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, 12 insertions, 0 deletions

diff --git a/lib/sqlalchemy/exc.py b/lib/sqlalchemy/exc.py
index f5dc1119d..cfd1e2bc7 100644
--- a/lib/sqlalchemy/exc.py
+++ b/lib/sqlalchemy/exc.py
@@ -72,6 +72,18 @@ class CircularDependencyError(SQLAlchemyError):
 class CompileError(SQLAlchemyError):
     """Raised when an error occurs during SQL compilation"""
 
+class UnsupportedCompilationError(CompileError):
+    """Raised when an operation is not supported by the given compiler.
+
+
+    .. versionadded:: 0.8.3
+
+    """
+
+    def __init__(self, compiler, element_type):
+        super(UnsupportedCompilationError, self).__init__(
+                    "Compiler %r can't render element of type %s" %
+                                (compiler, element_type))
 
 class IdentifierError(SQLAlchemyError):
     """Raised when a schema name is beyond the max character limit"""