I have an album track model with a pre-defined Meta.ordering. In my debugger, I got bitten by something like this :
pdb> album.tracks.all()[0]
<Track: track 2>
ipdb> album.tracks.all() # WTF ?
[<Track: track 1>, <Track: track 2>]
ipdb> m = album.tracks.all()
ipdb> m[0]
<Track: track 2>
ipdb> m = list(album.tracks.all())
ipdb> m[0]
<Track: track 1>
Why does this happen ? Is there some best practices about this ?
Don't think the query set is ordered by default. Although it doesn't seem to be mentioned explicitly in the doc, but this can give some hint
On ordering and order_by()
Warning :
Ordering is not a free operation. Each field you add to the ordering incurs a cost to your database. Each foreign key you add will implicitly include all of its default orderings as well.
So if you have not specified any default ordering field, the queryset will not be ordered.
Sample:
>>> from myapp.models import *
>>> a=MyModel.objects.all()
>>> a.ordered
False
>>> b=MyModel.objects.all().order_by()
>>> b.ordered
False
>>> c=MyModel.objects.all().order_by('id')
>>> c.ordered
True
ordering for tracks? In my test I do get ordered==True when its set in Meta, even for ForeignKey relations (like user1.mymodel_set.all()).through model, and I should use order_with_respect_to