Removed connection agnostic SRID info cache from BaseSpatialField.

django/contrib/gis/db/backends/postgis/operations.py

@@ -96,7 +96,7 @@ class PostGISDistanceOperator(PostGISOperator):
                 sql_template = '%(func)s(%(lhs)s, %(rhs)s, %%s) %(op)s %(value)s'
                 # Using DistanceSpheroid requires the spheroid of the field as
                 # a parameter.
-                sql_params.insert(1, lookup.lhs.output_field._spheroid)
+                sql_params.insert(1, lookup.lhs.output_field.spheroid(connection))
             else:
                 template_params.update({'op': self.op, 'func': connection.ops.spatial_function_name('DistanceSphere')})
             return sql_template % template_params, sql_params

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

@@ -115,26 +115,14 @@ class BaseSpatialField(Field):
     def db_type(self, connection):
         return connection.ops.geo_db_type(self)
 
-    # The following functions are used to get the units, their name, and
-    # the spheroid corresponding to the SRID of the BaseSpatialField.
-    def _get_srid_info(self, connection):
-        # Get attributes from `get_srid_info`.
-        self._units, self._units_name, self._spheroid = get_srid_info(self.srid, connection)
-
     def spheroid(self, connection):
-        if not hasattr(self, '_spheroid'):
-            self._get_srid_info(connection)
-        return self._spheroid
+        return get_srid_info(self.srid, connection)[2]
 
     def units(self, connection):
-        if not hasattr(self, '_units'):
-            self._get_srid_info(connection)
-        return self._units
+        return get_srid_info(self.srid, connection)[0]
 
     def units_name(self, connection):
-        if not hasattr(self, '_units_name'):
-            self._get_srid_info(connection)
-        return self._units_name
+        return get_srid_info(self.srid, connection)[1]
 
     def geodetic(self, connection):
         """

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

@@ -301,7 +301,7 @@ class Distance(DistanceResultMixin, OracleToleranceMixin, GeoFunc):
                 # DistanceSpheroid is more accurate and resource intensive than DistanceSphere
                 function = connection.ops.spatial_function_name('DistanceSpheroid')
                 # Replace boolean param by the real spheroid of the base field
-                self.source_expressions[2] = Value(geo_field._spheroid)
+                self.source_expressions[2] = Value(geo_field.spheroid(connection))
             else:
                 function = connection.ops.spatial_function_name('DistanceSphere')
         return super().as_sql(compiler, connection, function=function)
@@ -380,7 +380,7 @@ class Length(DistanceResultMixin, OracleToleranceMixin, GeoFunc):
         elif geo_field.geodetic(connection):
             # Geometry fields with geodetic (lon/lat) coordinates need length_spheroid
             function = connection.ops.spatial_function_name('LengthSpheroid')
-            self.source_expressions.append(Value(geo_field._spheroid))
+            self.source_expressions.append(Value(geo_field.spheroid(connection)))
         else:
             dim = min(f.dim for f in self.get_source_fields() if f)
             if dim > 2: