Failed to serialize the response in Web API with J

Question

I am working with ASP.NET MVC 5 Web Api. I want consult all my users.

I wrote api/users and I receive this:

"The 'ObjectContent`1' type failed to serialize the response body for content type 'application/json; charset=utf-8'"

In WebApiConfig, already I added these lines:

HttpConfiguration config = new HttpConfiguration();
config.Formatters.XmlFormatter.SupportedMediaTypes.Remove(appXmlType);
config.Formatters.JsonFormatter.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore; 

But it still doesn't work.

My function for return data is this:

public IEnumerable<User> GetAll()
{
    using (Database db = new Database())
    {
        return db.Users.ToList();
    }
}

Answer 1

To add to jensendp's answer:

I would pass the entity to a user created model and use the values from that entity to set the values in your newly created model. For example:

public class UserInformation {
   public string Name { get; set; }
   public int Age { get; set; }

   public UserInformation(UserEntity user) {
      this.Name = user.name;
      this.Age = user.age;
   }
}

Then change your return type to: IEnumerable<UserInformation>

Answer 2

public class UserController : ApiController
{

   Database db = new Database();

   // construction
   public UserController()
   {
      // Add the following code
      // problem will be solved
      db.Configuration.ProxyCreationEnabled = false;
   }

   public IEnumerable<User> GetAll()
    {
            return db.Users.ToList();
    }
}

Answer 3

There's also this scenario that generate same error:

In case of the return being a List<dynamic> to web api method

Example:

public HttpResponseMessage Get()
{
    var item = new List<dynamic> { new TestClass { Name = "Ale", Age = 30 } };

    return Request.CreateResponse(HttpStatusCode.OK, item);
}

public class TestClass
{
    public string Name { get; set; }
    public int Age { get; set; }
}

So, for this scenario use the [KnownTypeAttribute] in the return class (all of them) like this:

[KnownTypeAttribute(typeof(TestClass))]
public class TestClass
{
    public string Name { get; set; }
    public int Age { get; set; }
}

This works for me!

Answer 4

When it comes to returning data back to the consumer from Web Api (or any other web service for that matter), I highly recommend not passing back entities that come from a database. It is much more reliable and maintainable to use Models in which you have control of what the data looks like and not the database. That way you don't have to mess around with the formatters so much in the WebApiConfig. You can just create a UserModel that has child Models as properties and get rid of the reference loops in the return objects. That makes the serializer much happier.

Also, it isn't necessary to remove formatters or supported media types typically if you are just specifying the "Accepts" header in the request. Playing around with that stuff can sometimes make things more confusing.

Example:

public class UserModel {
    public string Name {get;set;}
    public string Age {get;set;}
    // Other properties here that do not reference another UserModel class.
}

Answer 5

While all these answers above are correct, one may want to check the InnerException > ExceptionMessage.

If it says something like this "The ObjectContext instance has been disposed and can no longer be used for operations that require a connection.". This could be an issue because of default behavior of the EF.

By assigning LazyLoadingEnabled = false in your DbContext constructor will do the trick.

public class MyDbContext : DbContext
{
  public MyDbContext()
  {
    this.Configuration.LazyLoadingEnabled = false;
  }
}

For more detailed reading about EagerLoading and LazyLoading behavior of EF refer this MSDN Article.

Answer 6

I resolved it using this code to WebApiConfig.cs file

var json = config.Formatters.JsonFormatter;
json.SerializerSettings.PreserveReferencesHandling = Newtonsoft.Json.PreserveReferencesHandling.Objects; 
config.Formatters.Remove(config.Formatters.XmlFormatter);