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
26535	Possible bug - when migrating and removing unique constraint.	jenlu	nobody	"Possible bug - when migrating and removing unique constraint.

Postgres 9.4.1 / 9.5.7 + Django 1.9.5 + psycopg 2.6.1

——

My setup is models/database representing sports events, and with competitors in different events.

Each competitor in different sports has for their model/class:
{{{
   class Meta:
       unique_together = ('event', 'number')
}}}
i.e. ensure a unique starting number in an event, now we are relaxing (removing this constraint)
this but having issues when migrating.

The above is represented in postgress as a UNIQUE constraint
and in all models.py the above constraint is as-above — but in pg it is represented as

(i) UNIQUE (event_id, number)

and sometimes as...

(ii) UNIQUE (number, event_id)

…and now when doing migration - for all tables where it is represented as (i) everything
goes well, but in tables where (ii) the following error:
{{{
 File ""/Users/XXX/.virtualenvs/ssi195_2711/lib/python2.7/site-packages/django/db/migrations/migration.py"", line 123, in apply
   operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
 File ""/Users/XXX/.virtualenvs/ssi195_2711/lib/python2.7/site-packages/django/db/migrations/operations/models.py"", line 359, in database_forwards
   getattr(new_model._meta, self.option_name, set()),
 File ""/Users/XXX/.virtualenvs/ssi195_2711/lib/python2.7/site-packages/django/db/backends/base/schema.py"", line 318, in alter_unique_together
   self._delete_composed_index(model, fields, {'unique': True}, self.sql_delete_unique)
 File ""/Users/XXX/.virtualenvs/ssi195_2711/lib/python2.7/site-packages/django/db/backends/base/schema.py"", line 347, in _delete_composed_index
   "", "".join(columns),
ValueError: Found wrong number (0) of constraints for match_ppc_ppccompetitor(event_id, number)
}}}
So seems to need to do some migrations manually and no biggie - but yet strange and unsure if Django or pg issue….

/ Jens"	Uncategorized	new	Migrations	1.9	Normal				Unreviewed	0	0	0	0	0	0