How to create GeneratedField with lookup from settings file?
While using Django 5.1, I'm trying to create a GeneratedField which should return True or False depending on which file has been uploaded. The model will accept both image- and video files. I want to do this in order to be able to filter on e.g. CampMedia.objects.filter(is_image=True).
# models.py
from django.conf import settings
from django.db import models
from django.db.models import Case, Q, When
class CampMedia(models.Model):
media = models.FileField(upload_to="camps")
is_image = models.GeneratedField(
expression=Case(
When(
condition=Q([Q(media__endswith=ext) for ext in settings.VALID_IMAGE_FILETYPES], Q.OR),
then=True,
),
default=False,
),
output_field=models.BooleanField(),
db_persist=True,
)
# settings.py
VALID_IMAGE_FILETYPES = ["png", "jpg", "jpeg", "gif", "webp"]
This is what's generated in the migration file:
# migrations/0007_image.py
from django.db import migrations, models
class Migration(migrations.Migration):
dependencies = [
("camps", "0006_auto"),
]
operations = [
migrations.AddField(
model_name="campmedia",
name="image",
field=models.GeneratedField(
db_persist=True,
expression=models.Case(
models.When(
condition=models.Q(
[
models.Q(("media__endswith", "png")),
models.Q(("media__endswith", "jpg")),
models.Q(("media__endswith", "jpeg")),
models.Q(("media__endswith", "gif")),
models.Q(("media__endswith", "webp")),
],
"OR",
),
then=True,
),
default=False,
),
output_field=models.BooleanField(),
),
),
]
However, this generates this error when running python manage.py migrations:
$ ./manage.py migrate camps
Operations to perform:
Apply all migrations: camps
Running migrations:
Applying camps.0007_image...Traceback (most recent call last):
File "C:\xampp\htdocs\manage.py", line 15, in <module>
execute_from_command_line(sys.argv)
File "C:\Users\Owner\.virtualenvs\p1pRKLs2\Lib\site-packages\django\core\management\__init__.py", line 442, in execute_from_command_line
utility.execute()
File "C:\Users\Owner\.virtualenvs\p1pRKLs2\Lib\site-packages\django\core\management\__init__.py", line 436, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "C:\Users\Owner\.virtualenvs\p1pRKLs2\Lib\site-packages\django\core\management\base.py", line 413, in run_from_argv
self.execute(*args, **cmd_options)
File "C:\Users\Owner\.virtualenvs\p1pRKLs2\Lib\site-packages\django\core\management\base.py", line 459, in execute
output = self.handle(*args, **options)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\Owner\.virtualenvs\p1pRKLs2\Lib\site-packages\django\core\management\base.py", line 107, in wrapper
res = handle_func(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\Owner\.virtualenvs\p1pRKLs2\Lib\site-packages\django\core\management\commands\migrate.py", line 357, in handle
post_migrate_state = executor.migrate(
^^^^^^^^^^^^^^^^^
File "C:\Users\Owner\.virtualenvs\p1pRKLs2\Lib\site-packages\django\db\migrations\executor.py", line 135, in migrate
state = self._migrate_all_forwards(
^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\Owner\.virtualenvs\p1pRKLs2\Lib\site-packages\django\db\migrations\executor.py", line 167, in _migrate_all_forwards
state = self.apply_migration(
^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\Owner\.virtualenvs\p1pRKLs2\Lib\site-packages\django\db\migrations\executor.py", line 255, in apply_migration
state = migration.apply(state, schema_editor)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\Owner\.virtualenvs\p1pRKLs2\Lib\site-packages\django\db\migrations\migration.py", line 132, in apply
operation.database_forwards(
File "C:\Users\Owner\.virtualenvs\p1pRKLs2\Lib\site-packages\django\db\migrations\operations\fields.py", line 110, in database_forwards
schema_editor.add_field(
File "C:\Users\Owner\.virtualenvs\p1pRKLs2\Lib\site-packages\django\db\backends\base\schema.py", line 722, in add_field
definition, params = self.column_sql(model, field, include_default=True)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\Owner\.virtualenvs\p1pRKLs2\Lib\site-packages\django\db\backends\base\schema.py", line 383, in column_sql
" ".join(
File "C:\Users\Owner\.virtualenvs\p1pRKLs2\Lib\site-packages\django\db\backends\base\schema.py", line 350, in _iter_column_sql
generated_sql, generated_params = self._column_generated_sql(field)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\Owner\.virtualenvs\p1pRKLs2\Lib\site-packages\django\db\backends\base\schema.py", line 448, in _column_generated_sql
expression_sql, params = field.generated_sql(self.connection)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\Owner\.virtualenvs\p1pRKLs2\Lib\site-packages\django\db\models\fields\generated.py", line 58, in generated_sql
resolved_expression = self.expression.resolve_expression(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\Owner\.virtualenvs\p1pRKLs2\Lib\site-packages\django\db\models\expressions.py", line 1629, in resolve_expression
c.cases[pos] = case.resolve_expression(
^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\Owner\.virtualenvs\p1pRKLs2\Lib\site-packages\django\db\models\expressions.py", line 1548, in resolve_expression
c.condition = c.condition.resolve_expression(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\Owner\.virtualenvs\p1pRKLs2\Lib\site-packages\django\db\models\query_utils.py", line 90, in resolve_expression
clause, joins = query._add_q(
^^^^^^^^^^^^^
File "C:\Users\Owner\.virtualenvs\p1pRKLs2\Lib\site-packages\django\db\models\sql\query.py", line 1641, in _add_q
child_clause, needed_inner = self.build_filter(
^^^^^^^^^^^^^^^^^^
File "C:\Users\Owner\.virtualenvs\p1pRKLs2\Lib\site-packages\django\db\models\sql\query.py", line 1488, in build_filter
arg, value = filter_expr
^^^^^^^^^^
ValueError: too many values to unpack (expected 2)
I've tried to manually edit the migration file so that it doesn't contain nested tuples, but this produced the same error:
condition=models.Q(
[
models.Q("media__endswith", "png"),
models.Q("media__endswith", "jpg"),
models.Q("media__endswith", "jpeg"),
models.Q("media__endswith", "gif"),
models.Q("media__endswith", "webp"),
],
"OR",
),
While I know that this is possible to achieve my desired result through post_save signals, it becomes pretty messy pretty quickly imho.
TYIA!
The condition is not constructed correctly, it should be:
class CampMedia(models.Model):
media = models.FileField(upload_to='camps')
is_image = models.GeneratedField(
expression=Case(
When(
condition=Q(
*[
Q(media__endswith=ext)
for ext in settings.VALID_IMAGE_FILETYPES
],
_connector=Q.OR
),
then=True,
),
default=False,
),
output_field=models.BooleanField(),
db_persist=True,
)