How To Check If An Element Is Present In A Django Queryset?

Is it like a regular python set? Suppose I have the following queryset entry_set = Entry.objects.all() How do I check if Entry Object e is present in entry_set?

Solution 1:

You can use the following code:

if e in Entry.objects.all():
        #do something

Or the best approach:

if Entry.objects.filter(id=e.id).exists():
        #do something

Solution 2:

The best approach, according to Django documentation: https://docs.djangoproject.com/en/2.1/ref/models/querysets/#exists

if Entry.objects.filter(id=item.id).exists():
    # Do something

But you can also do:

if item in Entry.objects.all():
    # Do something

Although this approach is the worser as possible. Because it will loop over the whole Queryset pulling elements from the database one by one, compared to the other approach that is almost everything done in the Database level.

If you have a list of ids or a Queryset others approaches would be use __in

Example with a Queryset:

query_ids = other_queryset.values_list('field_id', flat=True)
if Entry.objects.filter(id__in=query_ids).exists():
    # Do something

Or if you have a list of ids:

if Entry.objects.filter(id__in=[1, 2, 3, 4, 5]).exists():
    # Do something

Keep in mind that every time that you do len(queryset), item in queryset or list(queryset) you decrees heavily the performance of Django. I already see cases where by avoiding this practices We improved dozens of seconds in an application.

Solution 3:

You can use in operator:

entry_set = Entry.objects.all()
if an_entry in entry_set:
    # The element present.

Solution 4:

You can just filter the queryset on the basis of a unique key present in the Entry model. Say, that key is id, your code would become:

is_present = Entry.objects.filter(id=e.id)
if is_present:
    print"Present"else:
    print"Not Present"