当HTTP-POST具有主体时，url参数为null

Question

This is self-hosted RESTful MVC4 Web API, the only route is api/{controller}/{state} . When I send an HTTP-POST that has a body, the state argument comes in null. If I remove the body the state variable is present.

The way I thought it worked for HTTP-POST was that the url parameters get mapped then the body gets serialized into the extra parameter, which in this case is data parameter. The content is just string data which I had to write a custom MediaTypeFormatter (which I thought was odd it couldn't handle a regular string).

Here is my controller signature

public class MyController : ApiController
{
    public void Post(string state, string data)
    {
    }
}

Has anyone seen this behavior before or can explain to me why having a body present is affecting my url parameter?

Answer 1

One Solution: I tried changing data parameter into a complex type (Just a class with a public property) and sending the content as text/xml instead of text/plain and it worked as expected. The state parameter wasn't null and I had my strongly typed object with the data. I suppose MVC wants to have something to deserialize like XML or JSON for the http-request body...

More Research: I've had the chance to run some more tests. If the body of a post is XML/JSON it will first try to map the properties of the body-object to the method parameters like so. If still has unmapped properties then it will match the remaining properties to the properties of any strongly-typed objects in the method parameters

PostMethod(string p1, string p2, myClass obj) // if myClass has a p3 property it will be mapped from the xml body.
{
}

// xml in body of http-post
<Xml>
   </p1>
   </p2>
   </p3>
</Xml>

If all the parameters were not mapped, then it will attempt to map the url parameters. To relate it directly to my initial problem. The best and easiest solution I see at this time is to send text/xml like this.

PostMethod(string state, string data)
{
}

<data>put data here</data>

Urlencoded key/value pairs also work very well.

var r = client.PostAsync(url, new StringContent("data=Something", Encoding.UTF8, "application/x-www-form-urlencoded"));

My best guess is that the key/value nature of JSON and XML, FormEncoded help it to map to parameters so that is why it doesn't like plain strings.

This sure gave me a headache and I find the MVC4 documentation to be rather scarce (its still in beta), but I hope this can help someone else who may have the same problem.