MediaTypeFormatter issue in Self-Hosted ASPNET WebAPI

Question

I have implemented a custom MediaTypeFormatter in a SelfHosted AspNet WebAPI. I've used Unity.WebApi for dependency resolution. The controller classes only know about the interfaces implemented by the model classes, whereas, repositories give the concrete models as a result of actions.

The custom MediaTypeFormatter is inherited from BufferedMediaTypeFormatter as discussed here: http://www.asp.net/web-api/overview/formats-and-model-binding/media-formatters.

The problem is this media type formatter is not working. Even when I use to debug the code, the ReadFormStream method is never hit. Does someone know:

1. What could be the possible issue?
2. Do I need to tell the unity container for mapping of interfaces to model classes?
3. How would I get the reference to the dependency resolver inside the custom media type formatter?

Below is the code to add formatter:

var config = new SelfHostConfiguration("https://xxx.xxx.xxx.xxx:xxxx/");
config.Formatters.Add(new EntityTypeFormatter());

Below is the code for the EntityController:

    public class EntityController : ApiController
    {
        private readonly IEntitiesRepository repository = null;

        public EntityController(IEntitiesRepository repository)
        {
            if (repository == null)
            {
                throw new ArgumentNullException("repository");
            }

            this.repository = repository;
        }

        public IEnumerable<IEntity> Get()
        {
            return (IEnumerable<IEntity>)repository.Get();
        }
    }

Below is the code for the EntityRepository:

    public class EntitiesRepository : IEntitiesRepository
    {
        public IEnumerable<IEntity> Get()
        {
            return new Entities[]
            {
                new Entity
                { 
                    Prop1 = "value for property 1",
                    Prop2 = "value for property 2",
                    Prop3 = "value for property 3"
                },
                new Entity
                { 
                    Prop1 = "value for property 1",
                    Prop2 = "value for property 2",
                    Prop3 = "value for property 3"
                }
            };
        }
        public IEntity Get(long id)
        {
            return new Entity
                {
                    Prop1 = Convert.ToString(id),
                    Prop2 = "value for property 2",
                    Prop3 = "value for property 3"
                };
        }
    }

Below is the implementation of the EntityMediaTypeFormatter class:

public class EntityMediaTypeFormatter : BufferedMediaTypeFormatter 
    {
        public EntityMediaTypeFormatter()
            : base()
        {
            SupportedMediaTypes.Add(new MediaTypeHeaderValue("application/xml"));
            SupportedMediaTypes.Add(new MediaTypeHeaderValue("text/html"));
        }

        public override bool CanReadType(Type type)
        {
            if (type == null)
            {
                throw new ArgumentNullException("type");
            }

            if (type is IEntity)
            {
                return true;
            }
            else if (type.IsGenericType)
            {
                return type.GenericTypeArguments.Single(a => a.GetType().Equals(typeof(IEntity))) != null;
            }

            return false;
        }
        public override bool CanWriteType(Type type)
        {
            if (type == null)
            {
                throw new ArgumentNullException("type");
            }

            if (type is IEntity)
            {
                return true;
            }

            return false;
        }

        public override object ReadFromStream(Type type, Stream readStream, HttpContent content, IFormatterLogger formatterLogger)
        {
            if (type.IsInterface)
            {
                type = GetConcreteType(type);
            }

            return base.ReadFromStream(type, readStream, content, formatterLogger);
        }
        public override void WriteToStream(Type type, object value, Stream writeStream, HttpContent content)
        {
            //nothing special for now...
            base.WriteToStream(type, value, writeStream, content);
        }

        private Type GetConcreteType(Type type)
        {
            //TODO: Need to find a way to DependencyResolver to get the concrete type
            return typeof(Entity);
        }
    }

Thanking in advance for any help.

Answer 1

Looks to me like one of the existing formatters is taking priority over yours. Either clear the existing formatter collection before adding yours, or insert yours at position 0.