Simplify _ColumnEntity, related

In the interests of making Query much more lightweight up front,
rework the calculations done at the top when the entities
are constructed to be much less inolved.  Use the new
coercion system for _ColumnEntity and stop accepting
plain strings, this will need to emit a deprecation warning
in 1.3.x.     Use annotations and other techniques to reduce
the decisionmaking and complexity of Query.

For the use case of subquery(), .statement, etc. we would like
to do minimal work in order to get the columns clause.

Change-Id: I7e459bbd3bb10ec71235f75ef4f3b0a969bec590

1 files changed, 10 insertions, 10 deletions

diff --git a/lib/sqlalchemy/orm/attributes.py b/lib/sqlalchemy/orm/attributes.py
index 9d404e00d..117dd4cea 100644
--- a/lib/sqlalchemy/orm/attributes.py
+++ b/lib/sqlalchemy/orm/attributes.py
@@ -168,18 +168,18 @@ class QueryableAttribute(
         """
         return inspection.inspect(self._parententity)
 
-    @property
+    @util.memoized_property
     def expression(self):
-        return self.comparator.__clause_element__()
-
-    def __clause_element__(self):
-        return self.comparator.__clause_element__()
+        return self.comparator.__clause_element__()._annotate(
+            {"orm_key": self.key}
+        )
 
-    def _query_clause_element(self):
-        """like __clause_element__(), but called specifically
-        by :class:`.Query` to allow special behavior."""
+    @property
+    def _annotations(self):
+        return self.__clause_element__()._annotations
 
-        return self.comparator._query_clause_element()
+    def __clause_element__(self):
+        return self.expression
 
     def _bulk_update_tuples(self, value):
         """Return setter tuples for a bulk UPDATE."""
@@ -207,7 +207,7 @@ class QueryableAttribute(
         )
 
     def label(self, name):
-        return self._query_clause_element().label(name)
+        return self.__clause_element__().label(name)
 
     def operate(self, op, *other, **kwargs):
         return op(self.comparator, *other, **kwargs)