- applying some refined versions of the ideas in the smarter_polymorphic

branch
- slowly moving Query towards a central "aliasing" paradigm which merges
the aliasing of polymorphic mappers to aliasing against arbitrary select_from(),
to the eventual goal of polymorphic mappers which can also eagerload other
relations
- supports many more join() scenarios involving polymorphic mappers in
most configurations
- PropertyAliasedClauses doesn't need "path", EagerLoader doesn't need to
guess about "towrap"

1 files changed, 19 insertions, 0 deletions

diff --git a/lib/sqlalchemy/sql/util.py b/lib/sqlalchemy/sql/util.py
index b45c0425c..c2ac26557 100644
--- a/lib/sqlalchemy/sql/util.py
+++ b/lib/sqlalchemy/sql/util.py
@@ -186,6 +186,25 @@ class ClauseAdapter(AbstractClauseProcessor):
         self.exclude = exclude
         self.equivalents = equivalents
 
+    def copy_and_chain(self, adapter):
+        """create a copy of this adapter and chain to the given adapter.
+        
+        currently this adapter must be unchained to start, raises
+        an exception if it's already chained.  
+        
+        Does not modify the given adapter.
+        """
+        
+        if adapter is None:
+            return self
+            
+        if hasattr(self, '_next_acp') or hasattr(self, '_next'):
+            raise NotImplementedError("Can't chain_to on an already chained ClauseAdapter (yet)")
+            
+        ca = ClauseAdapter(self.selectable, self.include, self.exclude, self.equivalents)
+        ca._next_acp = adapter
+        return ca
+        
     def convert_element(self, col):
         if isinstance(col, expression.FromClause):
             if self.selectable.is_derived_from(col):