NewtonSoft.Json Serialize and Deserialize class with property of type IEnumerable<ISomeInterface>

I am trying to move some code to consume ASP.NET MVC Web API generated Json data instead of SOAP Xml.

I have run into a problem with serializing and deserializing properties of type:

IEnumerable<ISomeInterface>.

Here is a simple example:

public interface ISample{
  int SampleId { get; set; }
}
public class Sample : ISample{
  public int SampleId { get; set; }
}
public class SampleGroup{
  public int GroupId { get; set; }
  public IEnumerable<ISample> Samples { get; set; }
 }
}

I can serialize instances of SampleGroup easily with:

var sz = JsonConvert.SerializeObject( sampleGroupInstance );

However the corresponding deserialize fails:

JsonConvert.DeserializeObject<SampleGroup>( sz );

with this exception message:

"Could not create an instance of type JsonSerializationExample.ISample. Type is an interface or abstract class and cannot be instantated."

If I derive a JsonConverter I can decorate my property as follows:

[JsonConverter( typeof (SamplesJsonConverter) )]
public IEnumerable<ISample> Samples { get; set; }

Here is the JsonConverter:

public class SamplesJsonConverter : JsonConverter{
  public override bool CanConvert( Type objectType ){
    return ( objectType == typeof (IEnumerable<ISample>) );
  }

  public override object ReadJson( JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer ){
    var jA = JArray.Load( reader );
    return jA.Select( jl => serializer.Deserialize<Sample>( new JTokenReader( jl ) ) ).Cast<ISample>( ).ToList( );
  }

  public override void WriteJson( JsonWriter writer, object value, JsonSerializer serializer ){
    ... What works here?
  }
}

This converter solves the deserialization problem but I cannot figure how to code the WriteJson method to get serialization working again.

Can anybody assist?

Is this a "correct" way to solve the problem in the first place?

You don't need to use JsonConverterAttribute, just keep your model clean and use CustomCreationConverter instead, the code is simpler:

public class SampleConverter : CustomCreationConverter<ISample>
{
    public override ISample Create(Type objectType)
    {
        return new Sample();
    }
}

Then:

var sz = JsonConvert.SerializeObject( sampleGroupInstance );
JsonConvert.DeserializeObject<SampleGroup>( sz, new SampleConverter());

Documentation: Deserialize with CustomCreationConverter

It is quite simple and out of the box support provided by json.net, you just have to use the following JsonSettings while serializing and Deserializing:

JsonConvert.SerializeObject(graph,Formatting.None, new JsonSerializerSettings()
{
    TypeNameHandling =TypeNameHandling.Objects,
    TypeNameAssemblyFormat = System.Runtime.Serialization.Formatters.FormatterAssemblyStyle.Simple
});

and for Deserialzing use the below code:

JsonConvert.DeserializeObject(Encoding.UTF8.GetString(bData),type,
    new JsonSerializerSettings(){TypeNameHandling = TypeNameHandling.Objects}
);

Just take a note of the JsonSerializerSettings object initializer, that is important for you.

NewtonSoft.Json Serialize and Deserialize class with property of type IEnumerable<ISomeInterface>

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