ASP.NET Core Web API Automatic JSON Parameter Deserialization Not Working

Question

I've a simple controller that takes one parameter from the POST request body. Normally it should automatically deserialize it from JSON to the object type but it fails. When I try to deserialize it myself it works withot problems. Here is some code:

The controller (the documentCommand variable is null):

public async Task<IActionResult> Create([FromBody]CreateDocumentCommand documentCommand)
{
    if (documentCommand == null)
    {
        return StatusCode(403); //Deserialization fails, documentCommand is null
    }
    //we have to reach this :(
    return Json(documentCommand.Document.Id);
}

Here is how I serialize it and how I test if it will be able to deserialize it:

JsonSerializerSettings jsonSerializerSettings = new JsonSerializerSettings
{ 
    TypeNameHandling = TypeNameHandling.Auto,
    NullValueHandling = NullValueHandling.Ignore,
    MissingMemberHandling = MissingMemberHandling.Ignore
};
string serialized = JsonConvert.SerializeObject(item, jsonSerializerSettings);
CreateDocumentCommand deserialized = JsonConvert.DeserializeObject<CreateDocumentCommand>(serialized, jsonSerializerSettings);

In my CreateDocumentCommand class I have an interface property and when I remove the TypeNameHandling = TypeNameHandling.Auto it fails in the second example too.

Is there a way yo tell the MVC deserializer to take the TypeNameHandling into account? It seems to me that it skips it.

EDIT Some more code:

public class CreateDocumentCommand : Command, ICreateDocumentCommand
{
    public CreateDocumentCommand()
    {

    }

    public IDocument Document { get; set; }
}

MY SOLUTION: Added that ConcreteTypeConverter which I found at the link provided by Babak Naffas and made some changes because I was getting some circular reference exeptions. Also Added the [JsonConverter(typeof(ConcreteTypeConverter))] beefore the CreateDocumentCommand class.

public class ConcreteTypeConverter<T> : JsonConverter
{
    static bool read = false;

    public override bool CanConvert(Type objectType)
    {
        return typeof(T).IsAssignableFrom(objectType);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        serializer.TypeNameHandling = TypeNameHandling.Auto;
        serializer.NullValueHandling = NullValueHandling.Ignore;
        serializer.MissingMemberHandling = MissingMemberHandling.Ignore;
        return serializer.Deserialize<T>(reader);
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        serializer.Serialize(writer, value);
    }

    public override bool CanWrite
    {
        get
        {
            return false;
        }
    }

    public override bool CanRead
    {
        get
        {
            read = !read;
            return read;
        }
    }
}

What does `CreateDocumentCommand` look like? – Babak Naffas May 30 '18 at 17:28 — Babak Naffas, May 30 '18 at 17:28
I added it at the bottom of the question. – Kaloyan Manev May 30 '18 at 17:30 — Kaloyan Manev, May 30 '18 at 17:30

score 5 · Answer 1 · answered May 30 '18 at 17:43

If you want global setting then you can specify JsonSerializerSetting at application level using AddJsonOptions extension. Read it about here.

services.AddMvc()
.AddJsonOptions(opt =>
{
    if (opt.SerializerSettings != null)
    {
            opt.SerializerSettings.TypeNameHandling = TypeNameHandling.Auto,
            opt.SerializerSettings.NullValueHandling = NullValueHandling.Ignore,
            opt.SerializerSettings.MissingMemberHandling = MissingMemberHandling.Ignore
    }
});

AddJsonOptions is defined in Microsoft.AspNetCore.Mvc.Formatters.Json nuget package.

score 2 · Accepted Answer · answered May 30 '18 at 17:32

2

Your issue is the IDocument interface, which can't be deserialized out of the box as the deserializer can't know which concrete class to use.

Option 1 is to use a concrete class for the property
Option 2 is to use the solution from Casting interfaces for deserialization in JSON.NET

Also, make sure to create a unit test that takes the raw JSON that you'd be passing to your controller method and make sure it can be deserialized.

answered May 30 '18 at 17:32

Babak Naffas

12,395
3
34
49

Thanks a lot! Did some magic from the second bullet and managed to keep the interface! – Kaloyan Manev May 30 '18 at 21:11

ASP.NET Core Web API Automatic JSON Parameter Deserialization Not Working

2 Answers2