Implement relationship to AliasedClass; deprecate non primary mappers

Implemented a new feature whereby the :class:`.AliasedClass` construct can
now be used as the target of a :func:`.relationship`.  This allows the
concept of "non primary mappers" to no longer be necessary, as the
:class:`.AliasedClass` is much easier to configure and automatically inherits
all the relationships of the mapped class, as well as preserves the
ability for loader options to work normally.

- introduce new name for mapped_table, "persist_selectable".  this is
the selectable that selects against the local mapper and its superclasses,
but does not include columns local only to subclasses.

- relationship gains "entity" which is the mapper or aliasedinsp.

- clarfiy name "entity" vs. "query_entity" in loader strategies.

Fixes: #4423
Fixes: #4422
Fixes: #4421
Fixes: #3348

Change-Id: Ic3609b43dc4ed115006da9ad9189e574dc0c72d9

1 files changed, 3 insertions, 3 deletions

diff --git a/lib/sqlalchemy/orm/session.py b/lib/sqlalchemy/orm/session.py
index 53f99b99d..a4cc07194 100644
--- a/lib/sqlalchemy/orm/session.py
+++ b/lib/sqlalchemy/orm/session.py
@@ -1507,7 +1507,7 @@ class Session(_SessionClassMethods):
                     if cls in self.__binds:
                         return self.__binds[cls]
                 if clause is None:
-                    clause = mapper.mapped_table
+                    clause = mapper.persist_selectable
 
             if clause is not None:
                 for t in sql_util.find_tables(clause, include_crud=True):
@@ -1520,8 +1520,8 @@ class Session(_SessionClassMethods):
         if isinstance(clause, sql.expression.ClauseElement) and clause.bind:
             return clause.bind
 
-        if mapper and mapper.mapped_table.bind:
-            return mapper.mapped_table.bind
+        if mapper and mapper.persist_selectable.bind:
+            return mapper.persist_selectable.bind
 
         context = []
         if mapper is not None: