How to prevent Json.NET from using the Entity Framework proxy type name?

Question

In my design I have a class that has a property whose type can be inherited from:

public class Feed
{
    ...
    [JsonProperty(TypeNameHandling = TypeNameHandling.Auto)]
    public FeedSource Source { get; set; }
    ...
}

public abstract class FeedSource { ... }

public class CsvSource : FeedSource { ... }

public class DbSource : FeedSource { ... }

I'm using the Entity Framework to load and store this object to a database and I'm using Json.NET to serialize this object into JSON for further processing.

The problem I stumbled on is that the $type property is containing the typename of the EF proxy instead of the "real" typename. So instead of:

$type: "System.Data.Entity.DynamicProxies.CsvSource_0B3579D9BE67D7EE83EEBDDBFA269439AFC6E1122A59B4BB81EB1F0147C7EE12"

which is meaningless to other clients, I would like to get:

$type: "MyNamespace.CsvSource"

in my JSON.

What's the best way to achieve this?

Answer 1

Another way which doesn't require you to make changes to your EF configuration is to use a custom SerializationBinder, e.g.:

class EntityFrameworkSerializationBinder : SerializationBinder
{
    public override void BindToName(Type serializedType, out string assemblyName, out string typeName)
    {
        assemblyName = null;

        if (serializedType.Namespace == "System.Data.Entity.DynamicProxies")
            typeName = serializedType.BaseType.FullName;
        else
            typeName = serializedType.FullName;
    }

    public override Type BindToType(string assemblyName, string typeName)
    {
        throw new NotImplementedException();
    }
}

Usage:

string json = JsonConvert.SerializeObject(entityFrameworkObject, new JsonSerializerSettings { TypeNameHandling = TypeNameHandling.All, Binder = new EntityFrameworkSerializationBinder() });

Answer 2

You can do two things:

• disabling tracking proxies, by setting ProxyCreationEnabled to false. You can find this property in your context's Configuration property. If you use a context for a single GetXxx method, you can do it without interfering other context instanced.

• using the AsNoTracking() extension method when you recover your entity, like this:

  MyContext.MyTable.AsNoTracking(). // rest of the query here

This indicates that you don't want a tracking proxy for your entity, so you'll get the entity class. This has no interference with the afore mentioned configuration.