Opened 17 months ago
Closed 17 months ago
#34647 closed Bug (duplicate)
Foreign Key index names are not renamed when a model is renamed causing duplicate key if a model with the origin name and column is added
Reported by: | Steven Mapes | Owned by: | nobody |
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Component: | Migrations | Version: | 4.2 |
Severity: | Normal | Keywords: | migrations, sql, foreign_key, mysql |
Cc: | Bhuvnesh, Simon Charette, Mariusz Felisiak, David, Wobrock | Triage Stage: | Unreviewed |
Has patch: | no | Needs documentation: | no |
Needs tests: | no | Patch needs improvement: | no |
Easy pickings: | no | UI/UX: | no |
Description (last modified by )
I encountered an issue yesterday where Django created a foreign key that already exists.
The way I encountered this was to take a model called CriticalPathTemplate
with a property called archived_by
which is a foreign key to the user table, then renamed the model to CriticalPathTemplateOld
and ran migrations. This renamed the table but left the indexes as they were.
I then added a new model called CriticalPathTemplate
, a business requirement, and ran makemigrations and migrate. The migrations were made but makemigrations failed due to a foreign key name clash. I ended up renaming the column but then hit further issues for the next FK in the table, there are a few.
Looking at the output of sqlmigrate for the new migration and comparing the name of the foreign keys that Django generated I can see several that are going to clash as the indexes on the old table were not renamed when the table was renamed by the migration.
Here's how to create the problem on a fresh project
from django.db import models from django.contrib.auth.models import User class ThisIsAModelWithALongName(models.Model): name = models.CharField(max_length=128, blank=True) archived_by = models.ForeignKey(User, null=True, blank=True, default=None, related_name="model_with_log_names", on_delete=models.SET_NULL) class AnotherClassHere(models.Model): long_name_property = models.ForeignKey(ThisIsAModelWithALongName, null=True, blank=True, default=None, related_name="another_class_here", on_delete=models.SET_NULL)
python manage.py makemigrations && python manage.py migrate
Step 2 - Rename the top class and the FK in the 2nd class but leave the related name in the first class
from django.db import models from django.contrib.auth.models import User class ThisIsAModelWithALongNameOld(models.Model): name = models.CharField(max_length=128, blank=True) archived_by = models.ForeignKey(User, null=True, blank=True, default=None, related_name="model_with_log_names", on_delete=models.SET_NULL) class AnotherClassHere(models.Model): long_name_property_old = models.ForeignKey(ThisIsAModelWithALongNameOld, null=True, blank=True, default=None, related_name="another_class_here", on_delete=models.SET_NULL)
Run migrations
Step 3 - Add the new model back, add an FK into the AnotherClassHere table and rename the related_name on the first (old) model
from django.db import models from django.contrib.auth.models import User class ThisIsAModelWithALongNameOld(models.Model): name = models.CharField(max_length=128, blank=True) archived_by = models.ForeignKey(User, null=True, blank=True, default=None, related_name="model_with_log_names_old", on_delete=models.SET_NULL) class ThisIsAModelWithALongName(models.Model): name = models.CharField(max_length=128, blank=True) archived_by = models.ForeignKey(User, null=True, blank=True, default=None, related_name="model_with_log_names", on_delete=models.SET_NULL) class AnotherClassHere(models.Model): long_name_property_old = models.ForeignKey(ThisIsAModelWithALongNameOld, null=True, blank=True, default=None, related_name="another_class_here", on_delete=models.SET_NULL) long_name_property = models.ForeignKey(ThisIsAModelWithALongName, null=True, blank=True, default=None, related_name="another_class_here", on_delete=models.SET_NULL)
run migrations, the error will occur and the DB will be left in a partially migrated state that can't be rolled back.
It's important to do this as a three step process and not to just jump from Step 1 to Step 2 as that will result in the table being dropped and recreated which will bypass the issue but you'd loose any data that was in the table.
It's the first time I've every had to rename a model then create a new class with the same name so I'm sure it's a rare occurrence. My work around at the moment will be to create the migration, run a sql migrate to capture the raw SQL, then edit the migration to stop it running and create a new empty migration that can run the raw SQL but after I manually edit all the FKs that are clashing
Change History (4)
comment:1 by , 17 months ago
Description: | modified (diff) |
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comment:2 by , 17 months ago
Description: | modified (diff) |
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Summary: | Foreign Key index names are not renamed when a model is renamed → Foreign Key index names are not renamed when a model is renamed causing duplicate key if a model with the origin name and column is added |
comment:3 by , 17 months ago
Cc: | added |
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I'm inclined to accept this ticket because:
django.db.utils.ProgrammingError: relation "ticket_34647_thisisamodelwithalongname_archived_by_id_63c0d1af" already exists
Adding as CC a few folks who I think would have a better understanding of the migrations logic in order to better triage this ticket.