diff -r f1773842077d -r 1e6655cff5ab _exceptions.py
--- a/_exceptions.py	Mon May 18 19:47:34 2015 +0200
+++ b/_exceptions.py	Sun Mar 22 23:27:13 2015 +0100
@@ -102,6 +102,12 @@
         return None, self.rtypes
 
 
+class ViolatedConstraint(RepositoryError):
+    def __init__(self, cnx, cstrname):
+        self.cnx = cnx
+        self.cstrname = cstrname
+
+
 # security exceptions #########################################################
 
 class Unauthorized(SecurityError):