Django Delete Data
Deleting data in Django is done with instance.delete() for a single row, or by calling delete() on a filtered queryset to remove many rows in one statement.
Deleting a Single Instance
Fetch the instance you want to remove, then call its delete() method. It returns a tuple: the total number of objects deleted, and a dictionary breaking that count down per model.
Example
from .models import Product
product = Product.objects.get(pk=7)
result = product.delete()
print(result) # (1, {'shop.Product': 1})Deleting a QuerySet
Calling delete() on a filtered queryset removes every matching row in a single query. Be careful - calling it on an unfiltered queryset removes the entire table's contents.
Example
# Remove every product that's been out of stock since before the cutoff
Product.objects.filter(in_stock=False, created_at__lt=cutoff_date).delete()on_delete and Related Rows
When a row is deleted and other rows point to it through a ForeignKey, the on_delete argument decides what happens to those related rows.
- CASCADE - delete the related rows too (e.g. delete a Product's Reviews along with it)
- PROTECT - block the delete and raise ProtectedError if related rows exist
- SET_NULL - set the foreign key to NULL (the field must allow null=True)
- SET_DEFAULT - set the foreign key to its default value
- DO_NOTHING - leave it to the database, rarely what you want
Note: delete() on both an instance and a queryset returns a tuple: the total number of objects deleted, and a dictionary breaking that count down per model - including anything removed through CASCADE.
Note: Product.objects.all().delete() removes every row in the table with no confirmation prompt. Always double-check your filter() conditions - and consider testing them with a matching .count() first - before calling delete().
Exercise: Django Delete Data
Which method removes a specific model instance's row from the database?
