Refs #20888 -- Added index order introspection.

django/db/backends/base/features.py

@@ -160,6 +160,9 @@ class BaseDatabaseFeatures(object):
     # Can the backend introspect a TimeField, instead of a DateTimeField?
     can_introspect_time_field = True
 
+    # Can the backend introspect the column order (ASC/DESC) for indexes?
+    supports_index_column_ordering = True
+
     # Support for the DISTINCT ON clause
     can_distinct_on_fields = False
 

django/db/backends/mysql/features.py

@@ -24,6 +24,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     can_introspect_autofield = True
     can_introspect_binary_field = False
     can_introspect_small_integer_field = True
+    supports_index_column_ordering = False
     supports_timezones = False
     requires_explicit_null_ordering_when_grouping = True
     allows_auto_pk_0 = False

django/db/backends/oracle/introspection.py

@@ -259,7 +259,7 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
         cursor.execute("""
             SELECT
                 index_name,
-                LOWER(column_name)
+                LOWER(column_name), descend
             FROM
                 user_ind_columns cols
             WHERE
@@ -271,11 +271,12 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
                 )
             ORDER BY cols.column_position
         """, [table_name])
-        for constraint, column in cursor.fetchall():
+        for constraint, column, order in cursor.fetchall():
             # If we're the first column, make the record
             if constraint not in constraints:
                 constraints[constraint] = {
                     "columns": [],
+                    "orders": [],
                     "primary_key": False,
                     "unique": False,
                     "foreign_key": None,
@@ -284,4 +285,5 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
                 }
             # Record the details
             constraints[constraint]['columns'].append(column)
+            constraints[constraint]['orders'].append(order)
         return constraints

django/db/backends/postgresql/introspection.py

@@ -211,23 +211,36 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
         # Now get indexes
         cursor.execute("""
             SELECT
-                c2.relname,
-                ARRAY(
-                    SELECT (SELECT attname FROM pg_catalog.pg_attribute WHERE attnum = i AND attrelid = c.oid)
-                    FROM unnest(idx.indkey) i
-                ),
-                idx.indisunique,
-                idx.indisprimary
-            FROM pg_catalog.pg_class c, pg_catalog.pg_class c2,
-                pg_catalog.pg_index idx
-            WHERE c.oid = idx.indrelid
-                AND idx.indexrelid = c2.oid
-                AND c.relname = %s
+                indexname, array_agg(attname), indisunique, indisprimary,
+                array_agg(ordering)
+            FROM (
+                SELECT
+                    c2.relname as indexname, idx.*, attr.attname,
+                    CASE
+                        WHEN am.amcanorder THEN
+                            CASE (option & 1)
+                                WHEN 1 THEN 'DESC' ELSE 'ASC'
+                            END
+                    END as ordering
+                FROM (
+                    SELECT
+                        *, unnest(i.indkey) as key, unnest(i.indoption) as option
+                    FROM pg_index i
+                ) idx, pg_class c, pg_class c2, pg_am am, pg_attribute attr
+                WHERE c.oid=idx.indrelid
+                    AND idx.indexrelid=c2.oid
+                    AND attr.attrelid=c.oid
+                    AND attr.attnum=idx.key
+                    AND c2.relam=am.oid
+                    AND c.relname = %s
+            ) s2
+            GROUP BY indexname, indisunique, indisprimary;
         """, [table_name])
-        for index, columns, unique, primary in cursor.fetchall():
+        for index, columns, unique, primary, orders in cursor.fetchall():
             if index not in constraints:
                 constraints[index] = {
-                    "columns": list(columns),
+                    "columns": columns,
+                    "orders": orders,
                     "primary_key": primary,
                     "unique": unique,
                     "foreign_key": None,

django/db/backends/sqlite3/features.py

@@ -45,6 +45,10 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     def uses_savepoints(self):
         return Database.sqlite_version_info >= (3, 6, 8)
 
+    @cached_property
+    def supports_index_column_ordering(self):
+        return Database.sqlite_version_info >= (3, 3, 0)
+
     @cached_property
     def can_release_savepoints(self):
         return self.uses_savepoints

django/db/backends/sqlite3/introspection.py

@@ -255,6 +255,18 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
                         "index": True,
                     }
                 constraints[index]['columns'].append(column)
+            # Add column orders for indexes
+            if constraints[index]['index'] and not constraints[index]['unique']:
+                cursor.execute(
+                    "SELECT sql FROM sqlite_master "
+                    "WHERE type='index' AND name=%s" % self.connection.ops.quote_name(index)
+                )
+                orders = []
+                # There would be only 1 row to loop over
+                for sql, in cursor.fetchall():
+                    order_info = sql.split('(')[-1].split(')')[0].split(',')
+                    orders = ['DESC' if info.endswith('DESC') else 'ASC' for info in order_info]
+                constraints[index]['orders'] = orders
         # Get the PK
         pk_column = self.get_primary_key_column(cursor, table_name)
         if pk_column:

docs/releases/1.11.txt

@@ -311,6 +311,13 @@ Database backend API
 * To enable ``FOR UPDATE SKIP LOCKED`` support, set
   ``DatabaseFeatures.has_select_for_update_skip_locked = True``.
 
+* The new ``DatabaseFeatures.supports_index_column_ordering`` attribute
+  specifies if a database allows defining ordering for columns in indexes. The
+  default value is ``True`` and the ``DatabaseIntrospection.get_constraints()``
+  method should include an ``'orders'`` key in each of the returned
+  dictionaries with a list of ``'ASC'`` and/or ``'DESC'`` values corresponding
+  to the the ordering of each column in the index.
+
 Dropped support for PostgreSQL 9.2 and PostGIS 2.0
 --------------------------------------------------
 

tests/introspection/tests.py

@@ -182,6 +182,26 @@ class IntrospectionTests(TransactionTestCase):
         self.assertNotIn('first_name', indexes)
         self.assertIn('id', indexes)
 
+    @skipUnlessDBFeature('supports_index_column_ordering')
+    def test_get_constraints_indexes_orders(self):
+        """
+        Indexes have the 'orders' key with a list of 'ASC'/'DESC' values.
+        """
+        with connection.cursor() as cursor:
+            constraints = connection.introspection.get_constraints(cursor, Article._meta.db_table)
+        indexes_verified = 0
+        expected_columns = [
+            ['reporter_id'],
+            ['headline', 'pub_date'],
+            ['response_to_id'],
+        ]
+        for key, val in constraints.items():
+            if val['index'] and not (val['primary_key'] or val['unique']):
+                self.assertIn(val['columns'], expected_columns)
+                self.assertEqual(val['orders'], ['ASC'] * len(val['columns']))
+                indexes_verified += 1
+        self.assertEqual(indexes_verified, 3)
+
 
 def datatype(dbtype, description):
     """Helper to convert a data type into a string."""