#35469: Squashing migrations from unique=True to unique=False to
UniqueConstraint
produces irreversible migration
-----------------------------+--------------------------------------
Reporter: Jacob Walls | Owner: nobody
Type: Bug | Status: new
Component: Migrations | Version: 4.2
Severity: Normal | Resolution:
Keywords: | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-----------------------------+--------------------------------------
Description changed by Jacob Walls:
Old description:
> Rhymes a bit with #31503, just in the reverse direction.
>
> - Create a model with a `unique=True` field, create a migration. I used
> URLField.
> - Create an empty migration, e.g with `migrations.RunSQL(sql="SELECT 1",
> reverse_sql="")`. (This will prevent the next AlterField from optimizing
> out when squashing. There are likely other possible reproducers without
> this step.)
> - Alter the field from step 1 to have `unique=False`, create a migration
> - Add a UniqueConstraint to the model that involves just that field,
> create a migration
> - Squash the four migrations
> - Migrate forward
> - Migrate to zero, with or without removing the other migrations or the
> `replaced` attribute
>
> Result:
> {{{
> Unapplying
> polls.0001_initial_squashed_0004_menu_unique_site...Traceback (most
> recent call last):
> File "/Users/jwalls/release/lib/python3.12/site-
> packages/django/db/backends/utils.py", line 87, in _execute
> return self.cursor.execute(sql)
> ^^^^^^^^^^^^^^^^^^^^^^^^
> psycopg2.errors.DuplicateTable: relation "polls_menu_site_61d71486_like"
> already exists
>
> The above exception was the direct cause of the following exception:
>
> Traceback (most recent call last):
> File "/Users/jwalls/prj/night/manage.py", line 22, in <module>
> main()
> File "/Users/jwalls/prj/night/manage.py", line 18, in main
> execute_from_command_line(sys.argv)
> File "/Users/jwalls/release/lib/python3.12/site-
> packages/django/core/management/__init__.py", line 442, in
> execute_from_command_line
> utility.execute()
> File "/Users/jwalls/release/lib/python3.12/site-
> packages/django/core/management/__init__.py", line 436, in execute
> self.fetch_command(subcommand).run_from_argv(self.argv)
> File "/Users/jwalls/release/lib/python3.12/site-
> packages/django/core/management/base.py", line 412, in run_from_argv
> self.execute(*args, **cmd_options)
> File "/Users/jwalls/release/lib/python3.12/site-
> packages/django/core/management/base.py", line 458, in execute
> output = self.handle(*args, **options)
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> File "/Users/jwalls/release/lib/python3.12/site-
> packages/django/core/management/base.py", line 106, in wrapper
> res = handle_func(*args, **kwargs)
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> File "/Users/jwalls/release/lib/python3.12/site-
> packages/django/core/management/commands/migrate.py", line 356, in handle
> post_migrate_state = executor.migrate(
> ^^^^^^^^^^^^^^^^^
> File "/Users/jwalls/release/lib/python3.12/site-
> packages/django/db/migrations/executor.py", line 141, in migrate
> state = self._migrate_all_backwards(plan, full_plan, fake=fake)
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> File "/Users/jwalls/release/lib/python3.12/site-
> packages/django/db/migrations/executor.py", line 219, in
> _migrate_all_backwards
> self.unapply_migration(states[migration], migration, fake=fake)
> File "/Users/jwalls/release/lib/python3.12/site-
> packages/django/db/migrations/executor.py", line 279, in
> unapply_migration
> state = migration.unapply(state, schema_editor)
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> File "/Users/jwalls/release/lib/python3.12/site-
> packages/django/db/migrations/migration.py", line 193, in unapply
> operation.database_backwards(
> File "/Users/jwalls/release/lib/python3.12/site-
> packages/django/db/migrations/operations/fields.py", line 240, in
> database_backwards
> self.database_forwards(app_label, schema_editor, from_state,
> to_state)
> File "/Users/jwalls/release/lib/python3.12/site-
> packages/django/db/migrations/operations/fields.py", line 235, in
> database_forwards
> schema_editor.alter_field(from_model, from_field, to_field)
> File "/Users/jwalls/release/lib/python3.12/site-
> packages/django/db/backends/base/schema.py", line 831, in alter_field
> self._alter_field(
> File "/Users/jwalls/release/lib/python3.12/site-
> packages/django/db/backends/postgresql/schema.py", line 304, in
> _alter_field
> self.execute(like_index_statement)
> File "/Users/jwalls/release/lib/python3.12/site-
> packages/django/db/backends/postgresql/schema.py", line 48, in execute
> return super().execute(sql, None)
> ^^^^^^^^^^^^^^^^^^^^^^^^^^
> File "/Users/jwalls/release/lib/python3.12/site-
> packages/django/db/backends/base/schema.py", line 201, in execute
> cursor.execute(sql, params)
> File "/Users/jwalls/release/lib/python3.12/site-
> packages/django/db/backends/utils.py", line 102, in execute
> return super().execute(sql, params)
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> File "/Users/jwalls/release/lib/python3.12/site-
> packages/django/db/backends/utils.py", line 67, in execute
> return self._execute_with_wrappers(
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> File "/Users/jwalls/release/lib/python3.12/site-
> packages/django/db/backends/utils.py", line 80, in _execute_with_wrappers
> return executor(sql, params, many, context)
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> File "/Users/jwalls/release/lib/python3.12/site-
> packages/django/db/backends/utils.py", line 84, in _execute
> with self.db.wrap_database_errors:
> File "/Users/jwalls/release/lib/python3.12/site-
> packages/django/db/utils.py", line 91, in __exit__
> raise dj_exc_value.with_traceback(traceback) from exc_value
> File "/Users/jwalls/release/lib/python3.12/site-
> packages/django/db/backends/utils.py", line 87, in _execute
> return self.cursor.execute(sql)
> ^^^^^^^^^^^^^^^^^^^^^^^^
> django.db.utils.ProgrammingError: relation
> "polls_menu_site_61d71486_like" already exists
> }}}
>
> ***
> failing squashed migration:
> {{{
> # Generated by Django 4.2.13 on 2024-05-21 00:59
>
> from django.db import migrations, models
>
> class Migration(migrations.Migration):
>
> dependencies = []
>
> operations = [
> migrations.CreateModel(
> name="Menu",
> fields=[
> (
> "id",
> models.BigAutoField(
> auto_created=True,
> primary_key=True,
> serialize=False,
> verbose_name="ID",
> ),
> ),
> ("site", models.URLField(unique=True)),
> ],
> ),
> migrations.RunSQL(
> sql="SELECT 1",
> reverse_sql="",
> ),
> migrations.AlterField(
> model_name="menu",
> name="site",
> field=models.URLField(),
> ),
> migrations.AddConstraint(
> model_name="menu",
> constraint=models.UniqueConstraint(models.F("site"),
> name="unique_site"),
> ),
> ]
> }}}
>
> My final model looked like:
> {{{
> from django.db import models
>
> class Menu(models.Model):
> site = models.URLField()
>
> class Meta:
> constraints = [
> models.UniqueConstraint(fields=["site"], name="unique_site")
> ]
> }}}
>
> Tested on postgres 14.3.2
New description:
Rhymes a bit with #31503, just in the reverse direction.
- Create a model with a `unique=True` field, create a migration. I used
URLField.
- Create an empty migration, e.g with `migrations.RunSQL(sql="SELECT 1",
reverse_sql="")`. (This will prevent the next AlterField from optimizing
out when squashing. There are likely other possible reproducers without
this step.)
- Alter the field from step 1 to have `unique=False`, create a migration
- Add a UniqueConstraint to the model that involves just that field,
create a migration
- Squash the four migrations
- Migrate forward
- Migrate to zero, with or without removing the other migrations or the
`replaced` attribute
Result:
{{{
Unapplying polls.0001_initial_squashed_0004_menu_unique_site...Traceback
(most recent call last):
File "/Users/jwalls/release/lib/python3.12/site-
packages/django/db/backends/utils.py", line 87, in _execute
return self.cursor.execute(sql)
^^^^^^^^^^^^^^^^^^^^^^^^
psycopg2.errors.DuplicateTable: relation "polls_menu_site_61d71486_like"
already exists
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "/Users/jwalls/prj/night/manage.py", line 22, in <module>
main()
File "/Users/jwalls/prj/night/manage.py", line 18, in main
execute_from_command_line(sys.argv)
File "/Users/jwalls/release/lib/python3.12/site-
packages/django/core/management/__init__.py", line 442, in
execute_from_command_line
utility.execute()
File "/Users/jwalls/release/lib/python3.12/site-
packages/django/core/management/__init__.py", line 436, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "/Users/jwalls/release/lib/python3.12/site-
packages/django/core/management/base.py", line 412, in run_from_argv
self.execute(*args, **cmd_options)
File "/Users/jwalls/release/lib/python3.12/site-
packages/django/core/management/base.py", line 458, in execute
output = self.handle(*args, **options)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/jwalls/release/lib/python3.12/site-
packages/django/core/management/base.py", line 106, in wrapper
res = handle_func(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/jwalls/release/lib/python3.12/site-
packages/django/core/management/commands/migrate.py", line 356, in handle
post_migrate_state = executor.migrate(
^^^^^^^^^^^^^^^^^
File "/Users/jwalls/release/lib/python3.12/site-
packages/django/db/migrations/executor.py", line 141, in migrate
state = self._migrate_all_backwards(plan, full_plan, fake=fake)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/jwalls/release/lib/python3.12/site-
packages/django/db/migrations/executor.py", line 219, in
_migrate_all_backwards
self.unapply_migration(states[migration], migration, fake=fake)
File "/Users/jwalls/release/lib/python3.12/site-
packages/django/db/migrations/executor.py", line 279, in unapply_migration
state = migration.unapply(state, schema_editor)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/jwalls/release/lib/python3.12/site-
packages/django/db/migrations/migration.py", line 193, in unapply
operation.database_backwards(
File "/Users/jwalls/release/lib/python3.12/site-
packages/django/db/migrations/operations/fields.py", line 240, in
database_backwards
self.database_forwards(app_label, schema_editor, from_state, to_state)
File "/Users/jwalls/release/lib/python3.12/site-
packages/django/db/migrations/operations/fields.py", line 235, in
database_forwards
schema_editor.alter_field(from_model, from_field, to_field)
File "/Users/jwalls/release/lib/python3.12/site-
packages/django/db/backends/base/schema.py", line 831, in alter_field
self._alter_field(
File "/Users/jwalls/release/lib/python3.12/site-
packages/django/db/backends/postgresql/schema.py", line 304, in
_alter_field
self.execute(like_index_statement)
File "/Users/jwalls/release/lib/python3.12/site-
packages/django/db/backends/postgresql/schema.py", line 48, in execute
return super().execute(sql, None)
^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/jwalls/release/lib/python3.12/site-
packages/django/db/backends/base/schema.py", line 201, in execute
cursor.execute(sql, params)
File "/Users/jwalls/release/lib/python3.12/site-
packages/django/db/backends/utils.py", line 102, in execute
return super().execute(sql, params)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/jwalls/release/lib/python3.12/site-
packages/django/db/backends/utils.py", line 67, in execute
return self._execute_with_wrappers(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/jwalls/release/lib/python3.12/site-
packages/django/db/backends/utils.py", line 80, in _execute_with_wrappers
return executor(sql, params, many, context)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/jwalls/release/lib/python3.12/site-
packages/django/db/backends/utils.py", line 84, in _execute
with self.db.wrap_database_errors:
File "/Users/jwalls/release/lib/python3.12/site-
packages/django/db/utils.py", line 91, in __exit__
raise dj_exc_value.with_traceback(traceback) from exc_value
File "/Users/jwalls/release/lib/python3.12/site-
packages/django/db/backends/utils.py", line 87, in _execute
return self.cursor.execute(sql)
^^^^^^^^^^^^^^^^^^^^^^^^
django.db.utils.ProgrammingError: relation "polls_menu_site_61d71486_like"
already exists
}}}
***
failing squashed migration:
{{{
# Generated by Django 4.2.13 on 2024-05-21 00:59
from django.db import migrations, models
class Migration(migrations.Migration):
dependencies = []
operations = [
migrations.CreateModel(
name="Menu",
fields=[
(
"id",
models.BigAutoField(
auto_created=True,
primary_key=True,
serialize=False,
verbose_name="ID",
),
),
("site", models.URLField(unique=True)),
],
),
migrations.RunSQL(
sql="SELECT 1",
reverse_sql="",
),
migrations.AlterField(
model_name="menu",
name="site",
field=models.URLField(),
),
migrations.AddConstraint(
model_name="menu",
constraint=models.UniqueConstraint(fields=("site",),
name="unique_site"),
),
]
}}}
My final model looked like:
{{{
from django.db import models
class Menu(models.Model):
site = models.URLField()
class Meta:
constraints = [
models.UniqueConstraint(fields=["site"], name="unique_site")
]
}}}
Tested on postgres 14.3.2
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Ticket URL: <https://code.djangoproject.com/ticket/35469#comment:1>
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