Simply add an attribute to the controller action

[Route("product/{productId}/customer")]
public IQueryable<Product> GetProductsByCustomer(int productId) 
{ 
    //action code goes here 
}

this will be queried as /product/1/customer and productId=1 will be sent to the controller action.

Make sure the one within '{ }' and the action parameter are same. productId in this case.

before using this, you have to specify that you are using Attribute Routing by:

public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {
        config.MapHttpAttributeRoutes();
    }
}

In cases where you need a common portion of the route for all routes within a controller, RoutePrefix attribute is used.

In the below example, api/students part of the code is common and so we can define RoutePrefix and avoid using it repeatedly.

[RoutePrefix("api/students")]
public class StudentController : ApiController
{
[Route("")]
public IEnumerable<Student> Get() 
{
    //action code goes here 
}

[Route("{id:int}")]
public Student Get(int id) 
{
    //action code goes here 
}

[Route("")]
public HttpResponseMessage Post(Student student) 
{
    //action code goes here 
}

}