Difference between Web API (standalone) and Web API ASP.NET MVC - asp.net-mvc

Question

I've created both an ASP.NET MVC project which includes the Web API and I created an empty project where only Web API was selected and I'm trying to understand why they are behaving differently.
Both of them from what I can tell have the routing definition defined as follows:
config.MapHttpAttributeRoutes();
config.Routes.MapHttpRoute(
name: "DefaultApi",
routeTemplate: "api/{controller}/{id}",
defaults: new { id = RouteParameter.Optional }
);
But I'd like to understand why the functions that are defined in the controller are behaving differently.
In my ASP.NET MVC Solution, I can create multiple functions under the one controller:
public IEnumerable<Product> GetAllProducts()
{
return products;
}
public IHttpActionResult GetProduct(int id)
{
var product = products.FirstOrDefault((p) => p.Id == id);
if (product == null)
{
return NotFound();
}
return Ok(product);
}
I don't have to add any attributes, well at least for gets and I can call individual function as:
http://localhost/api/test/GetProduct/1
http://localhost/api/test/GetProducts
In the Web API only solution, I had to define it as:
public IHttpActionResult HelloWorld()
{
return Ok("Hello World");
}
but the above will not work unless I add the [HttpGet] attribute to my HelloWorld function.
Also I don't seem to be able to define multiple functions within the one controller as it is done the in ASP.NET MVC Solution. Defining the same function as above just does not work or even if I define the functions below
[HttpGet]
public IHttpActionResult HelloWorld()
{
return Ok("Hello World");
}
[HttpGet]
public IHttpActionResult GetTime()
{
return Ok(DateTime.Now.ToString());
}
I get the following error:
<Error>
<Message>An error has occurred.</Message>
<ExceptionMessage>
Multiple actions were found that match the request: HelloWorld on type
MyProject.Controllers.TestController GetTime on type
MyProject.Controllers.TestController
</ExceptionMessage>
<ExceptionType>System.InvalidOperationException</ExceptionType>
<StackTrace>
at
System.Web.Http.Controllers.ApiControllerActionSelector.
ActionSelectorCacheItem.SelectAction(HttpControllerContext
controllerContext) at System.Web.Http.ApiController.
ExecuteAsync(HttpControllerContext controllerContext, CancellationToken
cancellationToken) at System.Web.Http.Dispatcher.
HttpControllerDispatcher.<SendAsync>d__15.MoveNext()
</StackTrace>
When I define a single function, it works but contrarily to a Web API defined in my ASP.NET MVC solution, when I call the below
http://localhost/api/test/HelloWorld
It doesn't seem to care what the function name is called as it will work if I call any of the following:
http://localhost/api/test
http://localhost/api/test/GoodBye
and will only fail if I provide an invalid controller name i.e.
http://localhost/api/mytest
Can you explain the difference between the 2 and ideally what do I have to do to get a stand-alone Web API to behave the same way as it does when defined in Asp.net MVC
Thanks.
UPDATE-1
Below are 2 good examples where the behavior is clearly different but I can't see why as both are called "Web API with ASP.NET MVC".
Creating Simple Service with ASP.NET MVC Web API to be accessed by Windows Store and Windows Phone Application
Getting Started with ASP.NET Web API 2 (C#)

Answer 1

Edit:
I'm sry at first I misunderstood your enquiry and therefore gave you the wrong answer to your question.
In Web Api you can't define two functions that serve the exact same path. But you can overload them like you would with Functions.
public IEnumerable<Product> GetAllProducts() {}
public IHttpActionResult GetProduct(int id) {}
These two function differ in so far that they serve different paths:
localhost/api/products/
localhost/api/products/{id}/
The following functions on the other hand both serve localhost/api/test/
[HttpGet]
public IHttpActionResult HelloWorld()
{
return Ok("Hello World");
}
[HttpGet]
public IHttpActionResult GetTime()
{
return Ok(DateTime.Now.ToString());
}
Your second concern has been the naming and mostly why you can't define HelloWorld() without [HttpGet]. That is because Web Api automatically maps functions that have a keyword such as Get or Delete as part of their name to the corresponding Http Function.
Adding the Http-Attribute is only needed if the function name does not conform to these naming conventions or shall serve multiple Http-Methods. It's described here
I hope your questions are now answered.
Orig:
The Default Routing and subsequent decision on what Function is to be executed is different between MVC and Web API
Default Web Api:
config.Routes.MapHttpRoute(
name: "DefaultApi",
routeTemplate: "api/{controller}/{id}",
defaults: new { id = RouteParameter.Optional }
);
Default Mvc:
config.Routes.MapHttpRoute(
name: "DefaultMvc",
routeTemplate: "/{controller}/{action}/{id}",
defaults: new { id = RouteParameter.Optional }
);
For Web Api the Routing is dependant on the controller name and further which Http-Method has been selected as well as the controller actually having a function the has been tagged with this method. Hence the and further Tags
Mvc on the other hand routes via the controller name and the action name to the desired functionality.
Web Api 2 adds further possibilies in letting you define AttributeRoutes. You may want to look further on this topic here and here