Improve rendering of core statements w/ ORM elements

This patch contains a variety of ORM and expression layer
tweaks to support ORM constructs in select() statements,
without the 1.3.x requiremnt in Query that a full
_compile_context() + new select() is needed in order to
get a working statement object.

Includes such tweaks as the ability to implement
aliased class of an aliased class,
as we are looking to fully support ACs against subqueries,
as well as the ability to access anonymously-labeled
ColumnProperty expressions within subqueries by
naming the ".key" of the label after the property
key.   Some tuning to query.join() as well
as ORMJoin internals to allow things to work more
smoothly.

Change-Id: Id810f485c5f7ed971529489b84694e02a3356d6d

1 files changed, 31 insertions, 1 deletions

diff --git a/lib/sqlalchemy/sql/base.py b/lib/sqlalchemy/sql/base.py
index 6415d4b37..f14319089 100644
--- a/lib/sqlalchemy/sql/base.py
+++ b/lib/sqlalchemy/sql/base.py
@@ -522,7 +522,12 @@ class _MetaOptions(type):
 
     def __init__(cls, classname, bases, dict_):
         cls._cache_attrs = tuple(
-            sorted(d for d in dict_ if not d.startswith("__"))
+            sorted(
+                d
+                for d in dict_
+                if not d.startswith("__")
+                and d not in ("_cache_key_traversal",)
+            )
         )
         type.__init__(cls, classname, bases, dict_)
 
@@ -561,6 +566,31 @@ class Options(util.with_metaclass(_MetaOptions)):
     def _state_dict(cls):
         return cls._state_dict_const
 
+    @classmethod
+    def safe_merge(cls, other):
+        d = other._state_dict()
+
+        # only support a merge with another object of our class
+        # and which does not have attrs that we dont.   otherwise
+        # we risk having state that might not be part of our cache
+        # key strategy
+
+        if (
+            cls is not other.__class__
+            and other._cache_attrs
+            and set(other._cache_attrs).difference(cls._cache_attrs)
+        ):
+            raise TypeError(
+                "other element %r is not empty, is not of type %s, "
+                "and contains attributes not covered here %r"
+                % (
+                    other,
+                    cls,
+                    set(other._cache_attrs).difference(cls._cache_attrs),
+                )
+            )
+        return cls + d
+
 
 class CacheableOptions(Options, HasCacheKey):
     @hybridmethod