[Python-modules-team] Bug#863267: Bug#863267: Bug#863267: Miscalculates MigrationHistory dependencies between multiple django apps - regression from 1.8

[Neil Williams]

On Fri, 26 May 2017 10:05:58 +0100
Neil Williams <codehelp at debian.org> wrote:

> On Fri, 26 May 2017 18:56:04 +1000
> Brian May <bam at debian.org> wrote:
> 
> > Neil Williams <codehelp at debian.org> writes:
> >   
> > > django.db.migrations.exceptions.InconsistentMigrationHistory:
> > > Migration lava_scheduler_app.0001_initial is applied before its
> > > dependency linaro_django_xmlrpc.0001_initial on database
> > > 'default'.    
> > 
> > Ok, I see what is going on now. Untested theory at the moment, but
> > it fits the symptoms.
> > 
> > ./lava_scheduler_app/migrations/0001_initial.py contains:
> > 
> >     dependencies = [  
> >         ('auth', '0001_initial'),  
> >         migrations.swappable_dependency(settings.AUTH_USER_MODEL),  
> >         ('linaro_django_xmlrpc', '__first__'),  
> >         ('dashboard_app', '__first__'),  
> >     ]    
> 
> Again, I also spotted this and thought it was the source. However,
> changing this causes the migration to fail with 1.10 as there are
> objects in this model which must be applied before
> lava_scheduler_app/0001_initial will complete. e.g. the AuthToken
> object is referred to directly in lava_scheduler_app/0001_initial and
> this is defined by linaro_django_xmlrpc
> 
> I tried a few simplistic edits of those migration files on a test
> instance, the migrations still fail to apply.
> 
> > 
> > My reading of this is that this means this migration depends on the
> > first migration from 'linaro_django_xmlrpc' to be already
> > applied. However on Jessie, 'linaro_django_xmlrpc' has no
> > migrations. Hence I suspect whatever version of Django that
> > installed this migration to be buggy, because it didn't check the
> > dependencies could be satisfied. Or maybe this was considered OK at
> > the time.  
> 
> 7/9 Add initial Django migrations
>     
>     From a25d49c6c96217011fead69b675e281b6e5b8fc5 Mon Sep 17 00:00:00
>     2001
>     From: Raphaël Hertzog <hertzog at debian.org> Date: Tue, 9 Sep
>     2014 07:20:56 +0000 
> 
> https://git.linaro.org/lava/lava-server.git/commit/?id=9e5595adae2b2ea6fc7e19820356ca1bd098110c
> 
> > This migration is already applied when we come to do the new
> > migrations for Django 1.8 or Django 1.10
> > 
> > Django 1.8 doesn't care that the first migration for
> > 'linaro_django_xmlrpc' hasn't been applied yet. As a result, it can
> > fake the migration and everyone is happy.
> > 
> > Django 1.10 does care. It says the database is broken because the
> > prerequisite for this migration was never applied. It does this
> > check before applying any migrations.
> > 
> > I don't know for sure what is correct behaviour here.  
> 
> Changing existing migration files *after* user data has been created
> is likely to cause data loss.
> 
> > However I am
> > inclined to think maybe this isn't a Django 1.10 fault, because the
> > migration in Jessie clearly says it depends on a migration that was
> > never applied - because it doesn't even exist at this point.  
> 
> No. This is django making the wrong decision about problems it has
> previously supported when trying to include bug fixes for other
> problems. It is a regression in django 1.10.
> 

Operations to perform:
  Synchronize unmigrated apps: linaro_django_xmlrpc, django_openid_auth, lava_projects, lava_scheduler_daemon, django_tables2, lava_markitup
  Apply all migrations: sessions, admin, dashboard_app, auth, sites, contenttypes, lava_scheduler_app, google_analytics
Synchronizing apps without migrations:
  Creating tables...
    Creating table django_openid_auth_nonce
    Creating table django_openid_auth_association
    Creating table django_openid_auth_useropenid
    Creating table linaro_django_xmlrpc_authtoken

From the installation of 2014.9-1 from jessie.

At no point did 1.7 require or support linaro_django_xmlrpc migrations.
(Creating them caused django to fail to apply them.) It's not that is
does not exist, it is that django 1.7 in jessie does not allow it to
exist - yet 1.10 requires it and it's code in 1.8 that handles the
transition.

-- 


Neil Williams
=============
http://www.linux.codehelp.co.uk/

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