MultipleObjectsReturned Django

Im trying to display a page that shows all the bookings in a Booking model on a page.

views.py

def bookings(request):
booking_list = get_object_or_404(Booking.objects.filter().order_by("-day"))
return render(request, 'roombooker/base.html', 'booking_list': booking_list)


models.py

class Booking(models.Model):
day = models.DateField(u'Booking Day',help_text=u'Day of Booking')
start_time = models.TimeField(u'Start Time', help_text=u'Start Time')
end_time = models.TimeField(u'End Time', help_text=u'End Time')
user = models.ForeignKey('User', on_delete=models.SET_NULL,null=True)
room = models.ForeignKey('Room', on_delete=models.SET_NULL,null=True)


urls.py

urlpatterns =[
url(r'^bookings/',views.bookings, name='bookings'),
]


There are currently 10 dummy entries in the db that I put in.

When I try to go to the bookings page however I get

MultipleObjectsReturned at /bookings/
get() returned more than one Booking -- it returned 10!

Which is what I want, I wanted 10 Booking objects. The idea was to pass it to the html for rendering.

How can I solve this error please?

Thanks

get_list_or_404

get_object_or_404

.get()

1 Answer
1

Like the name get_object_or_404 suggests, this is used to retrieve a single element. Behind the curtains, it calls .get() on the queryset, and in case there is no element, it raises an exception, or a specified by the documentation:

get_object_or_404

.get()

Calls get() on a given model manager, but it raises Http404 instead of the model's DoesNotExist exception.

get()

Http404

DoesNotExist

get_object_or_404 however has a slibing that returns a collection of elements: get_list_or_404 [Django-doc]. The difference is that here it raises an exception if the set is empty, and we obtain a collection of elements. Or like specified by the documentation:

get_object_or_404

get_list_or_404

Returns the result of filter() on a given model manager cast to a list, raising Http404 if the resulting list is empty.

filter()

Http404

So we can implement the view as:

def bookings(request):
booking_list = get_list_or_404(Booking.objects.filter().order_by("-day"))
return render(request, 'roombooker/base.html', 'booking_list': booking_list)

Note: if you do not want to .filter() the queryset on anything, it is advisable to use .all() instead.

.filter()

.all()

In case you do not want to materialize the queryset into a list, we can implement the check ourselves with:

from django.http import Http404

def bookings(request):
booking_list = Booking.objects.all().order_by("-day")
if not book_list:
raise Http404('No bookings found')
return render(request, 'roombooker/base.html', 'booking_list': booking_list)

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