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, 28 insertions, 0 deletions

diff --git a/lib/sqlalchemy/orm/mapper.py b/lib/sqlalchemy/orm/mapper.py
index 7bfe70c36..4166e6d2a 100644
--- a/lib/sqlalchemy/orm/mapper.py
+++ b/lib/sqlalchemy/orm/mapper.py
@@ -1743,6 +1743,11 @@ class Mapper(
                     or prop.columns[0] is self.polymorphic_on
                 )
 
+            if isinstance(col, expression.Label):
+                # new in 1.4, get column property against expressions
+                # to be addressable in subqueries
+                col.key = col._key_label = key
+
             self.columns.add(col, key)
             for col in prop.columns + prop._orig_columns:
                 for col in col.proxy_set:
@@ -2282,6 +2287,29 @@ class Mapper(
             )
         )
 
+    def _columns_plus_keys(self, polymorphic_mappers=()):
+        if polymorphic_mappers:
+            poly_properties = self._iterate_polymorphic_properties(
+                polymorphic_mappers
+            )
+        else:
+            poly_properties = self._polymorphic_properties
+
+        return [
+            (prop.key, prop.columns[0])
+            for prop in poly_properties
+            if isinstance(prop, properties.ColumnProperty)
+        ]
+
+    @HasMemoized.memoized_attribute
+    def _polymorphic_adapter(self):
+        if self.with_polymorphic:
+            return sql_util.ColumnAdapter(
+                self.selectable, equivalents=self._equivalent_columns
+            )
+        else:
+            return None
+
     def _iterate_polymorphic_properties(self, mappers=None):
         """Return an iterator of MapperProperty objects which will render into
         a SELECT."""