admin app's change list usage of select related - maximum depth

What about a depth argument like implemented and documented at http://docs.djangoproject.com/en/dev/ref/models/querysets/#id4 ? (granted, perhaps it should be included in the signature in the section title)

I think maybe a better place to address this issue is in the admin application by just adding a depth=3 parameter to the two select_related instructions in admin/views/main.py

def get_query_set(self):
    ...

        # Use select_related() if one of the list_display options is a field
        # with a relationship.
        if self.list_select_related:
            qs = qs.select_related(depth=3)
        else:
            for field_name in self.list_display:
                try:
                    f = self.lookup_opts.get_field(field_name)
                except models.FieldDoesNotExist:
                    pass
                else:
                    if isinstance(f.rel, models.ManyToOneRel):
                        qs = qs.select_related(depth=3)
                        break

So, you were talking specifically about the admin contrib app?.

This doesn't sound like a clear problem description to me yet. Select_related already has a default maximum depth of 5, which already meets the definition of "sensible" for many cases. I don't see any great need to micromanage at that point by saying "perhaps 2 or 3 is better" -- we just pick a value and stick with it and 5 is the current value. We could be here all day debating 2 or 3 or 5 or 7.

So the real issue is why this particular problem report is not respecting the maximum depth of 5. If it is, then this becomes a proposal to change 5 to 3 and ... meh.

ramiro: yes, I only picked it up in the admin contrib app. At that stage I was unaware of the depth=X parameter. I think it adequately addresses the issue for custom applications, also I don't think internally select_related needs to drop the 5 down to 3.

BUT, for the admin application I think a tweak is required. Arguments for explicitly lowering select_related for admin to say 3 :) are;

1) Whatever value you take must hit the sweat spot for 90% of situations otherwise it will slow down rather than increase overall application speed. I can not even think of an example where I want to go down 5 levels. (object.level1.level2.level3.level4.level5)

2) Remember that the effect on the database increases exponentially, e.g.

3 levels 2 references per object => 3² = 9 DB tables

5 levels 2 references per object => 5² = 25 DB tables

5 levels 3 references per object => 5³ = 125 DB tables

#9849 (closed as a duplicate of this ticket) proposed being able to control the select related queries by being able to specify which relationships to follow.

Yeah, let's not micromanage the admin like this. You can just override queryset if you need advanced usage.