Add additional caution looking for table, info4.13.3

A joined inheritance mapper is mapped to a join();
these have no .info attribute, so use that
of the local table instead.  The sorting order when
querying against a joined subclass table
can at least be derived from the base table, so
use the base mapper's table.  It may be a better idea
to comprise the constraints amongst the base table
*and* the joined table, though.

Change-Id: I9466c9dbbbdc4af10ab0f15ee0f558199973c1ec
(cherry picked from commit b19738a13a08f9ff5ac2357060250d121c680163)

1 files changed, 13 insertions, 8 deletions

diff --git a/oslo_db/sqlalchemy/utils.py b/oslo_db/sqlalchemy/utils.py
index 016bae7..c5030a0 100644
--- a/oslo_db/sqlalchemy/utils.py
+++ b/oslo_db/sqlalchemy/utils.py
@@ -80,18 +80,22 @@ def _get_unique_keys(model):
     except exc.NoInspectionAvailable:
         return None
     else:
-        table = mapper.mapped_table
-        if table is None:
+        local_table = mapper.local_table
+        base_table = mapper.base_mapper.local_table
+
+        if local_table is None:
             return None
 
     # extract result from cache if present
-    info = table.info
-    if 'oslodb_unique_keys' in info:
-        return info['oslodb_unique_keys']
+    has_info = hasattr(local_table, 'info')
+    if has_info:
+        info = local_table.info
+        if 'oslodb_unique_keys' in info:
+            return info['oslodb_unique_keys']
 
     res = []
     try:
-        constraints = table.constraints
+        constraints = base_table.constraints
     except AttributeError:
         constraints = []
     for constraint in constraints:
@@ -100,14 +104,15 @@ def _get_unique_keys(model):
                                    sqlalchemy.PrimaryKeyConstraint)):
             res.append({c.name for c in constraint.columns})
     try:
-        indexes = table.indexes
+        indexes = base_table.indexes
     except AttributeError:
         indexes = []
     for index in indexes:
         if index.unique:
             res.append({c.name for c in index.columns})
     # cache result for next calls with the same model
-    info['oslodb_unique_keys'] = res
+    if has_info:
+        info['oslodb_unique_keys'] = res
     return res