def _geo_field(self, field_name=None):
"""
Returns the first Geometry field encountered or the one specified via
the `field_name` keyword. The `field_name` may be a string specifying
the geometry field on this GeoQuerySet's model, or a lookup string
to a geometry field via a ForeignKey relation.
"""
if field_name is None:
# Incrementing until the first geographic field is found.
for field in self.model._meta.fields:
if isinstance(field, GeometryField):
return field
return False
else:
# Otherwise, check by the given field name -- which may be
# a lookup to a _related_ geographic field.
return GISLookup._check_geo_field(self.model._meta, field_name)
import warnings
