Django Model Not Updating

Question

I'm trying to count the amount of times a user visits a page:

models.py:

class Request(models.Model):
    user = models.ForeignKey(User)
    view = models.CharField(max_length = 250)
    visits = models.PositiveIntegerField()

views.py

def daygaps(request,*a, **kw):

    request_counter = Request.objects.filter(
        user__username = request.user.username, view = 'daygaps')

    if request_counter:
        request_counter[0].visits += 1
        request_counter.update()

    else:
        Request.objects.create(
            user = request.user,
            visits = 1,
            view = 'daygaps')

When a new user visits the page for the first time, 'visits' gets set to = 1. Each subsequent visit should iterate the count. The "else" block works fine, however "visits" stays at 1 and does not change with each new request a user makes.

I've tried the ".save()" method, but that throws an error because "request_counter" is a queryset.

You should update a specific instance of query, Not all the query. Your query returns a queryset. Like lists. try updating `request_counter[0]` — alioguzhan, Dec 07 '16 at 18:30

Ivan · Accepted Answer · 2016-12-07T22:07:36.980

You could do something like this:

models.py

class Request(models.Model):
    user = models.ForeignKey(User)
    view = models.CharField(max_length = 250)
    visits = models.PositiveIntegerField(default=0)

views.py

def daygaps(request,*a, **kw):

    request_counter = Request.objects.get_or_create(
        user = request.user, view = 'daygaps')

    request_counter.visits += 1 # or =F('visits')+1 to avoid a race condition as suggested by Moses Koledoye
    request_counter.save()

OR

models.py

class Request(models.Model):
    user = models.ForeignKey(User)
    view = models.CharField(max_length = 250)
    visits = models.PositiveIntegerField(default=1)

views.py

def daygaps(request,*a, **kw):

    updated_count = Request.objects\
        .filter(user = request.user, view = 'daygaps')\
        .update(visits=F('visits')+1)

    if not updated_count:
        Request.objects.create(user = request.user, view = 'daygaps')

which avoids race conditions too and has an added advantage of not having to retrieve the object.

In general, I guess the second one is better if the update is simple enough to be implemented with F expressions.

Moses Koledoye · Answer 2 · 2016-12-07T18:41:00.023

Instead of using filter and indexing the list returned by the QuerySet, you could simply use .get to return the object:

from django.db.models import F

def daygaps(request,*a, **kw):
    ...
    request_counter = Request.objects.get(
        user__username = request.user.username, view = 'daygaps')
    request_counter.visits = F('visits') + 1
    request_counter.save()

You can wrap the logic in a try/except to handle DoesNotExist exceptions.

The F expression helps you manage race conditions. Read more: Updating attributes based on existing fields

Django Model Not Updating

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