How to force Web API to throw an error when receiving an unmapped field in the request json

Question

I'm building a REST API using Web API. The problem I am having is that the JSON serializer is not rejecting unmapped fields. Assuming I have a simple object like this: ``` public class MyClass { public bool MyBool { get; set; } public string MyString { get; set; } } ``` And I have a simple controller which accepts an object of this type in the body of a request ``` public void Post(MyClass instace) { ... } ``` Now, I post a request to the endpoint of this controller with the following JSON in the body of the request: { "MyBool":true, "MyString":"Valid", "InvalidField":"Invalid" } Currently, the controller will quietly accept this request, mapping true to MyBool, and "Valid" to MyString while ignoring the InvalidField. How can I change this so that an error is thrown whenever an invalid field is present?

Accepted Answer

I believe `Required` is not what you are looking for, since you are interested in extra fields that are present in the request. `Required` is for fields that are absent. You can read the JSON yourself and validate but to me that is a lot of work. So, piggy backing on binding is what something I would look at. I just wrote a small blog post to answer this question. Check it out http://lbadri.wordpress.com/2014/01/28/detecting-extra-fields-in-asp-net-web-api-request/.

How to force Web API to throw an error when receiving an unmapped field in the request json

Solution

Problem