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?

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.