- An informative error message is raised if a Column

which has not yet been assigned a name, i.e. as in
declarative, is used in a context where it is
exported to the columns collection of an enclosing
select() construct, or if any construct involving
that column is compiled before its name is
assigned.  [ticket:1862]

2 files changed, 15 insertions, 9 deletions

diff --git a/lib/sqlalchemy/sql/compiler.py b/lib/sqlalchemy/sql/compiler.py
index fcff5e355..e47db7e28 100644
--- a/lib/sqlalchemy/sql/compiler.py
+++ b/lib/sqlalchemy/sql/compiler.py
@@ -332,6 +332,10 @@ class SQLCompiler(engine.Compiled):
             
     def visit_column(self, column, result_map=None, **kwargs):
         name = column.name
+        if name is None:
+            raise exc.CompileError("Cannot compile Column object until "
+                                   "it's 'name' is assigned.")
+            
         if not column.is_literal and isinstance(name, sql._generated_label):
             name = self._truncated_identifier("colident", name)
 
diff --git a/lib/sqlalchemy/sql/expression.py b/lib/sqlalchemy/sql/expression.py
index 1b1cfee8a..70d5f13fc 100644
--- a/lib/sqlalchemy/sql/expression.py
+++ b/lib/sqlalchemy/sql/expression.py
@@ -1852,17 +1852,19 @@ class ColumnElement(ClauseElement, _CompareMixin):
         descending selectable.
 
         """
-
-        if name:
-            co = ColumnClause(name, selectable, type_=getattr(self,
-                              'type', None))
+        if name is None:
+            name = self.anon_label
+            # TODO: may want to change this to anon_label,
+            # or some value that is more useful than the
+            # compiled form of the expression
+            key = str(self)
         else:
-            name = str(self)
-            co = ColumnClause(self.anon_label, selectable,
-                              type_=getattr(self, 'type', None))
-        
+            key = name
+            
+        co = ColumnClause(name, selectable, type_=getattr(self,
+                          'type', None))
         co.proxies = [self]
-        selectable.columns[name] = co
+        selectable.columns[key] = co
         return co
 
     def compare(self, other, use_proxies=False, equivalents=None, **kw):