Fixed #27962 -- Allowed lookups on Area annotations.

django/contrib/gis/db/models/sql/conversion.py

@@ -7,6 +7,7 @@
 from django.contrib.gis.db.models.fields import GeoSelectFormatMixin
 from django.contrib.gis.geometry.backend import Geometry
 from django.contrib.gis.measure import Area, Distance
+from django.db import models
 
 
 class BaseField:
@@ -19,11 +20,21 @@ def select_format(self, compiler, sql, params):
         return sql, params
 
 
-class AreaField(BaseField):
+class AreaField(models.FloatField):
     "Wrapper for Area values."
     def __init__(self, area_att=None):
         self.area_att = area_att
 
+    def get_prep_value(self, value):
+        if not isinstance(value, Area):
+            raise ValueError('AreaField only accepts Area measurement objects.')
+        return value
+
+    def get_db_prep_value(self, value, connection, prepared=False):
+        if value is None or not self.area_att:
+            return value
+        return getattr(value, self.area_att)
+
     def from_db_value(self, value, expression, connection, context):
         if connection.features.interprets_empty_strings_as_nulls and value == '':
             value = None

tests/gis_tests/geoapp/test_functions.py

@@ -264,6 +264,19 @@ def test_area_with_regular_aggregate(self):
                 result = result.sq_m
             self.assertAlmostEqual((result - c.mpoly.area) / c.mpoly.area, 0)
 
+    @skipUnlessDBFeature("has_Area_function")
+    def test_area_lookups(self):
+        # Create projected country objects for the test to work on all backends.
+        CountryWebMercator.objects.bulk_create(
+            CountryWebMercator(name=c.name, mpoly=c.mpoly.transform(3857, clone=True))
+            for c in Country.objects.all()
+        )
+        qs = CountryWebMercator.objects.annotate(area=functions.Area('mpoly'))
+        self.assertEqual(qs.get(area__lt=Area(sq_km=500000)), CountryWebMercator.objects.get(name='New Zealand'))
+
+        with self.assertRaisesMessage(ValueError, 'AreaField only accepts Area measurement objects.'):
+            qs.get(area__lt=500000)
+
     @skipUnlessDBFeature("has_MakeValid_function")
     def test_make_valid(self):
         invalid_geom = fromstr('POLYGON((0 0, 0 1, 1 1, 1 0, 1 1, 1 0, 0 0))')