How to write a custom parameter binding to construct an object either from body or from Uri's query

Mike has wrote this really good blog on writing a custom HttpParameterBinding at

https://blogs.msdn.com/b/jmstall/archive/2012/05/11/webapi-parameter-binding-under-the-hood.aspx

My blog just want to add a little bit complex example where you might want to have an action which looks like the following:

Code Snippet

8. public class HomeController : ApiController
9. {
10.     [HttpGet]
11.     [HttpPost]
12.     public HttpResponseMessage BindCustomComplexTypeFromUriOrBody(TestItem item)
13.     {
14.         return new HttpResponseMessage
15.         {
16.             Content = new StringContent(String.Format("BindCustomComplexType item.Name = {0}.", item.Name))
17.         };
18.     }
19. }
20.  
21. public class TestItem
22. {
23.     public string Name { get; set; }
24. }

Then the TestItem object can sometimes come from query like /?Name=Hongmei or coming from body. {Name:Hongmei}. It will be easy to write a custom parameter binding to do that.

Step 1: Write a custom FromUriOrFromBodyParameterBinding

Code Snippet

16. public class FromUriOrBodyParameterBinding : HttpParameterBinding
17.     {
18.         HttpParameterBinding _defaultUriBinding;
19.         HttpParameterBinding _defaultFormatterBinding;
20.  
21.         public FromUriOrBodyParameterBinding(HttpParameterDescriptor desc)
22.             : base(desc)
23.         {
24.             _defaultUriBinding = new FromUriAttribute().GetBinding(desc);
25.             _defaultFormatterBinding = new FromBodyAttribute().GetBinding(desc);
26.         }
27.  
28.         public override Task ExecuteBindingAsync(ModelMetadataProvider metadataProvider, HttpActionContext actionContext, CancellationToken cancellationToken)
29.         {
30.             if (actionContext.Request.Content != null )
31.             {
32.                 // we have something from the body, try that first
33.                 return _defaultFormatterBinding.ExecuteBindingAsync(metadataProvider, actionContext, cancellationToken);
34.             }
35.             else
36.             {
37.                 // we need to read things from uri
38.                 return _defaultUriBinding.ExecuteBindingAsync(metadataProvider, actionContext, cancellationToken);
39.             }
40.         }
41.  
42.     }

Step 2: Wire the FromUriOrFromBodyParameterBinding to the configuration

Code Snippet

52. public static HttpParameterBinding GetCustomParameterBinding(HttpParameterDescriptor descriptor)
53.         {
54.             if ( descriptor.ParameterType == typeof(TestItem))
55.             {
56.                 return new FromUriOrBodyParameterBinding(descriptor);
57.             }
58.  
59.             // any other types, let the default parameter binding handle
60.             return null;
61.         }

Code Snippet

26. config.ParameterBindingRules.Insert(0, GetCustomParameterBinding);