Fixed #17574 -- Implemented missing get_key_columns in PostgreSQL backend

django/db/backends/postgresql_psycopg2/introspection.py

@@ -66,6 +66,23 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
             relations[row[0][0] - 1] = (row[1][0] - 1, row[2])
         return relations
 
+    def get_key_columns(self, cursor, table_name):
+        key_columns = []
+        cursor.execute("""
+            SELECT kcu.column_name, ccu.table_name AS referenced_table, ccu.column_name AS referenced_column
+            FROM information_schema.constraint_column_usage ccu
+            LEFT JOIN information_schema.key_column_usage kcu
+                ON ccu.constraint_catalog = kcu.constraint_catalog
+                    AND ccu.constraint_schema = kcu.constraint_schema
+                    AND ccu.constraint_name = kcu.constraint_name
+            LEFT JOIN information_schema.table_constraints tc
+                ON ccu.constraint_catalog = tc.constraint_catalog
+                    AND ccu.constraint_schema = tc.constraint_schema
+                    AND ccu.constraint_name = tc.constraint_name
+            WHERE kcu.table_name = %s AND tc.constraint_type = 'FOREIGN KEY'""" , [table_name])
+        key_columns.extend(cursor.fetchall())
+        return key_columns
+
     def get_indexes(self, cursor, table_name):
         # This query retrieves each index on the given table, including the
         # first associated field name

tests/regressiontests/introspection/tests.py

@@ -1,10 +1,8 @@
 from __future__ import absolute_import, unicode_literals
 
-from functools import update_wrapper
-
 from django.db import connection
 from django.test import TestCase, skipUnlessDBFeature, skipIfDBFeature
-from django.utils import six, unittest
+from django.utils import unittest
 
 from .models import Reporter, Article
 
@@ -14,36 +12,7 @@ else:
     expectedFailureOnOracle = lambda f: f
 
 
-# The introspection module is optional, so methods tested here might raise
-# NotImplementedError. This is perfectly acceptable behavior for the backend
-# in question, but the tests need to handle this without failing. Ideally we'd
-# skip these tests, but until #4788 is done we'll just ignore them.
-#
-# The easiest way to accomplish this is to decorate every test case with a
-# wrapper that ignores the exception.
-#
-# The metaclass is just for fun.
-
-
-def ignore_not_implemented(func):
-    def _inner(*args, **kwargs):
-        try:
-            return func(*args, **kwargs)
-        except NotImplementedError:
-            return None
-    update_wrapper(_inner, func)
-    return _inner
-
-
-class IgnoreNotimplementedError(type):
-    def __new__(cls, name, bases, attrs):
-        for k, v in attrs.items():
-            if k.startswith('test'):
-                attrs[k] = ignore_not_implemented(v)
-        return type.__new__(cls, name, bases, attrs)
-
-
-class IntrospectionTests(six.with_metaclass(IgnoreNotimplementedError, TestCase)):
+class IntrospectionTests(TestCase):
     def test_table_names(self):
         tl = connection.introspection.table_names()
         self.assertEqual(tl, sorted(tl))
@@ -139,6 +108,7 @@ class IntrospectionTests(six.with_metaclass(IgnoreNotimplementedError, TestCase)
             # That's {field_index: (field_index_other_table, other_table)}
             self.assertEqual(relations, {3: (0, Reporter._meta.db_table)})
 
+    @skipUnlessDBFeature('can_introspect_foreign_keys')
     def test_get_key_columns(self):
         cursor = connection.cursor()
         key_columns = connection.introspection.get_key_columns(cursor, Article._meta.db_table)