Base class as model in Web API - asp.net-web-api2

Question

Lets say I have the following class structure:
public abstract class BaseModel
{
public string Name {get;set;}
}
public class ExtendedOne : BaseModel
{
prop string Prop1 {get;set;}
}
public class ExtendedTwo : BaseModel
{
prop string AnotherProp {get;set;}
}
Then I have the follow Web API endpoint:
[Route("api/Test")
public IHttpActionResult Post(BaseModel model)
{
//Do work
}
I want a client to be able to post an instance of each of the extended classes to this endpoint.
When I try this the model is just null.
Is what I'm trying possible?

Answer 1

This isn't working because BaseModel is abstract. WebApi is trying to deserialize the model parameter as a BaseClass instance but it can't be instantiated because it is abstract. Web Api doesn't know anything about the derived classes. It only knows about JSON that it thinks represents a BaseClass instance which, again, is invalid because it is abstract.

Answer 2

Whether it is possible:
This should be possible by the architecture of webapi.
Web api is not really concerned about the class you define in the input. It receives data which is (mostly) in JSON format. If you look at the fiddler request, the name of the class is not sent to the web api. It will be a simple Json which will look like
POST http://localhost/api/Values/SomeMethod HTTP/1.1
User-Agent: Fiddler
Host: localhost:49946
Content-Length: 63
Content-Type: application/json; charset=utf-8
{
name: "Some Name"
}
The media formatters present in the pipeline will see that name property is present and will create an object of BaseModel. They will usually ignore additional properties and hence it should work well for the inherited classes.
Where it could go wrong:
From the code fragment included, we cant get a hint of why it is not working. Probably you need to include more code. However, one possibility is: if you use the derived class and do not set the Name property of the derived class.
Something like
var extended = new ExtendedOne{Prop1="Value1"}// Name is left out
In this case, in case json serializer is configured to omit nulls (Name in this case) the json sent to webapi could be something like
POST http://localhost/api/Values/SomeMethod HTTP/1.1
User-Agent: Fiddler
Host: localhost:49946
Content-Length: 63
Content-Type: application/json; charset=utf-8
{
prop1: "Value1"
}
Since Name is not present, webapi thinks it is something different, does not construct the model and sets model as null. You can detect what is the problem in your case by simply looking at what is being passed in the fiddler.