The `ChangeList` does not support custom queryset subclasses

[jbronn]

Custom QuerySet classes (like GeoDjango's GeoQuerySet) ​can't be merged with regular QuerySet objects (using |, & operators). This problem manifests itself when trying to use search fields with a model that uses a QuerySet subclass:

TypeError ...
Cannot merge querysets of different types ('GeoQuerySet' and 'QuerySet'.

The root cause is that ChangeList ​hard-codes using QuerySet for the search fields.

In my patch ChangeList takes advantage of existing information to determine the type of queryset being used and store it in a root_query_set_class attribute that is used when performing searches.

[jbronn]

Allows for custom querysets in the admin changelist.

[Brian Rosner]

This looks right to me, but I think this should be applied to trunk first and then merged over to newforms-admin since this code isn't being directly modified in newforms-admin. Otherwise I'd apply this.

[Malcolm Tredinnick]

I think you're fixing the symptom, rather than the root problem, with this patch. The problem with the fix here is that it's only the tip of the iceberg. Every single reusable app that uses a QuerySet will have to write similarly awkward code.

The real issue is the tighter restrictions on QuerySet combinations, which has gone a little overboard. The idea behind that change was to prevent people doing silly things like trying to merge a QuerySet and a ValuesQuerySet (which I saw attempted in a post to django-users), not to prevent sensible merges. I didn't think of all the consequences at the time.The problem with the fix here is that it's only the tip of the iceberg. Every single reusable app that uses a QuerySet will have to write similarly awkward code.

I'll rethink the sanity check and possibly remove it entirely (leading to more "GIGO" behaviour) if there's nothing better.

[Malcolm Tredinnick]

Fixed in [7742] (by removing the overly-strict error checking).