How to add an model instance to a django queryset?

It seems like a django queryset behaves somehow like a python list.

But it doesn't support list's .append() method as I know.

What I want to do is like:

from my_django_app.models import MyModel queryset = MyModel.objects.none() queryset.append(MyModel.objects.first()) ## no list's .append() method! 

Is there any way to add an model instance to an existing queryset?

4 Answers

You can also use the | operator to create a union:

queryset = MyModel.objects.none() instance = MyModel.objects.first() queryset |= MyModel.objects.filter(pk=instance.pk) 

But be warned that this will generate different queries depending on the number of items you append this way, making caching of compiled queries inefficient.

No. A queryset is a representation of a query - hence the name - not an arbitrary collection of instances.

If you really need an actual queryset rather than a list, you could try accumulating the IDs of the objects you need and then getting the objects via an __in query:

list_of_ids = [] list_of_ids.append(my_id) ... queryset = MyModel.objects.filter(id__in=list_of_ids) 

This isn't very efficient, though.

This can be done using union. After doing this, the type of the result can be seen as <class 'django.db.models.query.QuerySet'>. So two querysets can be combined. Lets see an example.

query1 = User.objects.filter(is_active=True) query2 = User.objects.filter(is_active=False) combined_query = query1.union(query2) print (type(combined_query)) 

The above program will print result as below, confirming it is a queryset

<class 'django.db.models.query.QuerySet'> 

So basically Django executes the below query for union.

(SELECT "auth_user"."id", "auth_user"."password", "auth_user"."last_login", "auth_user"."is_superuser", "auth_user"."username", "auth_user"."first_name", "auth_user"."last_name", "auth_user"."email", "auth_user"."is_staff", "auth_user"."is_active", "auth_user"."date_joined" FROM "auth_user" WHERE "auth_user"."is_active" = True) UNION (SELECT "auth_user"."id", "auth_user"."password", "auth_user"."last_login", "auth_user"."is_superuser", "auth_user"."username", "auth_user"."first_name", "auth_user"."last_name", "auth_user"."email", "auth_user"."is_staff", "auth_user"."is_active", "auth_user"."date_joined" FROM "auth_user" WHERE "auth_user"."is_active" = False) 

This also means that there will be error(django.db.utils.ProgrammingError: each UNION query must have the same number of columns) if union is tried with two different tables.

Queryset is not a list

So

to_list = queryset.values() 

To combine queryset

from itertools import chain result_queryset = list(chain(queryset1, queryset2)) 

or

querysets = [queryset1, queryset2] result_queryset = list(chain(*querysets))