Question

I have a geographic object that is used in proximity searches. That object is keyed to different other objects via various paths.

Examples:

  blog.geo_object
  user.profile.geo_object
  group.event.geo_object

Right now, i do a bounding box search, which strings like this:

radius_queryset = base_queryset.filter(
    user__profile__geo__lat__gte = bounding_box.lat_min,
    user__profile__geo__lat__lte = bounding_box.lat_max,
    user__profile__geo__lon__gte = bounding_box.lon_min,
    user__profile__geo__lon__lte = bounding_box.lon_max,

and then on other objects:

radius_queryset = base_queryset.filter(
    blog__geo__lat__gte = bounding_box.lat_min,
    blog__geo__lat__lte = bounding_box.lat_max,
    blog__geo__lon__gte = bounding_box.lon_min,
    blog__geo__lon__lte = bounding_box.lon_max,
)

This follows a general format of:

radius_queryset = base_queryset.filter(
    [lookup_path]__geo__lat__gte = bounding_box.lat_min,
    [lookup_path]__geo__lat__lte = bounding_box.lat_max,
    [lookup_path]__geo__lon__gte = bounding_box.lon_min,
    [lookup_path]__geo__lon__lte = bounding_box.lon_max,
)
# where lookup_path = "blog"  or "user__profile" in the two above examples

I’m writing enough of these (3 so far, more to come) to want to generalize the queries — encapsulation being a good friend of maintainability and an ally in the fight against typo-bugs.

So, to my question: short of using exec and eval (which just look ugly), is there a way to get the filter parameter name to sub-in a variable? Am I missing something simple here?

Answer 1

**kwargs is your answer!

def generate_qs(lookup_path, bounding_box):
    return base_queryset.filter(**{
        lookup_path + '__geo__lat__gte' : bounding_box.lat_min,
        lookup_path + '__geo__lat__lte' : bounding_box.lat_max,
        lookup_path + '__geo__lon__gte' : bounding_box.lon_min,
        lookup_path + '__geo__lon__lte' : bounding_box.lon_max,
    })

radius_queryset = generate_qs('blog', bounding_box)