远程服务器返回了意外的响应：（502）Azure WCF中的错误网关

Question

I've uploaded a service with the following contract.

[ServiceContract]
public interface Service
{
  [OperationContract]
  void CreateThing(Thing thing);
  [OperationContract]
  List<Thing> RetrieveThings();
}

When I call the creation method, everything works great, the instance is created in the DB and I get no errors. However, when I retrieve the elements, I get the error:

The remote server returned an unexpected response: (502) Bad Gateway.

The weird part is that when the list is empty (no elements in the DB), the operation goes well. Even more weird is that the operation against the DB works internally on the server and if I aggregate the names of the elements and send them out as a string or packaged in a string property of the class Thing , it works also!

This is what it looks like when it doesn't work:

public List<Thing> RetrieveThings()
{
  List<Thing> output;
  using (Context context = new Context())
    output = context.Things.ToList();
  return output;
}

This is what it looks like when it does work:

public List<Thing> RetrieveThings()
{
  List<Thing> output = new List<Thing>();
  using (Context context = new Context())
    foreach (Thing thing in context.Things.ToList())
      output.Add(new Thing {Id = thing.Id, Name = thing.Name});
  return output;
}

What is it I'm doing differently here (under the hood and not consciously)? Apparently I have access to the DB and I have the privileges. I can read off all the information, too. Still, I have to create copies of my objects for some reason. And I need to do so each-by-each and not with a LINQ query. Very confused...

Answer 1

I think it might be related to serialization.

context.Things.ToList()

This code looks like you are sending the EntityObject back from the service. What about trying using a POCO instead of using "Thing" interface? Or, you can cast/transform the object and return it?

context.Things.ToList()ToAnotherPlainClass()

Does your "Thing" class has only two properties? Are you able to return like that without looping?

public List<Thing> RetrieveThings()
{
  List<Thing> output;
  using (Context context = new Context())
    output = (from t in context.Things
               select new Thing() {
                  Id = t.Id, Name = t.Name
               }
             ).ToList();
  return output;
}

Have you checked this one on MSDN ? I haven't tested it yet but it seems like you need to apply [ApplyDataContractResolverAttribute] .

In most of my projects, I used to create the response model which is different from the actual entity so I didn't have the problem that you are having now. If you haven't tried ApplyDataContractResolverAttribute , I would say you should try that.