value_converter_equality_null_scalar()
+    {
+        await base.Value_converter_equality_null_scalar();
+
+        AssertSql(
+            """
+@entity_equality_complexType='{"IntToString":"\u003Cnull\u003E"}' (Size = 34)
+
+SELECT COUNT(*)
+FROM [Entities] AS [e]
+WHERE [e].[Json] = @entity_equality_complexType
 """);
     }
 }

test/EFCore.SqlServer.FunctionalTests/Update/JsonUpdateJsonTypeSqlServerTest.cs

@@ -2497,9 +2497,9 @@ public override async Task Add_and_update_nested_optional_primitive_collection(b
 
         var parameterSize = value switch
         {
-            true => "1558",
-            false => "1555",
-            _ => "1557"
+            true => "1560",
+            false => "1557",
+            _ => "1559"
         };
 
         var updateParameter = value switch
@@ -2531,7 +2531,7 @@ public override async Task Add_and_update_nested_optional_primitive_collection(b
         AssertSql(
             @"@p0='[{""TestBoolean"":false,""TestBooleanCollection"":[],""TestByte"":0,""TestByteArray"":null,""TestByteCollection"":null,""TestCharacter"":""\u0000"",""TestCharacterCollection"":"
             + characterCollection
-            + @",""TestDateOnly"":""0001-01-01"",""TestDateOnlyCollection"":[],""TestDateTime"":""0001-01-01T00:00:00"",""TestDateTimeCollection"":[],""TestDateTimeOffset"":""0001-01-01T00:00:00+00:00"",""TestDateTimeOffsetCollection"":[],""TestDecimal"":0,""TestDecimalCollection"":[],""TestDefaultString"":null,""TestDefaultStringCollection"":[],""TestDouble"":0,""TestDoubleCollection"":[],""TestEnum"":0,""TestEnumCollection"":[],""TestEnumWithIntConverter"":0,""TestEnumWithIntConverterCollection"":[],""TestGuid"":""00000000-0000-0000-0000-000000000000"",""TestGuidCollection"":[],""TestInt16"":0,""TestInt16Collection"":[],""TestInt32"":0,""TestInt32Collection"":[],""TestInt64"":0,""TestInt64Collection"":[],""TestMaxLengthString"":null,""TestMaxLengthStringCollection"":[],""TestNullableEnum"":null,""TestNullableEnumCollection"":[],""TestNullableEnumWithConverterThatHandlesNulls"":null,""TestNullableEnumWithConverterThatHandlesNullsCollection"":[],""TestNullableEnumWithIntConverter"":null,""TestNullableEnumWithIntConverterCollection"":[],""TestNullableInt32"":null,""TestNullableInt32Collection"":[],""TestSignedByte"":0,""TestSignedByteCollection"":[],""TestSingle"":0,""TestSingleCollection"":[],""TestTimeOnly"":""00:00:00.0000000"",""TestTimeOnlyCollection"":[],""TestTimeSpan"":""0:00:00"",""TestTimeSpanCollection"":[],""TestUnsignedInt16"":0,""TestUnsignedInt16Collection"":[],""TestUnsignedInt32"":0,""TestUnsignedInt32Collection"":[],""TestUnsignedInt64"":0,""TestUnsignedInt64Collection"":[]}]' (Nullable = false) (Size = "
+            + @",""TestDateOnly"":""0001-01-01"",""TestDateOnlyCollection"":[],""TestDateTime"":""0001-01-01T00:00:00"",""TestDateTimeCollection"":[],""TestDateTimeOffset"":""0001-01-01T00:00:00+00:00"",""TestDateTimeOffsetCollection"":[],""TestDecimal"":0,""TestDecimalCollection"":[],""TestDefaultString"":null,""TestDefaultStringCollection"":[],""TestDouble"":0,""TestDoubleCollection"":[],""TestEnum"":0,""TestEnumCollection"":[],""TestEnumWithIntConverter"":0,""TestEnumWithIntConverterCollection"":[],""TestGuid"":""00000000-0000-0000-0000-000000000000"",""TestGuidCollection"":[],""TestInt16"":0,""TestInt16Collection"":[],""TestInt32"":0,""TestInt32Collection"":[],""TestInt64"":0,""TestInt64Collection"":[],""TestMaxLengthString"":null,""TestMaxLengthStringCollection"":[],""TestNullableEnum"":null,""TestNullableEnumCollection"":[],""TestNullableEnumWithConverterThatHandlesNulls"":""Null"",""TestNullableEnumWithConverterThatHandlesNullsCollection"":[],""TestNullableEnumWithIntConverter"":null,""TestNullableEnumWithIntConverterCollection"":[],""TestNullableInt32"":null,""TestNullableInt32Collection"":[],""TestSignedByte"":0,""TestSignedByteCollection"":[],""TestSingle"":0,""TestSingleCollection"":[],""TestTimeOnly"":""00:00:00.0000000"",""TestTimeOnlyCollection"":[],""TestTimeSpan"":""0:00:00"",""TestTimeSpanCollection"":[],""TestUnsignedInt16"":0,""TestUnsignedInt16Collection"":[],""TestUnsignedInt32"":0,""TestUnsignedInt32Collection"":[],""TestUnsignedInt64"":0,""TestUnsignedInt64Collection"":[]}]' (Nullable = false) (Size = "
             + parameterSize
             + @")
 @p1='7624'