Fixed bug where the expression system relied upon the ``str()``

form of a some expressions when referring to the ``.c`` collection
on a ``select()`` construct, but the ``str()`` form isn't available
since the element relies on dialect-specific compilation constructs,
notably the ``__getitem__()`` operator as used with a Postgresql
``ARRAY`` element.  The fix also adds a new exception class
:class:`.UnsupportedCompilationError` which is raised in those cases
where a compiler is asked to compile something it doesn't know
how to.  Also in 0.8.3.
[ticket:2780]

1 files changed, 4 insertions, 1 deletions

diff --git a/lib/sqlalchemy/sql/expression.py b/lib/sqlalchemy/sql/expression.py
index 6ee110e9c..9e5c4cfcb 100644
--- a/lib/sqlalchemy/sql/expression.py
+++ b/lib/sqlalchemy/sql/expression.py
@@ -2360,7 +2360,10 @@ class ColumnElement(ClauseElement, ColumnOperators):
         """
         if name is None:
             name = self.anon_label
-            key = str(self)
+            try:
+                key = str(self)
+            except exc.UnsupportedCompilationError:
+                key = self.anon_label
         else:
             key = name
         co = ColumnClause(_as_truncated(name) if name_is_truncatable else name,