id summary reporter owner description type status component version severity resolution keywords cc stage has_patch needs_docs needs_tests needs_better_patch easy ui_ux 35469 Squashing migrations from unique=True to unique=False to UniqueConstraint produces irreversible migration Jacob Walls nobody "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 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" Bug new Migrations 4.2 Normal Unreviewed 0 0 0 0 0 0