django1/django/contrib/gis/db/models/aggregates.py

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from django.db.models import Aggregate
from django.contrib.gis.db.backend import SpatialBackend
from django.contrib.gis.db.models.sql import GeomField
class GeoAggregate(Aggregate):
def add_to_query(self, query, alias, col, source, is_summary):
if hasattr(source, 'geom_type'):
# Doing additional setup on the Query object for spatial aggregates.
aggregate = getattr(query.aggregates_module, self.name)
# Adding a conversion class instance and any selection wrapping
# SQL (e.g., needed by Oracle).
if aggregate.conversion_class is GeomField:
query.extra_select_fields[alias] = GeomField()
if SpatialBackend.select:
query.custom_select[alias] = SpatialBackend.select
super(GeoAggregate, self).add_to_query(query, alias, col, source, is_summary)
class Collect(GeoAggregate):
name = 'Collect'
class Extent(GeoAggregate):
name = 'Extent'
class MakeLine(GeoAggregate):
name = 'MakeLine'
class Union(GeoAggregate):
name = 'Union'