From 8d01edfa65859d2ad5f91ad74745862d0eb91eb0 Mon Sep 17 00:00:00 2001
From: Nick Pope <nick.pope@flightdataservices.com>
Date: Sat, 19 Jan 2019 14:37:16 +0000
Subject: [PATCH] Refs #30123 -- Simplified introspection of geography columns
 on PostGIS.

---
 .../gis/db/backends/postgis/introspection.py  | 51 +++++--------------
 1 file changed, 13 insertions(+), 38 deletions(-)

diff --git a/django/contrib/gis/db/backends/postgis/introspection.py b/django/contrib/gis/db/backends/postgis/introspection.py
index 66c5bb5d42a..0647012b047 100644
--- a/django/contrib/gis/db/backends/postgis/introspection.py
+++ b/django/contrib/gis/db/backends/postgis/introspection.py
@@ -3,9 +3,7 @@ from django.db.backends.postgresql.introspection import DatabaseIntrospection
 
 
 class PostGISIntrospection(DatabaseIntrospection):
-    # Reverse dictionary for PostGIS geometry types not populated until
-    # introspection is actually performed.
-    postgis_types_reverse = {}
+    postgis_oid_lookup = {}  # Populated when introspection is performed.
 
     ignored_tables = DatabaseIntrospection.ignored_tables + [
         'geography_columns',
@@ -15,42 +13,17 @@ class PostGISIntrospection(DatabaseIntrospection):
         'raster_overviews',
     ]
 
-    def get_postgis_types(self):
-        """
-        Return a dictionary with keys that are the PostgreSQL object
-        identification integers for the PostGIS geometry and/or
-        geography types (if supported).
-        """
-        field_types = [
-            ('geometry', 'GeometryField'),
-            # The value for the geography type is actually a tuple
-            # to pass in the `geography=True` keyword to the field
-            # definition.
-            ('geography', ('GeometryField', {'geography': True})),
-        ]
-        postgis_types = {}
-
-        # The OID integers associated with the geometry type may
-        # be different across versions; hence, this is why we have
-        # to query the PostgreSQL pg_type table corresponding to the
-        # PostGIS custom data types.
-        oid_sql = 'SELECT "oid" FROM "pg_type" WHERE "typname" = %s'
-        with self.connection.cursor() as cursor:
-            for field_type in field_types:
-                cursor.execute(oid_sql, (field_type[0],))
-                for result in cursor.fetchall():
-                    postgis_types[result[0]] = field_type[1]
-        return postgis_types
-
     def get_field_type(self, data_type, description):
-        if not self.postgis_types_reverse:
-            # If the PostGIS types reverse dictionary is not populated, do so
-            # now.  In order to prevent unnecessary requests upon connection
-            # initialization, the `data_types_reverse` dictionary is not updated
-            # with the PostGIS custom types until introspection is actually
-            # performed -- in other words, when this function is called.
-            self.postgis_types_reverse = self.get_postgis_types()
-            self.data_types_reverse.update(self.postgis_types_reverse)
+        if not self.postgis_oid_lookup:
+            # Query PostgreSQL's pg_type table to determine the OID integers
+            # for the PostGIS data types used in reverse lookup (the integers
+            # may be different across versions). To prevent unnecessary
+            # requests upon connection initialization, the `data_types_reverse`
+            # dictionary isn't updated until introspection is performed here.
+            with self.connection.cursor() as cursor:
+                cursor.execute("SELECT oid, typname FROM pg_type WHERE typname IN ('geometry', 'geography')")
+                self.postgis_oid_lookup = dict(cursor.fetchall())
+            self.data_types_reverse.update((oid, 'GeometryField') for oid in self.postgis_oid_lookup)
         return super().get_field_type(data_type, description)
 
     def get_geometry_type(self, table_name, description):
@@ -78,6 +51,8 @@ class PostGISIntrospection(DatabaseIntrospection):
             field_type = OGRGeomType(field_type).django
             # Getting any GeometryField keyword arguments that are not the default.
             field_params = {}
+            if self.postgis_oid_lookup.get(description.type_code) == 'geography':
+                field_params['geography'] = True
             if srid != 4326:
                 field_params['srid'] = srid
             if dim != 2: