id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
11802	Wrong use of aggregation module may lead to non-deterministic bugs	AmirHabibi		"Assuming that an AJAX query posts (start, limit) for retrieving Polls (Django tutorial), writing the following code leads to request.POST problem.

{{{
#!python
from django.core import serializers
from django.http import HttpResponse
from django.db.models import Count
from polls import Poll

def respond(rows, totalCount):
    data = serializers.serialize('json', rows)
    response = ""{'success': true, 'totalCount':%d, 'rows':%s }"" % (totalCount, data)
    return HttpResponse(response, mimetype=""application/javascript"")


def listPolls(request):
    start = request.POST['start']
    limit = request.POST['limit']

    rows = Vehicle.objects.all()[start:start+limit]
    totalCount = Vehicle.objects.aggregate(Count('id'))
    
    return respond(rows, totalCount)
}}}

surprisingly, fixing the code to:
{{{
#!python
    totalCount = Vehicle.objects.aggregate(Count('id'))['id__count']
}}}
fixes the request.POST exception. The issue is that the django error report about request.POST not having a key named 'start' or 'limit' distracts the programmer to debugging the front end AJAX code rather than focusing on the Python bug. It also may indicate a more fundamental issue that exhibits random behavior.
"		closed	Database layer (models, ORM)	1.1		invalid			Unreviewed	0	0	0	0	0	0