Custom serializer support for LINQ (#4138) should support STJ ExtensionData

[onionhammer]

Just by switching your custom serializer to inherit from 'CosmosSerializer' to 'CosmosLinqSerializer' this breaks any usage of ExtensionData in queries.

With custom serializer support, we should add detection of STJ-based 'ExtensionData' attribute in addition to the newtonsoft one. See #3777

Expected behavior
ExtensionData part of the path should be skipped in the generated SQL query:

i.e. MyObject.ExtensionData.MyCustomProperty > 42 becomes MyObject.MyCustomProperty > 42

Actual behavior
MyObject.ExtensionData.MyCustomProperty is retained, breaking the query, since STJ serializes MyCustomProperty to the root of the object.

Also, you cannot utilize CosmosLinqSerializer if you are trying to query against JSON ExtensionData.

Environment summary
SDK Version: 3.39.0-preview.0
OS Version (e.g. Windows, Linux, MacOSX): Windows 11

Additional context
#3777
#3834
#4138

@Maya-Painter

[Maya-Painter]

Hi @onionhammer, can you try handling extension data in your implementation of SerializeMemberName in your custom STJ serializer?

e.g.

  public override string SerializeMemberName(MemberInfo memberInfo)
  {
      JsonPropertyNameAttribute jsonPropertyNameAttribute = memberInfo.GetCustomAttribute<JsonPropertyNameAttribute>(true);

      string memberName = jsonPropertyNameAttribute != null && !string.IsNullOrEmpty(jsonPropertyNameAttribute.Name)
          ? jsonPropertyNameAttribute.Name
          : memberInfo.Name;

      // Handle ExtensionData members
      System.Text.Json.Serialization.JsonExtensionDataAttribute jsonExtensionDataAttribute = 
          memberInfo.GetCustomAttribute<System.Text.Json.Serialization.JsonExtensionDataAttribute>(true);
      if(jsonExtensionDataAttribute != null)
      {
          return null;
      }

      return memberName;
  }

[onionhammer]

@Maya-Painter Good idea, that does workaround this issue.

Can the base method be decorated as nullable?

e.g.

    public abstract string? SerializeMemberName(MemberInfo memberInfo);

[Maya-Painter]

Since the string type is inherently nullable, I don't know if this adds any value.

I will add the ExtensionData handling code to the sample custom serializers for others to use as reference, however. Thanks for pointing this out.