Django - can't delete rows when migrating backwards - django

Question

I have a problem. I implemented a migration to create another option on my model (add the preview textchoice) and implemented a RunPython method to create rows on a table that matches my requirements. This works.
The part that doesn't work is the reverse code. I simply query and filter the instances that I want to delete and try to delete them. In doing so, I get this weird error:
Unapplying applications.0012_alter_mediatype_name...Traceback (most recent call last):
File "/usr/local/lib/python3.10/runpy.py", line 196, in _run_module_as_main
return _run_code(code, main_globals, None,
File "/usr/local/lib/python3.10/runpy.py", line 86, in _run_code
exec(code, run_globals)
File "/root/.vscode-server/extensions/ms-python.python-2022.20.2/pythonFiles/lib/python/debugpy/adapter/../../debugpy/launcher/../../debugpy/__main__.py", line 39, in <module>
cli.main()
File "/root/.vscode-server/extensions/ms-python.python-2022.20.2/pythonFiles/lib/python/debugpy/adapter/../../debugpy/launcher/../../debugpy/../debugpy/server/cli.py", line 430, in main
run()
File "/root/.vscode-server/extensions/ms-python.python-2022.20.2/pythonFiles/lib/python/debugpy/adapter/../../debugpy/launcher/../../debugpy/../debugpy/server/cli.py", line 284, in run_file
runpy.run_path(target, run_name="__main__")
File "/root/.vscode-server/extensions/ms-python.python-2022.20.2/pythonFiles/lib/python/debugpy/_vendored/pydevd/_pydevd_bundle/pydevd_runpy.py", line 321, in run_path
return _run_module_code(code, init_globals, run_name,
File "/root/.vscode-server/extensions/ms-python.python-2022.20.2/pythonFiles/lib/python/debugpy/_vendored/pydevd/_pydevd_bundle/pydevd_runpy.py", line 135, in _run_module_code
_run_code(code, mod_globals, init_globals,
File "/root/.vscode-server/extensions/ms-python.python-2022.20.2/pythonFiles/lib/python/debugpy/_vendored/pydevd/_pydevd_bundle/pydevd_runpy.py", line 124, in _run_code
exec(code, run_globals)
File "/code/ews/manage.py", line 22, in <module>
main()
File "/code/ews/manage.py", line 18, in main
execute_from_command_line(sys.argv)
File "/usr/local/lib/python3.10/site-packages/django/core/management/__init__.py", line 446, in execute_from_command_line
utility.execute()
File "/usr/local/lib/python3.10/site-packages/django/core/management/__init__.py", line 440, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "/usr/local/lib/python3.10/site-packages/django/core/management/base.py", line 414, in run_from_argv
self.execute(*args, **cmd_options)
File "/usr/local/lib/python3.10/site-packages/django/core/management/base.py", line 460, in execute
output = self.handle(*args, **options)
File "/usr/local/lib/python3.10/site-packages/django/core/management/base.py", line 98, in wrapped
res = handle_func(*args, **kwargs)
File "/usr/local/lib/python3.10/site-packages/django/core/management/commands/migrate.py", line 290, in handle
post_migrate_state = executor.migrate(
File "/usr/local/lib/python3.10/site-packages/django/db/migrations/executor.py", line 137, in migrate
state = self._migrate_all_backwards(plan, full_plan, fake=fake)
File "/usr/local/lib/python3.10/site-packages/django/db/migrations/executor.py", line 215, in _migrate_all_backwards
self.unapply_migration(states[migration], migration, fake=fake)
File "/usr/local/lib/python3.10/site-packages/django/db/migrations/executor.py", line 275, in unapply_migration
state = migration.unapply(state, schema_editor)
File "/usr/local/lib/python3.10/site-packages/django/db/migrations/migration.py", line 191, in unapply
operation.database_backwards(
File "/usr/local/lib/python3.10/site-packages/django/db/migrations/operations/special.py", line 201, in database_backwards
self.reverse_code(from_state.apps, schema_editor)
File "/code/ews/applications/migrations/0012_alter_mediatype_name.py", line 45, in reverter
).delete()
File "/usr/local/lib/python3.10/site-packages/django/db/models/query.py", line 826, in delete
collector.collect(del_query)
File "/usr/local/lib/python3.10/site-packages/django/db/models/deletion.py", line 343, in collect
field.remote_field.on_delete(self, field, sub_objs, self.using)
File "/usr/local/lib/python3.10/site-packages/django/db/models/deletion.py", line 23, in CASCADE
collector.collect(
File "/usr/local/lib/python3.10/site-packages/django/db/models/deletion.py", line 321, in collect
sub_objs = self.related_objects(related_model, [field], batch)
File "/usr/local/lib/python3.10/site-packages/django/db/models/deletion.py", line 404, in related_objects
return related_model._base_manager.using(self.using).filter(predicate)
File "/usr/local/lib/python3.10/site-packages/django/db/models/query.py", line 1071, in filter
return self._filter_or_exclude(False, args, kwargs)
File "/usr/local/lib/python3.10/site-packages/django/db/models/query.py", line 1089, in _filter_or_exclude
clone._filter_or_exclude_inplace(negate, args, kwargs)
File "/usr/local/lib/python3.10/site-packages/django/db/models/query.py", line 1096, in _filter_or_exclude_inplace
self._query.add_q(Q(*args, **kwargs))
File "/usr/local/lib/python3.10/site-packages/django/db/models/sql/query.py", line 1502, in add_q
clause, _ = self._add_q(q_object, self.used_aliases)
File "/usr/local/lib/python3.10/site-packages/django/db/models/sql/query.py", line 1532, in _add_q
child_clause, needed_inner = self.build_filter(
File "/usr/local/lib/python3.10/site-packages/django/db/models/sql/query.py", line 1358, in build_filter
return self._add_q(
File "/usr/local/lib/python3.10/site-packages/django/db/models/sql/query.py", line 1532, in _add_q
child_clause, needed_inner = self.build_filter(
File "/usr/local/lib/python3.10/site-packages/django/db/models/sql/query.py", line 1415, in build_filter
self.check_related_objects(join_info.final_field, value, join_info.opts)
File "/usr/local/lib/python3.10/site-packages/django/db/models/sql/query.py", line 1229, in check_related_objects
self.check_query_object_type(v, opts, field)
File "/usr/local/lib/python3.10/site-packages/django/db/models/sql/query.py", line 1203, in check_query_object_type
raise ValueError(
ValueError: Cannot query "MediaSize object (0a803f4c-f9e0-4b2d-ae2a-c02d7b9e12b6)": Must be "MediaSize" instance.
This error does not make sense. Does anyone have a clue of what it can be?
The migration code:
from django.db import migrations, models
def converter(apps, schema_editor):
AppExtension = apps.get_model("applications", "AppExtension")
MediaType = apps.get_model("applications", "MediaType")
MediaSize = apps.get_model("applications", "MediaSize")
all_extensions = AppExtension.objects.all()
media_types = []
media_sizes = []
for extension in all_extensions:
mediatype_extension = MediaType(extension=extension, name="preview")
media_types.append(mediatype_extension)
media_sizes.append(
MediaSize(
media_type=mediatype_extension,
name="intrinsic",
width=1920,
height=960,
)
)
media_sizes.append(
MediaSize(
media_type=mediatype_extension,
name="optimized",
width=960,
height=480,
)
)
MediaType.objects.bulk_create(media_types)
MediaSize.objects.bulk_create(media_sizes)
def reverter(apps, schema_editor):
MediaType = apps.get_model("applications", "MediaType")
all_extensions = AppExtension.objects.all()
MediaType.objects.filter(
name="preview",
).delete()
class Migration(migrations.Migration):
dependencies = [
("applications", "0011_alter_mediatype_name"),
]
operations = [
migrations.AlterField(
model_name="mediatype",
name="name",
field=models.CharField(
choices=[
("thumbnail", "Thumbnail"),
("icon", "Icon"),
("app-icon", "App Icon"),
("preview", "Preview"),
],
default="thumbnail",
help_text="Name of this media type",
max_length=32,
verbose_name="Name",
),
),
migrations.RunPython(converter, reverse_code=reverter),
]
My models:
class MediaType(UUIDModel):
class TypeChoices(models.TextChoices):
THUMBNAIL = "thumbnail", "Thumbnail"
ICON = "icon", "Icon"
APP_ICON = "app-icon", "App Icon"
PREVIEW = "preview", "Preview"
extension = models.ForeignKey(
AppExtension,
on_delete=models.CASCADE,
related_name="media_types",
verbose_name=_("AppExtension"),
help_text="AppExtension this MediaType belongs to",
)
name = models.CharField(
max_length=32,
verbose_name=_("Name"),
help_text=f"Name of this media type",
choices=TypeChoices.choices,
default=TypeChoices.THUMBNAIL,
)
#property
def sizes_dict(self) -> dict:
if self.sizes.exist():
return {size.name: size.get_tuple() for size in self.sizes.all()}
return {}
def __str__(self) -> str:
return f"{self.extension.name} - {self.name}"
class Meta:
constraints = [
UniqueConstraint(
fields=["extension", "name"],
name="unique_media_type_name_per_extension",
),
]
class MediaSize(UUIDModel):
class SizeChoices(models.TextChoices):
INTRINSIC = "intrinsic", "Intrinsic"
OPTIMIZED = "optimized", "Optimized"
media_type = models.ForeignKey(
MediaType,
on_delete=models.CASCADE,
verbose_name=_("Media Type"),
help_text="Media type this size reffers to",
related_name="sizes",
)
name = models.CharField(
max_length=32,
verbose_name=_("Name"),
help_text=f"Name of this media size",
choices=SizeChoices.choices,
default=SizeChoices.INTRINSIC,
)
width = models.PositiveIntegerField(
verbose_name=_("Width"),
help_text="Width of this media size",
)
height = models.PositiveIntegerField(
verbose_name=_("Height"),
help_text="Height of this media size",
)
def get_tuple(self) -> Tuple[int, int]:
return self.width, self.height
def __str__(self) -> str:
return (
f"{self.media_type.extension.name} - {self.media_type.name}"
+ f" - {self.name}: ({self.get_tuple()})"
)
class Meta:
constraints = [
UniqueConstraint(
fields=["media_type", "name"],
name="unique_media_size_name_per_media_type",
),
UniqueConstraint(
fields=["media_type", "height", "width"],
name="unique_media_size_dimensions_per_media_type",
),
]
Tried to run the exact same code to delete the rows outside the migration -> it works
Tried to stop the migration in between, get a single instance of the nested MediaSize type and delete it -> raises same error
Running the migration with and without the vscode debugger raises the same error
It is possible to update and save the instance during the migration, just the delete operation raises this error.
Update:
Separating the AlterField and RunPython operations into two different migration files, and running those files separately works. Running both at once gives the same error.

Answer 1

Try to just remove reverse_code. I dont think you need it since the operation doesnt need to be reverted.