I am using django 0.96.1 mostly for its database API on a large project. I need to retrieve many-ended relationship data. For example, for every user, I need to know what groups they are in. As expected, there is a many-to-many relationship.
The code I've written will get a queryset of users filtered by some arbitrary
criteria, call the values() method, and then iterate over the results. For
each row, it calls a "getter" for the group relationship. That getter
receives a parameter current_user_id and does this:
group.objects.filter(user__id__exact = current_user_id).values('id')
It then converts the list of dictionaries into just a list of integers, and
returns the results. This way I am augmenting the user.objects.values()
result set with lists of foreign keys representing the many-end of a
relationship. I end up with results looking like this:
[{ 'username' : 'jshmoe', 'first_name' : 'Joe', 'last_name' : 'Shmoe', 'groups'
:
[ 3, 5, 6, 14] }]
The problem is that this is slow, I think because it's executing a new
database query for each user. It's even worse because many objects in my
data model have several many-ended relationships. Using 6 such getters on
1000 users is taking about 8 seconds to return, running on respectable
hardware.
Is there an appropriate django way to run only one query to retrieve all of
these results? I guess all I really need is the contents of the user_groups
table, filtered by some collection of user ids. Then I can do the matching
myself in code.
Thanks for your help,
Michael
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