Cannot create new Django model object within Ajax post request

Question

This is kind of "I already lost x hours debugging this" kind of problem/question :(

Following jQuery js code is initiating POST request upon button click

$("#btn_create_tag").click(function(evt) {
$.post("/tag/createAjax", { 
    tagname: $("#txt_tag_name").val()       
    },
    function(data) {
    }
);
});

Django code that is performed on this call is:

@suppress_logging_output
@login_required
def createAjax(request):
    if request.is_ajax() and request.method == 'POST':
        tagName = request.POST["tagname"]
        new_tag = Tag()
        new_tag.name = tagName
        new_tag.save()
        print "new tag with id %s has been created" % new_tag.id

That code is executed successfully (I'm doing checks for empty or already existing name, but didn't wrote here to be more clear), but new Tag object is NOT created. I'm even getting ""new tag with id %s has been created" printed on devserver's prompt, and every time ID is increased for one, as suppossed to, but objects are not stored in db.

When I execute

new_tag = Tag()
new_tag.name = tagName
new_tag.save()

from Django shell, new Tag object is regulary created, but from jQuery request, it's not created.

Have any idea what's wront, what to check, how to debug this....

DB behind is PostgresSQL 8.3.

Any suggestion is more then welcome :)

Update:

I wrote UnitTest which is working:

class AjaxTestCase(TestCase):
    def testAjaxCreateTag(self):
        tagNum = Tag.objects.filter(name="TEST_TAG").count()
        self.assertEqual(tagNum, 0)
        c = Client()
        c.post('/lookup/tag/createAjax', {'tagname': 'TEST_TAG'}, HTTP_X_REQUESTED_WITH='XMLHttpRequest')
        tagNum = Tag.objects.filter(name="TEST_TAG").count()
        self.assertEqual(tagNum, 1)

Update2:

Hum, this morning, it seems that everything is working fine, but code hasn't changed. I don't like this at all :(

Manoj Govindan · Accepted Answer · 2010-08-21 12:31:56Z

1

This sounds very strange. Can you double check your database settings? Ensure that you are using the correct database inside settings.py? Also write an unit test to exercise the code using Django's test client. In your test method remember to send the HTTP_X_REQUESTED_WITH header for is_ajax() to work.

answered Aug 21, 2010 at 12:31

Manoj Govindan

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3 Comments

Jox Over a year ago

will try that. It really is strange, especially since django app is working correctly for a long time now. Will write unit test.

Manoj Govindan Over a year ago

The mystery deepens! Can you try an experiment? Change createAjax into a normal method that handles direct POST and not AJAX. See if it works (in dev and in unit test). Also see if there is any possibility of a transaction getting rolled back after the view is called.

Jox Over a year ago

Thanks a lot Manoj. After UTest succeeded, I ried again Ajax call and Tags are added fine. I don't like this syndrome of morning-after :( Still, I'll try to reproduce problem and find out that's wrong...

knutin · Accepted Answer · 2010-08-22 07:57:14Z

1

If you are using the TransactionMiddleware (see http://docs.djangoproject.com/en/dev/topics/db/transactions/), then not returning a HttpResponse of some sort will result in a crash and a rollback.

answered Aug 22, 2010 at 7:57

knutin

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1 Comment

Jox Over a year ago

Thanks for info. I'm using TransactionMiddleware. ALso, method is returning HttpResponse, but I didn't included that is code here (I should write down whole method).

Aviah Laor · Accepted Answer · 2010-08-21 12:01:12Z

0

try

new_tag=Tag(name=tagName)
new_tag.save()

BTW - you should sanitize the new tagname and not take it directly from the POST

answered Aug 21, 2010 at 12:01

Aviah Laor

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4 Comments

Jox Over a year ago

Thanks for answer. I already tried that and new_tag = Tag.objects.create(name=tagName) and it's not working :( I'm sanitizing tagName, but for sake of simpliticy of question on so, that part is left out.

Aviah Laor Over a year ago

can you catch the output sql to the DB?

Jox Over a year ago

how? It's ajax request, so djangologging won't do the thing (as far as I know). I'll try to log everything by PostgresSQL

Aviah Laor Over a year ago

For MySQL I use MySQL proxy that throws the sql to the console. Maybe you have a similar tool to Postgres?

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