Advantage of using IActionResult as result type in Actions

Question

What's the advantage or recommendation on using IActionResult as the return type of a WebApi controller instead of the actual type you want to return?

Most of the examples I've seen return IActionResult, but when I build my first site I exclusively use View Model classes as my return types.... now I feel like I did it all wrong!

Answer 1

The main advantage is that you can return error/status codes or redirects/resource urls.

For example:

public IActionResult Get(integer id)  {     var user = db.Users.Where(u => u.UserId = id).FirstOrDefault();      if(user == null)      {         // Returns HttpCode 404         return NotFound();     }      // returns HttpCode 200     return ObjectOk(user); } 

or

public IActionResult Create(User user)  {     if(!ModelState.IsValid)      {         // returns HttpCode 400         return BadRequest(ModelState);     }      db.Users.Add(user);     db.SaveChanges();      // returns HttpCode 201     return CreatedAtActionResult("User", "Get", new { id = user.Id} ); } 

Answer 2

The main advantage is that you can easily test your code using a mocking framework.

And as you build your controllers, you can easily change your return object as well. IActionResult is a interface and has many implementations like JsonResult, ViewResult, FileResult and so on.