Django exception while making an AJAX call

Question

I've developed a web app with Django. It makes an AJAX call (with jQuery's $.ajax) to update an image based on certain input text. The following code is used for the purpose:

$('img#diagram').attr('src', '/images/ajax/ajax_loader.gif');
$.ajax({
    type:       'POST',
    url:        '/draw/',
    data:       { 'diagram':  $('#diagram-text').val() },
    cache:      false,
    success:    function(mesg, txtStatus, XmlHttpRequest) {
        result = $.parseJSON(mesg);
        if (result['error']) {
            alert('An error was encountered: ' + result['error']);
        }
        else {
            $('img#diagram').attr('src', result['diagram_url']);
        }
    },
    error:      function(XmlHttpRequet, txtStatus, errorThrown) {
        alert('Failed to draw the diagram!\n' + errorThrown);
    },
    dataType:   'html'
});

It works properly i.e. updates the image after inputs are changed and the 'Draw' button is clicked.

Problem is, if I don't input anything, and click on the 'Draw' button, the AJAX loader image remains there. Now, nothing happens if I do either of the following:

Input some text and click on the 'Draw' button
Reload the page

In fact, the page doesn't get reloaded.

If I now stop the Django development server, I get the following error:

Exception happened during processing of request from ('127.0.0.1', 44166)
Unhandled exception in thread started by <function inner_run at 0x9f6d5dc>
Error in sys.excepthook:
Traceback (most recent call last):
  File "/usr/lib/python2.6/dist-packages/apport_python_hook.py", line 48, in apport_excepthook
    if not enabled():
TypeError: 'NoneType' object is not callable

Original exception was:
Traceback (most recent call last):
  File "/usr/local/lib/python2.6/dist-packages/django/core/management/commands/runserver.py", line 60, in inner_run
    run(addr, int(port), handler)
  File "/usr/local/lib/python2.6/dist-packages/django/core/servers/basehttp.py", line 721, in run
    httpd.serve_forever()
  File "/usr/lib/python2.6/SocketServer.py", line 226, in serve_forever
    self._handle_request_noblock()
  File "/usr/lib/python2.6/SocketServer.py", line 283, in _handle_request_noblock
    self.handle_error(request, client_address)
  File "/usr/lib/python2.6/SocketServer.py", line 335, in handle_error
    import traceback
ImportError: No module named traceback

Can anyone suggest anything? Of course I can put a validation to prevent empty strings. But why this actually happens, since AJAX is asynchronous?

silviomoreto · Accepted Answer · 2012-12-20 18:00:01Z

1

This happens when the client closes the connection before the server finished sending the data.

try the function done instead of success.

   $.ajax({
        url: "/draw/",
        type: "POST",
        data: { 'diagram':  $('#diagram-text').val() },
    }).done(function(data) {
        result = $.parseJSON(mesg);
        if (result['error']) {
          alert('An error was encountered: ' + result['error']);
        }
        else {
            $('img#diagram').attr('src', result['diagram_url']);
        }
    });

answered Dec 20, 2012 at 18:00

silviomoreto

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