Fixed #7783 -- Made introspection of nullable columns more robust with Postgres.

Thanks bthomas AT ncorcle DOT com for the report and initial patch, and
Claude Paroz for the final, complete patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@17508 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/backends/postgresql_psycopg2/introspection.py

@@ -34,8 +34,16 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
 
     def get_table_description(self, cursor, table_name):
         "Returns a description of the table, with the DB-API cursor.description interface."
+        # As cursor.description does not return reliably the nullable property,
+        # we have to query the information_schema (#7783)
+        cursor.execute("""
+            SELECT column_name, is_nullable
+            FROM information_schema.columns
+            WHERE table_name = %s""", [table_name])
+        null_map = dict(cursor.fetchall())
         cursor.execute("SELECT * FROM %s LIMIT 1" % self.connection.ops.quote_name(table_name))
-        return cursor.description
+        return [tuple([item for item in line[:6]] + [null_map[line[0]]==u'YES'])
+            for line in cursor.description]
 
     def get_relations(self, cursor, table_name):
         """

tests/regressiontests/introspection/models.py

@@ -5,7 +5,7 @@ class Reporter(models.Model):
     first_name = models.CharField(max_length=30)
     last_name = models.CharField(max_length=30)
     email = models.EmailField()
-    facebook_user_id = models.BigIntegerField()
+    facebook_user_id = models.BigIntegerField(null=True)
 
     def __unicode__(self):
         return u"%s %s" % (self.first_name, self.last_name)

tests/regressiontests/introspection/tests.py

@@ -78,6 +78,14 @@ class IntrospectionTests(TestCase):
             ['IntegerField', 'CharField', 'CharField', 'CharField', 'BigIntegerField']
         )
 
+    def test_get_table_description_nullable(self):
+        cursor = connection.cursor()
+        desc = connection.introspection.get_table_description(cursor, Reporter._meta.db_table)
+        self.assertEqual(
+            [r[6] for r in desc],
+            [False, False, False, False, True]
+        )
+
     # Regression test for #9991 - 'real' types in postgres
     @skipUnlessDBFeature('has_real_datatype')
     def test_postgresql_real_type(self):