Multiple actions matching the request - asp.net-web-api

Question

I have the following 2 routes defined in WebApiConfig.cs:
config.Routes.MapHttpRoute(
name: "DefaultApiWithAction",
routeTemplate: "api/{controller}/{action}/{id}"
);
config.Routes.MapHttpRoute(
name: "DefaultApi",
routeTemplate: "api/{controller}/{id}",
defaults: new { id = RouteParameter.Optional }
);
And on the server these two methods:
public IEnumerable<SampleForm> Get()
{
// do stuff
}
public IEnumerable<SampleForm> GetSampleFormsByState([FromUri]string[] state)
{
// do stuff
}
I am getting the error 'Multiple actions were found that match the request' and pointing out these two methods. The request is like this:
http://localhost/tracker/api/sampleform?state[]=pending&state[]=rejected&state[]=removed
So here's the interesting thing... if I change the second method to this:
public IEnumerable<SampleForm> GetSampleFormsByState(string state)
{
// do stuff
}
and make a request like:
http://localhost/tracker/api/sampleform?state=pending
There is no problem.
What is going on? What is it about the array that causes my routing to fail? What do I need to do?

Answer 1

string[] is a complex type. That is the very reason you had to use [FromUri] to get the binding to work. So, both the following methods can be selected by Web API to handle HTTP GET with complex type parameter binding.
public IEnumerable<SampleForm> Get() { }
public IEnumerable<SampleForm> GetSampleFormsByState([FromUri]string[] state) { }
Once you change one of the signatures to string, which is a simple type, you no longer have two GET methods for complex types and web API is able to select the action method without any confusion.
To get around this problem, you can define just one action method to handle GET like this.
public IEnumerable<SampleForm> Get([FromUri]string[] state) { }
In the action method, just check for state != null && state.Length > 0 to use the state data from the request in the filter.