1 files changed, 48 insertions, 0 deletions
diff --git a/lib/sqlalchemy/sql_util.py b/lib/sqlalchemy/sql_util.py
index bfbcff554..4c6cd4d07 100644
--- a/lib/sqlalchemy/sql_util.py
+++ b/lib/sqlalchemy/sql_util.py
@@ -107,3 +107,51 @@ class Aliasizer(sql.ClauseVisitor):
             binary.left = self.get_alias(binary.left.table).corresponding_column(binary.left)
         if isinstance(binary.right, schema.Column) and self.tables.has_key(binary.right.table):
             binary.right = self.get_alias(binary.right.table).corresponding_column(binary.right)
+
+
+class ClauseAdapter(sql.ClauseVisitor):
+    """given a clause (like as in a WHERE criterion), locates columns which 'correspond' to a given selectable, 
+    and changes those columns to be that of the selectable.
+    
+        such as:
+        
+        table1 = Table('sometable', metadata, 
+            Column('col1', Integer),
+            Column('col2', Integer)
+            )
+        table2 = Table('someothertable', metadata, 
+            Column('col1', Integer),
+            Column('col2', Integer)
+            )
+    
+        condition = table1.c.col1 == table2.c.col1
+        
+        and make an alias of table1:
+        
+        s = table1.alias('foo')
+        
+        calling condition.accept_visitor(ClauseAdapter(s)) converts condition to read:
+        
+        s.c.col1 == table2.c.col1
+    
+    """
+    def __init__(self, selectable):
+        self.selectable = selectable
+    def visit_binary(self, binary):
+        if isinstance(binary.left, sql.ColumnElement):
+            col = self.selectable.corresponding_column(binary.left, raiseerr=False, keys_ok=False)
+            if col is not None:
+                binary.left = col
+        if isinstance(binary.right, sql.ColumnElement):
+            col = self.selectable.corresponding_column(binary.right, raiseerr=False, keys_ok=False)
+            if col is not None:
+                binary.right = col
+
+class ColumnsInClause(sql.ClauseVisitor):
+    """given a selectable, visits clauses and determines if any columns from the clause are in the selectable"""
+    def __init__(self, selectable):
+        self.selectable = selectable
+        self.result = False
+    def visit_column(self, column):
+        if self.selectable.c.get(column.key) is column:
+            self.result = True