LINQ3 ignors custom serializer if enum in expression has explicit type

Jonas_Jisander · 2025-04-08T09:13:43.043Z

I have a custom string-serializer for an enum of type ushort. I also have a class with a property of that enum type. When I query the database using a simple linq expression then the custom serializer is ignored. If I remove the explicit ushort declaration of the enum then the custom serializer is invoked.
This is a LINQ3 problem, LINQ2 did not ignore the serializer.
Below is an example of a test that I ran on the latest version of the driver

[Fact]
public void TestCustomSerializer()
{
    BsonSerializer.RegisterSerializer(typeof(MyEnum), new MyEnumTypeSerializer());
    var client = DriverTestConfiguration.Client;
    var db = client.GetDatabase("TestDb");
    db.DropCollection("TestA");
    var collection = db.GetCollection<TestA>("TestA");
    var testA = new TestA
    {
        EnumProperty = MyEnum.A
    };
    collection.InsertOne(testA);
    var result = collection.AsQueryable().FirstOrDefault(x => x.EnumProperty == testA.EnumProperty);
    result.Should().NotBeNull();
}

public class TestA
{
    [BsonId]
    public ObjectId MyId { get; set; }
    public MyEnum EnumProperty { get; set; }
}

public enum MyEnum : ushort // remove the explicit type and it will work
{
    A = 1
}

public class MyEnumTypeSerializer : StructSerializerBase<MyEnum>
{
    public override void Serialize(BsonSerializationContext context, BsonSerializationArgs args, MyEnum value)
    {
        BsonSerializer.Serialize(context.Writer, value.ToString());
    }
    public override MyEnum Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args)
    {
        var measurementValueType = (MyEnum)Enum.Parse(args.NominalType, BsonSerializer.Deserialize<string>(context.Reader));
        return measurementValueType;
    }
}

When debugging I end up in ConvertExpressionToFilterFieldTranslator.Translate. Here the type of the expression seems to be int and the enum underlying type is ushort which takes us in a different path in ConvertExpressionToFilterFieldTranslator.Translate

Is there a way around this?
I cannot change the enum to be an int, nor modify my TestA class!!

Boris_Dogadov · 2025-04-14T21:57:28.879Z

Jonas_Jisander:

LINQ2

Thanks @Jonas_Jisander for submitting this issue.
We are going to track it in CSHARP-5564