Why I cannot use GET instead of POST?

Question

A very noob question, but I cannot completely understand why in the code below I can only use HttpPost(so it can run) and not HttpGet. Can someone please explain?

 [HttpPost]
        public ActionResult checkNumFocuses()
        {
            //stuff happening

            if (count == 3)
            {
                return Json(false);
            }
            else
            {
                return Json(true);
            }

        }

The above is my action method which returns true/false.

This is the ajax call on the fronted :

$.ajax({
      type: "POST",
      url: '@Url.Action("checkNumFocuses", "Home")',
      dataType: "json",
      success: successFunc,
      error: errorFunc
});
function successFunc(data, status) {
    if (data == false) {
        $(".alert").show();
        $('.btnfc').addClass('disabled');           
    }
}

I cannot undertant why if i delete the HttpPost attribute(so it is GET by default) and change the type in the ajax call from POST to GET.

What happens if you delete it? You're not clear in this regard. — tadman, Mar 20 '17 at 22:08
If I delete it and if i change the fronted part so the type is GET the error function is executed. Otherwise it works the way i pasted it. — Robert Ross, Mar 20 '17 at 22:10
Why exactly is it going to the error callback? error statuscode? unparsable response text? — Kevin B, Mar 20 '17 at 22:14
@NineBerry Failed to load resource: the server responded with a status of 500 (Internal Server Error) — Robert Ross, Mar 20 '17 at 22:16

Shyju · Accepted Answer · 2017-03-20T22:32:28.043

Yes. You can return Json from a GET method. But make sure to use the Json method overload which takes the JsonRequestBehavior enumeration.

Here you are explicitly saying you want to return json data from your GET action method.

public ActionResult checkNumFocuses()
{
  //stuff happening
   if (count == 3)
   {
       return Json(false,JsonRequestBehavior.AllowGet);
   }
   else
   {
       return Json(true,JsonRequestBehavior.AllowGet);
   }
}

Currently you are getting a 500 error response (instead of 200 OK with the valid data) because you are trying to return json data from the GET action method(without specifiying the JsonRequestBehavior enum value). Since the response is not 200 OK, It is going to your error handler part of your ajax call.

Ideally, GET operations should be idempotent . That means irrespective of how many times you execute it, it should not change any data (and returns the same response). In your case, your method is not udpating any data. So as long as you are OK that people can access this url in a browser tab and see the result, you may keep this as a GET method.

Usually in an ASP.NET MVC application, the GET method's are supposed to be returning a view/view response(markup) and typically the POST method does some processing on the posted form data/ajax data (Ex : updating some data etc) and return a response, which can be JSON. But if you really want to return Json data from your GET action method, You have to explicitly specify that using the above method we did

Of course, Web API's has a different concept (And implementation behind the scene)

Thanks. But, anyway, which of the two is best to be used in this case? And why? — Robert Ross, Mar 20 '17 at 22:17
In this case, you can use GET with the overload i mentioned in the answer.( Assuming that you are OK with people accessing the url directly in a tab and seeing the result) — Shyju, Mar 20 '17 at 22:23

score 1 · Answer 2 · answered Mar 20 '17 at 22:16

1

You can use a GET. But you also need to allow a GET in the JsonRequestBehavior

[HttpGet]
public ActionResult checkNumFocuses()
{
    ....
    return Json(true, JsonRequestBehavior.AllowGet);
}

answered Mar 20 '17 at 22:16

Thanks. But, anyway, which of the two is best to be used in this case? And why? – Robert Ross Mar 20 '17 at 22:17
1

If your changing data in the method (e.g. updating a database), then it should be a POST. Otherwise it can be either. – Mar 20 '17 at 22:21
For an update to an existing record, you should be using either a PUT or PATCH. POST should just be for creating a new record. – Rob W. Mar 20 '17 at 22:25

Why I cannot use GET instead of POST?

2 Answers2