memoize current options and joins w with_entities/with_only_cols

Fixed further regressions in the same area as that of :ticket:`6052` where
loader options as well as invocations of methods like
:meth:`_orm.Query.join` would fail if the left side of the statement for
which the option/join depends upon were replaced by using the
:meth:`_orm.Query.with_entities` method, or when using 2.0 style queries
when using the :meth:`_sql.Select.with_only_columns` method. A new set of
state has been added to the objects which tracks the "left" entities that
the options / join were made against which is memoized when the lead
entities are changed.

Fixes: #6503
Fixes: #6253
Change-Id: I211b2af98b0b20d1263fb15dc513884dcc5de6a4

1 files changed, 35 insertions, 0 deletions

diff --git a/lib/sqlalchemy/sql/visitors.py b/lib/sqlalchemy/sql/visitors.py
index 93ee8eb1c..c750c546a 100644
--- a/lib/sqlalchemy/sql/visitors.py
+++ b/lib/sqlalchemy/sql/visitors.py
@@ -24,6 +24,7 @@ http://techspot.zzzeek.org/2008/01/23/expression-transformations/ .
 """
 
 from collections import deque
+import itertools
 import operator
 
 from .. import exc
@@ -119,6 +120,38 @@ class Traversible(util.with_metaclass(TraversibleType)):
 
     """
 
+    @util.preload_module("sqlalchemy.sql.traversals")
+    def get_children(self, omit_attrs=(), **kw):
+        r"""Return immediate child :class:`.visitors.Traversible`
+        elements of this :class:`.visitors.Traversible`.
+
+        This is used for visit traversal.
+
+        \**kw may contain flags that change the collection that is
+        returned, for example to return a subset of items in order to
+        cut down on larger traversals, or to return child items from a
+        different context (such as schema-level collections instead of
+        clause-level).
+
+        """
+
+        traversals = util.preloaded.sql_traversals
+
+        try:
+            traverse_internals = self._traverse_internals
+        except AttributeError:
+            # user-defined classes may not have a _traverse_internals
+            return []
+
+        dispatch = traversals._get_children.run_generated_dispatch
+        return itertools.chain.from_iterable(
+            meth(obj, **kw)
+            for attrname, obj, meth in dispatch(
+                self, traverse_internals, "_generated_get_children_traversal"
+            )
+            if attrname not in omit_attrs and obj is not None
+        )
+
 
 class _InternalTraversalType(type):
     def __init__(cls, clsname, bases, clsdict):
@@ -393,6 +426,8 @@ class InternalTraversal(util.with_metaclass(_InternalTraversalType, object)):
 
     dp_setup_join_tuple = symbol("SJ")
 
+    dp_memoized_select_entities = symbol("ME")
+
     dp_statement_hint_list = symbol("SH")
     """Visit the ``_statement_hints`` collection of a
     :class:`_expression.Select`