GeoDjango Distance() Annotation on Related Model

问题

I have a Profile class which is a OneToOne with Location model. Every profile has one and only location.

class Location(models.Model):
    profile = models.OneToOne(Profile)
    point = PointField()

In one of my views, I display a list of profiles. For example, I first find profiles with locations and then find associated profiles.

ref_location = Point(0,0) # point to calculate distances from
locations = Location.objects.filter(point__distance_lte=(ref_location, D(m=50 * 1000))) \
profiles = Profile.objects.filter(pk__in=locations.values('profile_id'))

What I would want is to be able to know the distance to each of these profile instances, e.g. I want to do something like:

profiles = Profile.objects.filter(pk__in=locations.values('profile_id'))\
.annotate(distance=Distance('location__point', ref_location))

and then iterate over

for p in profiles:
    print(p.distance.km)

Which is not possible

What I can do is annotate the locations instead, which isn't much use, because in the template I loop over profiles, not locations

回答1:

You can use Subquery (for Django version >= 1.11) to compose this query:

locations = Location.objects.filter(
    point__distance_lte=(OuterRef('ref_location'), D(m=50 * 1000))
).annotate(distance=Distance(OuterRef('point'), ref_location))

profiles = Profile.objects.filter(
    pk__in=Subquery(locations.values('profile_id')
).annotate(distance=Subquery(locations.values('distance')))

Or for Django version < 1.11 you can compose this query as follows:

locations = Location.objects.filter(
    point__distance_lte=(ref_location), D(m=50 * 1000))
).annotate(distance=Distance('point', ref_location))

profiles = Profile.objects.filter(
    pk__in=locations.values('profile_id')
).annotate(distance=locations.values('distance'))

The point is that you annotate the distance to the Location objects and then you annotate that distance to the appropriate profile.

来源：https://stackoverflow.com/questions/51506916/geodjango-distance-annotation-on-related-model

标签

python

django

geodjango