Correctly calculate area (fixes #1689)

cadasta/organization/tests/test_downloads.py

@@ -475,15 +475,14 @@ def test_write_features(self):
                 if i == 2:
                     assert row == [su2.id, su2.type, '', 'linestring']
                 if i == 3:
-                    area = format(su3.area, '.2f')
-                    assert row == [su3.id, su3.type, area, 'polygon']
+                    assert row == [su3.id, su3.type, str(su3.area), 'polygon']
                 if i == 4:
                     assert row == [su4.id, su4.type, '', 'multipoint']
                 if i == 5:
-                    area = su5.area
                     assert row == [su5.id, su5.type, '', 'multilinestring']
                 if i == 6:
-                    assert row == [su6.id, su6.type, '', 'multipolygon']
+                    assert row == [su6.id, su6.type, str(su6.area),
+                                   'multipolygon']
                 if i == 7:
                     assert row == [su7.id, su7.type, '', 'empty']
                 if i == 8:

cadasta/spatial/managers.py

@@ -1,4 +1,3 @@
-from . import models as spatial_models
 from .exceptions import SpatialRelationshipError
 from party.managers import BaseRelationshipManager
 
@@ -11,25 +10,17 @@ def create(self, *args, **kwargs):
         su1 = kwargs['su1']
         su2 = kwargs['su2']
         project = kwargs['project']
-        if (su1.geometry is not None and
-                su2.geometry is not None):
-
-            if (kwargs['type'] == 'C' and
-                    su1.geometry.geom_type == 'Polygon'):
-                result = spatial_models.SpatialUnit.objects.filter(
-                    id=su1.id
-                ).filter(
-                    geometry__contains=su2.geometry
-                )
-
-                if len(result) != 0:
-                    self.check_project_constraints(
-                        project=project, left=su1, right=su2)
-                    return super().create(**kwargs)
-                else:
-                    raise SpatialRelationshipError(
-                        """That selected location is not geographically
-                        contained within the parent location""")
+        rel_error = (
+            kwargs['type'] == 'C' and
+            su1.geometry is not None and
+            su2.geometry is not None and
+            su1.geometry.geom_type == 'Polygon' and
+            not su1.geometry.contains(su2.geometry)
+        )
+        if rel_error:
+            raise SpatialRelationshipError(
+                "That selected location is not geographically "
+                "contained within the parent location")
         self.check_project_constraints(
             project=project, left=su1, right=su2)
         return super().create(**kwargs)

cadasta/spatial/migrations/0005_recalculate_area.py

@@ -0,0 +1,62 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.10.7 on 2017-08-03 17:18
+from __future__ import unicode_literals
+
+import django.contrib.gis.db.models.fields
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    TABLE_NAME = 'spatial_spatialunit'
+    FUNC_NAME = 'calculate_area'
+    TRIGGER_NAME = '{}_trigger'.format(FUNC_NAME)
+
+    dependencies = [
+        ('spatial', '0004_area_location_field'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='historicalspatialunit',
+            name='geometry',
+            field=django.contrib.gis.db.models.fields.GeometryField(geography=True, null=True, srid=4326),
+        ),
+        migrations.AlterField(
+            model_name='spatialunit',
+            name='geometry',
+            field=django.contrib.gis.db.models.fields.GeometryField(geography=True, null=True, srid=4326),
+        ),
+        migrations.RunSQL(
+            (
+                "UPDATE {table} SET area = ST_Area(geography(geometry)) "
+                "WHERE geometrytype(geometry) LIKE '%POLYGON';"
+            ).format(table=TABLE_NAME),
+            reverse_sql=migrations.RunSQL.noop
+        ),
+        migrations.RunSQL(
+            """
+            CREATE FUNCTION {func}() RETURNS trigger AS $$
+            BEGIN
+                IF geometrytype(NEW.geometry) LIKE '%POLYGON'
+                THEN
+                    NEW.area := (SELECT ST_Area(geography(NEW.geometry)));
+                ELSE
+                    NEW.area := null;
+                END IF;
+                RETURN NEW;
+            END;
+            $$ language plpgsql;
+
+            CREATE TRIGGER {trigger}
+                BEFORE INSERT OR UPDATE
+                ON {table}
+                FOR EACH ROW
+                EXECUTE PROCEDURE {func}();
+            """.format(func=FUNC_NAME, trigger=TRIGGER_NAME, table=TABLE_NAME),
+            reverse_sql="""
+                DROP TRIGGER {trigger} ON {table};
+                DROP FUNCTION {func}();
+            """.format(func=FUNC_NAME, trigger=TRIGGER_NAME, table=TABLE_NAME)
+        )
+    ]

cadasta/spatial/models.py

@@ -39,8 +39,9 @@ class SpatialUnit(ResourceModelMixin, RandomIDModel):
 
     # Spatial unit geometry is optional: some spatial units may only
     # have a textual description of their location.
-    geometry = GeometryField(null=True)
+    geometry = GeometryField(null=True, geography=True)
 
+    # Area, auto-calculated via trigger (see spatial/migrations/#0005)
     area = models.FloatField(null=True)
 
     # JSON attributes field with management of allowed members.
@@ -170,20 +171,22 @@ def check_extent(sender, instance, **kwargs):
     # (https://trac.osgeo.org/geos/ticket/680)
     # TODO: Rm this check when we're using Django 1.11+ or libgeos 3.6.1+
     # https://github.com/django/django/commit/b90d72facf1e4294df1c2e6b51b26f6879bf2992#diff-181a3ea304dfaf57f1e1d680b32d2b76R248
-    from django.contrib.gis.geos.polygon import Polygon
+    from django.contrib.gis.geos import Polygon
     if isinstance(geom, Polygon) and geom.empty:
         instance.geometry = None
-
     if geom and not geom.empty:
         reassign_spatial_geometry(instance)
 
 
-@receiver(models.signals.pre_save, sender=SpatialUnit)
-def calculate_area(sender, instance, **kwargs):
+@receiver(models.signals.post_save, sender=SpatialUnit)
+def refresh_area(sender, instance, **kwargs):
+    """ Ensure DB-generated area is set on instance """
+    from django.contrib.gis.geos import MultiPolygon, Polygon
     geom = instance.geometry
-    from django.contrib.gis.geos.polygon import Polygon
-    if geom and isinstance(geom, Polygon) and geom.valid:
-        instance.area = geom.transform(3857, clone=True).area
+    if not isinstance(geom, (MultiPolygon, Polygon)):
+        return
+    qs = type(instance)._default_manager.filter(id=instance.id)
+    instance.area = qs.values_list('area', flat=True)[0]
 
 
 @fix_model_for_attributes

cadasta/spatial/tests/test_models.py

@@ -184,7 +184,7 @@ def test_ui_class_name(self):
     def test_area(self):
         su = SpatialUnitFactory.create(geometry='SRID=4326;POLYGON \
             ((30 10, 20 20, 20 20, 10 20, 30 10))')
-        assert su.area == 642391915473.7279
+        assert su.area == 554923434497.9
 
     def test_area_no_geometry(self):
         su = SpatialUnitFactory.create()