Made get_indexes() consistent across backends.

Fixed #15933, #18082 -- the get_indexes() method introspection was
done inconsitently depending on the backend. For example SQLite
included all the columns in the table in the returned dictionary,
while MySQL introspected also multicolumn indexes.

All backends return now consistenly only single-column indexes.

Thanks to andi for the MySQL report, and ikelly for comments on
Oracle's get_indexes() changes.

django/db/backends/__init__.py

@@ -997,6 +997,17 @@ class BaseDatabaseIntrospection(object):
         """
         raise NotImplementedError
 
+    def get_indexes(self, cursor, table_name):
+        """
+        Returns a dictionary of indexed fieldname -> infodict for the given
+        table, where each infodict is in the format:
+            {'primary_key': boolean representing whether it's the primary key,
+             'unique': boolean representing whether it's a unique index}
+
+        Only single-column indexes are introspected.
+        """
+        raise NotImplementedError
+
 class BaseDatabaseClient(object):
     """
     This class encapsulates all backend-specific methods for opening a

django/db/backends/mysql/introspection.py

@@ -85,15 +85,19 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
         return None
 
     def get_indexes(self, cursor, table_name):
-        """
-        Returns a dictionary of fieldname -> infodict for the given table,
-        where each infodict is in the format:
-            {'primary_key': boolean representing whether it's the primary key,
-             'unique': boolean representing whether it's a unique index}
-        """
         cursor.execute("SHOW INDEX FROM %s" % self.connection.ops.quote_name(table_name))
+        # Do a two-pass search for indexes: on first pass check which indexes
+        # are multicolumn, on second pass check which single-column indexes
+        # are present.
+        rows = list(cursor.fetchall())
+        multicol_indexes = set()
+        for row in rows:
+            if row[3] > 1:
+                multicol_indexes.add(row[2])
         indexes = {}
-        for row in cursor.fetchall():
+        for row in rows:
+            if row[2] in multicol_indexes:
+                continue
             indexes[row[4]] = {'primary_key': (row[2] == 'PRIMARY'), 'unique': not bool(row[1])}
         return indexes
 

django/db/backends/oracle/introspection.py

@@ -72,14 +72,14 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
     FROM   user_constraints, USER_CONS_COLUMNS ca, USER_CONS_COLUMNS cb,
            user_tab_cols ta, user_tab_cols tb
     WHERE  user_constraints.table_name = %s AND
-           ta.table_name = %s AND
+           ta.table_name = user_constraints.table_name AND
            ta.column_name = ca.column_name AND
-           ca.table_name = %s AND
+           ca.table_name = ta.table_name AND
            user_constraints.constraint_name = ca.constraint_name AND
            user_constraints.r_constraint_name = cb.constraint_name AND
            cb.table_name = tb.table_name AND
            cb.column_name = tb.column_name AND
-           ca.position = cb.position""", [table_name, table_name, table_name])
+           ca.position = cb.position""", [table_name])
 
         relations = {}
         for row in cursor.fetchall():
@@ -87,36 +87,31 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
         return relations
 
     def get_indexes(self, cursor, table_name):
-        """
+        sql = """
-        Returns a dictionary of fieldname -> infodict for the given table,
+    SELECT LOWER(uic1.column_name) AS column_name,
-        where each infodict is in the format:
-            {'primary_key': boolean representing whether it's the primary key,
-             'unique': boolean representing whether it's a unique index}
-        """
-        # This query retrieves each index on the given table, including the
-        # first associated field name
-        # "We were in the nick of time; you were in great peril!"
-        sql = """\
-SELECT LOWER(all_tab_cols.column_name) AS column_name,
            CASE user_constraints.constraint_type
                WHEN 'P' THEN 1 ELSE 0
            END AS is_primary_key,
            CASE user_indexes.uniqueness
                WHEN 'UNIQUE' THEN 1 ELSE 0
            END AS is_unique
-FROM   all_tab_cols, user_cons_columns, user_constraints, user_ind_columns, user_indexes
+    FROM   user_constraints, user_indexes, user_ind_columns uic1
-WHERE  all_tab_cols.column_name = user_cons_columns.column_name (+)
+    WHERE  user_constraints.constraint_type (+) = 'P'
-  AND  all_tab_cols.table_name = user_cons_columns.table_name (+)
+      AND  user_constraints.index_name (+) = uic1.index_name
-  AND  user_cons_columns.constraint_name = user_constraints.constraint_name (+)
-  AND  user_constraints.constraint_type (+) = 'P'
-  AND  user_ind_columns.column_name (+) = all_tab_cols.column_name
-  AND  user_ind_columns.table_name (+) = all_tab_cols.table_name
       AND  user_indexes.uniqueness (+) = 'UNIQUE'
-  AND  user_indexes.index_name (+) = user_ind_columns.index_name
+      AND  user_indexes.index_name (+) = uic1.index_name
-  AND  all_tab_cols.table_name = UPPER(%s)
+      AND  uic1.table_name = UPPER(%s)
-"""
+      AND  uic1.column_position = 1
+      AND  NOT EXISTS (
+              SELECT 1
+              FROM   user_ind_columns uic2
+              WHERE  uic2.index_name = uic1.index_name
+                AND  uic2.column_position = 2
+           )
+        """
         cursor.execute(sql, [table_name])
         indexes = {}
         for row in cursor.fetchall():
-            indexes[row[0]] = {'primary_key': row[1], 'unique': row[2]}
+            indexes[row[0]] = {'primary_key': bool(row[1]),
+                               'unique': bool(row[2])}
         return indexes

django/db/backends/postgresql_psycopg2/introspection.py

@@ -65,12 +65,6 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
         return relations
 
     def get_indexes(self, cursor, table_name):
-        """
-        Returns a dictionary of fieldname -> infodict for the given table,
-        where each infodict is in the format:
-            {'primary_key': boolean representing whether it's the primary key,
-             'unique': boolean representing whether it's a unique index}
-        """
         # This query retrieves each index on the given table, including the
         # first associated field name
         cursor.execute("""

django/db/backends/sqlite3/introspection.py

@@ -133,28 +133,22 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
         return key_columns
 
     def get_indexes(self, cursor, table_name):
-        """
-        Returns a dictionary of fieldname -> infodict for the given table,
-        where each infodict is in the format:
-            {'primary_key': boolean representing whether it's the primary key,
-             'unique': boolean representing whether it's a unique index}
-        """
         indexes = {}
         for info in self._table_info(cursor, table_name):
-            indexes[info['name']] = {'primary_key': info['pk'] != 0,
+            if info['pk'] != 0:
+                indexes[info['name']] = {'primary_key': True,
                                          'unique': False}
         cursor.execute('PRAGMA index_list(%s)' % self.connection.ops.quote_name(table_name))
         # seq, name, unique
         for index, unique in [(field[1], field[2]) for field in cursor.fetchall()]:
-            if not unique:
-                continue
             cursor.execute('PRAGMA index_info(%s)' % self.connection.ops.quote_name(index))
             info = cursor.fetchall()
             # Skip indexes across multiple fields
             if len(info) != 1:
                 continue
             name = info[0][2] # seqno, cid, name
-            indexes[name]['unique'] = True
+            indexes[name] = {'primary_key': False,
+                             'unique': unique}
         return indexes
 
     def get_primary_key_column(self, cursor, table_name):

tests/regressiontests/introspection/models.py

@@ -7,6 +7,9 @@ class Reporter(models.Model):
     email = models.EmailField()
     facebook_user_id = models.BigIntegerField(null=True)
 
+    class Meta:
+        unique_together = ('first_name', 'last_name')
+
     def __unicode__(self):
         return u"%s %s" % (self.first_name, self.last_name)
 

tests/regressiontests/introspection/tests.py

@@ -137,6 +137,15 @@ class IntrospectionTests(TestCase):
         indexes = connection.introspection.get_indexes(cursor, Article._meta.db_table)
         self.assertEqual(indexes['reporter_id'], {'unique': False, 'primary_key': False})
 
+    def test_get_indexes_multicol(self):
+        """
+        Test that multicolumn indexes are not included in the introspection
+        results.
+        """
+        cursor = connection.cursor()
+        indexes = connection.introspection.get_indexes(cursor, Reporter._meta.db_table)
+        self.assertNotIn('first_name', indexes)
+        self.assertIn('id', indexes)
 
 def datatype(dbtype, description):
     """Helper to convert a data type into a string."""