#25752: RenameField on m2m causes error when new m2m field is added with old 
name
-----------------------------+---------------------------------------------
     Reporter:  skyjur       |      Owner:  nobody
         Type:               |     Status:  new
  Uncategorized              |
    Component:  Migrations   |    Version:  1.8
     Severity:  Normal       |   Keywords:  postgres migrations renamefield
 Triage Stage:  Unreviewed   |  Has patch:  0
Easy pickings:  0            |      UI/UX:  0
-----------------------------+---------------------------------------------
 When in migrations I do RenameField on ManyToMany field, and then do
 AddField with ManyToMany with same name but different model, I get
 Integrity Error referring to existing index.

 It seems the problem is that RenameField does not rename database indexes,
 and then when new m2m field is being added it tries to create index with
 same name and so I get database error:

 {{{
 ...
   File "django/db/backends/utils.py", line 64, in execute
     return self.cursor.execute(sql, params)
   File "django/db/utils.py", line 97, in __exit__
     six.reraise(dj_exc_type, dj_exc_value, traceback)
   File "django/db/backends/utils.py", line 64, in execute
     return self.cursor.execute(sql, params)
 django.db.utils.ProgrammingError: relation "cms_test_many_2e06cda4"
 already exists
 }}}

 Here is how migration which creates this error looks like:

 {{{
 class Migration(migrations.Migration):

     dependencies = [
     ]

     operations = [
         migrations.RenameField(
             'test',
             'many',
             'many_legacy',
         ),
         migrations.AddField(
             model_name='test',
             name='many',
             field=models.ManyToManyField(to='cms.NewRel2'),
         ),
     ]

 }}}

 Initially I noticed this error on 1.7, then I also managed to replicate it
 on 1.8

 Error happened on postgres database.

--
Ticket URL: <https://code.djangoproject.com/ticket/25752>
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