Difference Between $.getJSON() and $.ajax() in jQuery

Question

I am calling an ASP.NET MVC action

public JsonResult GetPatient(string patientID)
{
...

from JavaScript using jQuery. The following call works

$.getJSON(
'/Services/GetPatient',
{ patientID: "1" },
function(jsonData) {
  alert(jsonData);
});

whereas this one does not.

$.ajax({
  type: 'POST',
  url: '/Services/GetPatient',
  data: { patientID: "1" },
  contentType: 'application/json; charset=utf-8',
  dataType: 'json',
  success: function(jsonData) {
    alert(jsonData);
  },
  error: function() {
    alert('Error loading PatientID=' + id);
  }
});

Both reach the action method, but the patientID value is null w/ the $.ajax call. I'd like to use the $.ajax call for some of the advanced callbacks.

Any thoughts appreciated.

Answer 1

The only difference I see is that getJSON performs a GET request instead of a POST.

Answer 2

Replace

data: { patientID: "1" },

with

data: "{ 'patientID': '1' }",

Further reading: 3 mistakes to avoid when using jQuery with ASP.NET

Answer 3

.getJson is simply a wrapper around .ajax but it provides a simpler method signature as some of the settings are defaulted e.g dataType to json, type to get etc

N.B .load, .get and .post are also simple wrappers around the .ajax method.

Answer 4

contentType: 'application/json; charset=utf-8'

Is not good. At least it doesnt work for me. The other syntax is ok. The parameter you supply is in the right format.

Answer 5

Content-type

You don't need to specify that content-type on calls to MVC controller actions. The special "application/json; charset=utf-8" content-type is only necessary when calling ASP.NET AJAX "ScriptServices" and page methods. jQuery's default contentType of "application/x-www-form-urlencoded" is appropriate for requesting an MVC controller action.

More about that content-type here: http://weblogs.asp.net/scottgu/archive/2007/04/04/json-hijacking-and-how-asp-net-ajax-1-0-mitigates-these-attacks.aspx

Data

The data is correct as you have it. By passing jQuery a JSON object, as you have, it will be serialized as patientID=1 in the POST data. This standard form is how MVC expects the parameters.

You only have to enclose the parameters in quotes like "{ 'patientID' : 1 }" when you're using ASP.NET AJAX services. They expect a single string representing a JSON object to be parsed out, rather than the individual variables in the POST data.

JSON

It's not a problem in this specific case, but it's a good idea to get in the habit of quoting any string keys or values in your JSON object. If you inadvertently use a JavaScript reserved keyword as a key or value in the object, without quoting it, you'll run into a confusing-to-debug problem.

Conversely, you don't have to quote numeric or boolean values. It's always safe to use them directly in the object.

So, assuming you do want to POST instead of GET, your $.ajax() call might look like this:

$.ajax({
  type: 'POST',
  url: '/Services/GetPatient',
  data: { 'patientID' : 1 },
  dataType: 'json',
  success: function(jsonData) {
    alert(jsonData);
  },
  error: function() {
    alert('Error loading PatientID=' + id);
  }
});