5
Cannot call delete() after .distinct().
django
59414
Raise code
def delete(self):
"""Delete the records in the current QuerySet."""
self._not_support_combined_queries('delete')
if self.query.is_sliced:
raise TypeError("Cannot use 'limit' or 'offset' with delete().")
if self.query.distinct or self.query.distinct_fields:
raise TypeError('Cannot call delete() after .distinct().')
if self._fields is not None:
raise TypeError("Cannot call delete() after .values() or .values_list()")
del_query = self._chain()
# The delete is actually 2 queries - one to find related objects,
# and one to delete. Make sure that the discovery of relatedLinks to the raise (1)
https://github.com/django/django/blob/7cca22964c09e8dafc313a400c428242404d527a/django/db/models/query.py#L728Ways to fix
2
A QuerySet is iterable, and it executes its database query the first time you iterate over it. More information check
Queryset, as seen in the name, allows users to work tables in Database.
distinct - eliminates duplicate rows from the query results.
delete - performs an SQL delete query on all rows.
But one thing here, distinct('field_name') are only work in PostgreSQL.
To create a Django project:
django-admin startproject project_name
We need to create a user or simply let's create an admin user.
python manage.py createsuperuser
Need to write information about admin.
Username: admin Email address: Password: Password (again): The password is too similar to the username. This password is too short. It must contain at least 8 characters. This password is too common. Bypass password validation and create user anyway? [y/N]: y Superuser created successfully.
and next thing is to connect PostgreSQL with Django. Simple change DATABASE in settings.py. Check here
DATABASES = {
'default': {
'ENGINE': 'django.db.backends.postgresql_psycopg2',
'NAME': ‘<db_name>’,
'USER': '<db_username>',
'PASSWORD': '<password>',
'HOST': '<db_hostname_or_ip>',
'PORT': '<db_port>',
}
}
So, to get an error, we can use Django shell.
python manage.py shell
This command allows us to work with the database in the shell.
Then need to import the User table to our code.
>>>from django.contrib.auth.models import User
Define distinct value
>>>def_value = User.objects.distinct('is_staff')
>>> def_value
<QuerySet [<User: admin>]>
After distinct, if we want to delete that value
def_value.delete()
We will get an error
Traceback (most recent call last):
File "<console>", line 1, in <module>
File "C:\Users\ENVY\Desktop\python\Fiverr\Exceptions\test1\lib\site-packages\d
jango\db\models\query.py", line 728, in delete
raise TypeError('Cannot call delete() after .distinct().')
TypeError: Cannot call delete() after .distinct().
To fix that we can use a get to delete what we want.
>>> from django.contrib.auth.models import User
>>> a = User.objects.get()
>>> a
<User: admin>
>>> a.delete()
(1, {'auth.User': 1})
So simply to get an error we can use Django shell
