URL包含$ select时，自定义序列化程序不适用于oData 4的Web API 2

Question

I implemented a custom serializer by inheriting ODataEntityTypeSerializer. The serializer sets the value of "MessageStateName" by getting the name of BayStateEnum from the value of "MessageState". It works well only except when the URL contains "$select". I debugged the code and found it was executed and entityInstanceContext.EntityInstance had the correct value, but entityInstanceContext.EdmModel, which was of type System.Web.OData.Query.Expressions.SelectExpandBinder.SelectSome, still had an empty "MessageStateName".

public class CustomEntitySerializer : ODataEntityTypeSerializer
{
    public CustomEntitySerializer(ODataSerializerProvider serializerProvider)
        : base(serializerProvider)
    {
    }
    public override ODataEntry CreateEntry(SelectExpandNode selectExpandNode, EntityInstanceContext entityInstanceContext)
    {
        if (entityInstanceContext.EntityInstance is SmartLinkInfoModel)
        {
            var smartLinkInfo = entityInstanceContext.EntityInstance as SmartLinkInfoModel;
            if (smartLinkInfo.ModemIMEI != null)
            {
                smartLinkInfo.ModemIMEIString = "0x" + string.Join(string.Empty, smartLinkInfo.ModemIMEI.Select(b => (b - 48).ToString()));
            }
            if (smartLinkInfo.SmartLinkHardwareId != null)
            {
                smartLinkInfo.SmartLinkHardwareIdString = "0x" + string.Join(string.Empty, smartLinkInfo.SmartLinkHardwareId.Select(b => b.ToString()));
            }
            if (smartLinkInfo.XbeeSourceId != null)
            {
                smartLinkInfo.XbeeSourceIdString = "0x" + string.Join(string.Empty, smartLinkInfo.XbeeSourceId.Select(b => b.ToString()));
            }
        }
        else if (entityInstanceContext.EntityInstance is BayMessageModel)
        {
            var bayMessage = entityInstanceContext.EntityInstance as BayMessageModel;
            bayMessage.MessageStateName = Enum.GetName(typeof(BayStateEnum), bayMessage.MessageState);
        }
        return base.CreateEntry(selectExpandNode, entityInstanceContext);
    }
}

Answer 1

Your code to change the entityInstanceContext.EntityInstance is right, but it won't change the result of select, you can see

object propertyValue = entityInstanceContext.GetPropertyValue(structuralProperty.Name);

in ODataEntityTypeSerializer 's CreateStructuralProperty method, you should override this method, if the structuralProperty.Name is MessageStateName , then use (entityInstanceContext.EntityInstance as BayMessageModel).MessageStateName