Fixed #27576 -- Made get_srid_info() fallback to GDAL if SpatialRefSys is unavailable.

django/contrib/gis/db/models/fields.py

@@ -1,8 +1,11 @@
+from collections import defaultdict
+
 from django.contrib.gis import forms, gdal
 from django.contrib.gis.db.models.lookups import (
     RasterBandTransform, gis_lookups,
 )
 from django.contrib.gis.db.models.proxy import SpatialProxy
+from django.contrib.gis.gdal import SpatialReference
 from django.contrib.gis.gdal.error import GDALException
 from django.contrib.gis.geometry.backend import Geometry, GeometryException
 from django.core.exceptions import ImproperlyConfigured
@@ -14,7 +17,7 @@ from django.utils.translation import ugettext_lazy as _
 # Local cache of the spatial_ref_sys table, which holds SRID data for each
 # spatial database alias. This cache exists so that the database isn't queried
 # for SRID info each time a distance query is constructed.
-_srid_cache = {}
+_srid_cache = defaultdict(dict)
 
 
 def get_srid_info(srid, connection):
@@ -29,21 +32,21 @@ def get_srid_info(srid, connection):
         # The SpatialRefSys model for the spatial backend.
         SpatialRefSys = connection.ops.spatial_ref_sys()
     except NotImplementedError:
-        # No `spatial_ref_sys` table in spatial backend (e.g., MySQL).
+        SpatialRefSys = None
-        return None, None, None
 
-    if connection.alias not in _srid_cache:
+    alias, get_srs = (
-        # Initialize SRID dictionary for database if it doesn't exist.
+        (connection.alias, lambda srid: SpatialRefSys.objects.using(connection.alias).get(srid=srid).srs)
-        _srid_cache[connection.alias] = {}
+        if SpatialRefSys else
+        (None, SpatialReference)
+    )
+    if srid not in _srid_cache[alias]:
+        srs = get_srs(srid)
+        units, units_name = srs.units
+        sphere_name = srs['spheroid']
+        spheroid = 'SPHEROID["%s",%s,%s]' % (sphere_name, srs.semi_major, srs.inverse_flattening)
+        _srid_cache[alias][srid] = (units, units_name, spheroid)
 
-    if srid not in _srid_cache[connection.alias]:
+    return _srid_cache[alias][srid]
-        # Use `SpatialRefSys` model to query for spatial reference info.
-        sr = SpatialRefSys.objects.using(connection.alias).get(srid=srid)
-        units, units_name = sr.units
-        spheroid = SpatialRefSys.get_spheroid(sr.wkt)
-        _srid_cache[connection.alias][srid] = (units, units_name, spheroid)
-
-    return _srid_cache[connection.alias][srid]
 
 
 class GeoSelectFormatMixin(object):
@@ -149,8 +152,6 @@ class BaseSpatialField(Field):
         system that uses non-projected units (e.g., latitude/longitude).
         """
         units_name = self.units_name(connection)
-        # Some backends like MySQL cannot determine units name. In that case,
-        # test if srid is 4326 (WGS84), even if this is over-simplification.
         return units_name.lower() in self.geodetic_units if units_name else self.srid == 4326
 
     def get_placeholder(self, value, compiler, connection):

docs/ref/contrib/gis/functions.txt

@@ -41,8 +41,12 @@ Measurement         Relationships             Operations              Editors
 
 Accepts a single geographic field or expression and returns the area of the
 field as an :class:`~django.contrib.gis.measure.Area` measure. On MySQL, a raw
-float value is returned, as it's not possible to automatically determine the
+float value is returned when the coordinates are geodetic.
-unit of the field.
+
+.. versionchanged:: 1.11
+
+    In older versions, a raw value was returned on MySQL when used on
+    projected SRS.
 
 ``AsGeoJSON``
 =============
@@ -211,8 +215,7 @@ geometry B.
 
 Accepts two geographic fields or expressions and returns the distance between
 them, as a :class:`~django.contrib.gis.measure.Distance` object. On MySQL, a raw
-float value is returned, as it's not possible to automatically determine the
+float value is returned when the coordinates are geodetic.
-unit of the field.
 
 On backends that support distance calculation on geodetic coordinates, the
 proper backend function is automatically chosen depending on the SRID value of
@@ -246,6 +249,11 @@ queryset is calculated::
     in kilometers. See :doc:`measure` for usage details and the list of
     :ref:`supported_units`.
 
+.. versionchanged:: 1.11
+
+    In older versions, a raw value was returned on MySQL when used on
+    projected SRS.
+
 ``Envelope``
 ============
 
@@ -325,14 +333,19 @@ Returns ``True`` if its value is a valid geometry and ``False`` otherwise.
 
 Accepts a single geographic linestring or multilinestring field or expression
 and returns its length as an :class:`~django.contrib.gis.measure.Distance`
-measure. On MySQL, a raw float value is returned, as it's not possible to
+measure. On MySQL, a raw float value is returned when the coordinates
-automatically determine the unit of the field.
+are geodetic.
 
 On PostGIS and SpatiaLite, when the coordinates are geodetic (angular), you can
 specify if the calculation should be based on a simple sphere (less
 accurate, less resource-intensive) or on a spheroid (more accurate, more
 resource-intensive) with the ``spheroid`` keyword argument.
 
+.. versionchanged:: 1.11
+
+    In older versions, a raw value was returned on MySQL when used on
+    projected SRS.
+
 ``MakeValid``
 =============
 

tests/gis_tests/distapp/tests.py

@@ -475,8 +475,7 @@ class DistanceFunctionsTests(TestCase):
         # Tolerance has to be lower for Oracle
         tol = 2
         for i, z in enumerate(SouthTexasZipcode.objects.annotate(area=Area('poly')).order_by('name')):
-            # MySQL is returning a raw float value
+            self.assertAlmostEqual(area_sq_m[i], z.area.sq_m, tol)
-            self.assertAlmostEqual(area_sq_m[i], z.area.sq_m if hasattr(z.area, 'sq_m') else z.area, tol)
 
     @skipUnlessDBFeature("has_Distance_function")
     def test_distance_simple(self):
@@ -488,7 +487,7 @@ class DistanceFunctionsTests(TestCase):
         houston = SouthTexasCity.objects.annotate(dist=Distance('point', lagrange)).order_by('id').first()
         tol = 2 if oracle else 5
         self.assertAlmostEqual(
-            houston.dist.m if hasattr(houston.dist, 'm') else houston.dist,
+            houston.dist.m,
             147075.069813,
             tol
         )
@@ -656,7 +655,7 @@ class DistanceFunctionsTests(TestCase):
 
         # Now doing length on a projected coordinate system.
         i10 = SouthTexasInterstate.objects.annotate(length=Length('path')).get(name='I-10')
-        self.assertAlmostEqual(len_m2, i10.length.m if isinstance(i10.length, D) else i10.length, 2)
+        self.assertAlmostEqual(len_m2, i10.length.m, 2)
         self.assertTrue(
             SouthTexasInterstate.objects.annotate(length=Length('path')).filter(length__gt=4000).exists()
         )