Newtonsoft.json serializing and deserializing base/inheirited where classes are from shared projects

Question

So I have two classes like the ones below. They are both in the same namespace and in the same shared project.

public class Person{
   public string Name{get;set;}
}

public class EmployedPerson : Person{
   public string JobTitle{get;set;}
}

When I serilize these items into rabbitmq I am serializing as the base class like so:

JsonSerializerSettings settings = new JsonSerializerSettings
{
   TypeNameAssemblyFormatHandling = TypeNameAssemblyFormatHandling.Simple,
   TypeNameHandling = TypeNameHandling.Objects
};
JsonConvert.SerializeObject(input, settings)

However when deserializing I run into issues. I would like to be able to do something like shown below where I deserialize as the base class and then check if it is a inheirited type.

Type check:

Person person = Deserialize<Person>(e.Body, Encoding.Unicode);
   if (person is EmployedPerson)
   {
    logger.LogInformation("This person has a job!");
    }

Deserialize settings:

   JsonSerializerSettings settings = new JsonSerializerSettings
   {
      TypeNameAssemblyFormatHandling = TypeNameAssemblyFormatHandling.Simple,
      TypeNameHandling = TypeNameHandling.Auto
   };

Deserialize logic:

    private static T Deserialize<T>(byte[] data, Encoding encoding) where T : class
    {
        try
        {
            using (MemoryStream stream = new MemoryStream(data))
            using (StreamReader reader = new StreamReader(stream, encoding))
                return JsonSerializer.Create(settings).Deserialize(reader, typeof(T)) as T;
        }
        catch (Exception e)
        {
            Type typeParameter = typeof(T);
            logger.LogError(LogEvent.SERIALIZATION_ERROR, e, "Deserializing type {@TypeName} failed", typeParameter.Name);
            logger.LogInformation(Encoding.UTF8.GetString(data));
            return default(T);
        }
    }

Result: The above code fails because the $type property contains the Assembly name and on each end of rabbitmq the assembly name is different because the classes are inside a shared project.

Example error:

Newtonsoft.Json.JsonSerializationException: Error resolving type specified in JSON 'Shared.Objects.EmployedPerson, Person.Dispatcher'. Path '$type', line 1, position 75. ---> System.IO.FileNotFoundException: Could not load file or assembly 'Person.Dispatcher, Culture=neutral, PublicKeyToken=null'. The system cannot find the file specified.

I think this might possibly be an answer to your issue: https://stackoverflow.com/questions/12381636/why-is-json-net-is-not-working-with-inheritance-while-deserializing — Ritwik Sen, Aug 28 '17 at 16:09
Your you could 1) write a [custom `SerializationBinder`](https://www.newtonsoft.com/json/help/html/SerializeSerializationBinder.htm). Writing your own binder that sanitizes deserialized types is also a good idea for security reasons as explained [here](https://stackoverflow.com/q/39565954/3744182). 2) Emit your own custom type property and parse it with a custom `JsonConverter` as shown, e.g., in [Json.Net Serialization of Type with Polymorphic Child Object](https://stackoverflow.com/q/29528648/3744182). — dbc, Aug 28 '17 at 16:12
I'm confused. Why is the assembly name different on each end of the queue if the types are in a shared project? — jebar8, Aug 28 '17 at 17:35
because shared projects don't create their own assemblies. They are assimilated into the project that is using it. — BillHaggerty, Aug 28 '17 at 17:59
For more on shared projects visit here: https://stackoverflow.com/questions/30634753/what-is-the-difference-between-a-shared-project-and-a-class-library-in-visual-st — BillHaggerty, Aug 28 '17 at 18:00
Hey anyone know how to handle Lists of complex types? They all Come through as "List`1".... — BillHaggerty, Aug 30 '17 at 12:23

BillHaggerty · Accepted Answer · 2017-09-08T11:33:58.017

Thank you @dbc, your suggestion to write a custom SerializationBinder is, as far as I can tell, the best solution to my problem.

I used the KnownTypesBinder as implemented at: https://www.newtonsoft.com/json/help/html/SerializeSerializationBinder.htm

KnownTypesBinder:

public class KnownTypesBinder : ISerializationBinder
    {
        public IList<Type> KnownTypes { get; set; }

        public Type BindToType(string assemblyName, string typeName)
        {
            return KnownTypes.SingleOrDefault(t => t.Name == typeName);
        }

        public void BindToName(Type serializedType, out string assemblyName, out string typeName)
        {
            assemblyName = null;
            typeName = serializedType.Name;
        }
    }

JsonSerializerSettings with the SerializationBinder set to an instance of KnownTypesBinder was used on both the serializing and deserializing endpoints. I probably only need it for the deserializing end, but put it in both for consistency.

settings = new JsonSerializerSettings
{
    TypeNameAssemblyFormatHandling = TypeNameAssemblyFormatHandling.Simple,
    TypeNameHandling = TypeNameHandling.Objects,
    SerializationBinder = new KnownTypesBinder()
};

After creating a settings object then I pass it into the JsonConvert serialization functions.

JsonConvert.DeserializeObject<T>(Encoding.Unicode.GetString(input), settings)

Also note that KnownTypes in KnownTypesBinder must be prepopulated with all of the non primitive types you will be deserializing.

Edit: I am currently not accepting my own answer because I have no idea how to handle List of complex types. For instance if a Person has a List and a List, what type do you return when the typeName is "List`1" and it could be either one.

Edit The following version of the KnownTypesBinder solved my issues related to Lists of objects.

public class KnownTypesBinder: ISerializationBinder
{
    public IList<Type> KnownTypes { get; set; }

    public Type BindToType(string assemblyName, string typeName)
    {
        return KnownTypes.SingleOrDefault(t => t.UnderlyingSystemType.ToString() == typeName);
    }

    public void BindToName(Type serializedType, out string assemblyName, out string typeName)
    {
        assemblyName = null;
        typeName = serializedType.UnderlyingSystemType.ToString();
    }
}

Newtonsoft.json serializing and deserializing base/inheirited where classes are from shared projects

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