Implemented some SpatiaLiteOperations as cached properties

Previously, some properties weren't set unless
confirm_spatial_components_versions() was explicitely called.

django/contrib/gis/db/backends/spatialite/creation.py

@@ -30,7 +30,6 @@ def create_test_db(self, verbosity=1, autoclobber=False):
 
         self.connection.close()
         self.connection.settings_dict["NAME"] = test_database_name
-        self.connection.ops.confirm_spatial_components_versions()
 
         # Need to load the SpatiaLite initialization SQL before running `syncdb`.
         self.load_spatialite_sql()

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

@@ -10,6 +10,8 @@
 from django.db.backends.sqlite3.base import DatabaseOperations
 from django.db.utils import DatabaseError
 from django.utils import six
+from django.utils.functional import cached_property
+
 
 class SpatiaLiteOperator(SpatialOperation):
     "For SpatiaLite operators (e.g. `&&`, `~`)."
@@ -118,36 +120,48 @@ def __init__(self, connection):
         gis_terms += self.geometry_functions.keys()
         self.gis_terms = dict([(term, None) for term in gis_terms])
 
-    def confirm_spatial_components_versions(self):
-        # Determine the version of the SpatiaLite library.
+    @cached_property
+    def spatial_version(self):
+        """Determine the version of the SpatiaLite library."""
         try:
-            vtup = self.spatialite_version_tuple()
-            version = vtup[1:]
-            if version < (2, 3, 0):
-                raise ImproperlyConfigured('GeoDjango only supports SpatiaLite versions '
-                                           '2.3.0 and above')
-            self.spatial_version = version
-        except ImproperlyConfigured:
-            raise
+            version = self.spatialite_version_tuple()[1:]
         except Exception as msg:
             raise ImproperlyConfigured('Cannot determine the SpatiaLite version for the "%s" '
                                        'database (error was "%s").  Was the SpatiaLite initialization '
                                        'SQL loaded on this database?' %
                                        (self.connection.settings_dict['NAME'], msg))
-
-        if version >= (2, 4, 0):
+        if version < (2, 3, 0):
+            raise ImproperlyConfigured('GeoDjango only supports SpatiaLite versions '
+                                       '2.3.0 and above')
+        return version
+
+    @property
+    def _version_greater_2_4_0_rc4(self):
+        if self.spatial_version >= (2, 4, 1):
+            return True
+        elif self.spatial_version < (2, 4, 0):
+            return False
+        else:
             # Spatialite 2.4.0-RC4 added AsGML and AsKML, however both
             # RC2 (shipped in popular Debian/Ubuntu packages) and RC4
             # report version as '2.4.0', so we fall back to feature detection
             try:
                 self._get_spatialite_func("AsGML(GeomFromText('POINT(1 1)'))")
-                self.gml = 'AsGML'
-                self.kml = 'AsKML'
             except DatabaseError:
-                # we are using < 2.4.0-RC4
-                pass
-        if version >= (3, 0, 0):
-            self.geojson = 'AsGeoJSON'
+                return False
+            return True
+
+    @cached_property
+    def gml(self):
+        return 'AsGML' if self._version_greater_2_4_0_rc4 else None
+
+    @cached_property
+    def kml(self):
+        return 'AsKML' if self._version_greater_2_4_0_rc4 else None
+
+    @cached_property
+    def geojson(self):
+        return 'AsGeoJSON' if self.spatial_version >= (3, 0, 0) else None
 
     def check_aggregate_support(self, aggregate):
         """