--- 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):

--- a/entities/adapters.py	Mon May 18 19:47:34 2015 +0200
+++ b/entities/adapters.py	Sun Mar 22 23:27:13 2015 +0100
@@ -24,11 +24,13 @@
 
 from itertools import chain
 from warnings import warn
+from hashlib import md5
 
 from logilab.mtconverter import TransformError
 from logilab.common.decorators import cached
 
-from cubicweb import ValidationError, view
+from cubicweb import ValidationError, view, ViolatedConstraint
+from cubicweb.schema import CONSTRAINTS
 from cubicweb.predicates import is_instance, relation_possible, match_exception
 
 
@@ -372,3 +374,25 @@
             i18nvalues.append(rtype + '-rtype')
         errors[''] = _('some relations violate a unicity constraint')
         raise ValidationError(self.entity.eid, errors, msgargs=msgargs, i18nvalues=i18nvalues)
+
+
+class IUserFriendlyCheckConstraint(IUserFriendlyError):
+    __select__ = match_exception(ViolatedConstraint)
+
+    def raise_user_exception(self):
+        _ = self._cw._
+        cstrname = self.exc.cstrname
+        eschema = self.entity.e_schema
+        for rschema, attrschema in eschema.attribute_definitions():
+            rdef = rschema.rdef(eschema, attrschema)
+            for constraint in rdef.constraints:
+                if cstrname == 'cstr' + md5(eschema.type + rschema.type + constraint.type() + (constraint.serialize() or '')).hexdigest():
+                    break
+            else:
+                continue
+            break
+        else:
+            assert 0
+        key = rschema.type + '-subject'
+        msg, args = constraint.failed_message(key, self.entity.cw_edited[rschema.type])
+        raise ValidationError(self.entity.eid, {key: msg}, args)

--- a/server/repository.py	Mon May 18 19:47:34 2015 +0200
+++ b/server/repository.py	Sun Mar 22 23:27:13 2015 +0100
@@ -43,7 +43,7 @@
 from cubicweb import (CW_MIGRATION_MAP, QueryError,
                       UnknownEid, AuthenticationError, ExecutionError,
                       BadConnectionId, ValidationError,
-                      UniqueTogetherError, onevent)
+                      UniqueTogetherError, onevent, ViolatedConstraint)
 from cubicweb import cwvreg, schema, server
 from cubicweb.server import ShuttingDown, utils, hook, querier, sources
 from cubicweb.server.session import Session, InternalManager
@@ -927,7 +927,7 @@
         self.add_info(cnx, entity, source, extid)
         try:
             source.add_entity(cnx, entity)
-        except UniqueTogetherError as exc:
+        except (UniqueTogetherError, ViolatedConstraint) as exc:
             userhdlr = cnx.vreg['adapters'].select(
                 'IUserFriendlyError', cnx, entity=entity, exc=exc)
             userhdlr.raise_user_exception()
@@ -990,7 +990,7 @@
             try:
                 source.update_entity(cnx, entity)
                 edited.saved = True
-            except UniqueTogetherError as exc:
+            except (UniqueTogetherError, ViolatedConstraint) as exc:
                 userhdlr = cnx.vreg['adapters'].select(
                     'IUserFriendlyError', cnx, entity=entity, exc=exc)
                 userhdlr.raise_user_exception()

--- a/server/sources/native.py	Mon May 18 19:47:34 2015 +0200
+++ b/server/sources/native.py	Sun Mar 22 23:27:13 2015 +0100
@@ -46,7 +46,7 @@
 from yams.schema import role_name
 
 from cubicweb import (UnknownEid, AuthenticationError, ValidationError, Binary,
-                      UniqueTogetherError, UndoTransactionException)
+                      UniqueTogetherError, UndoTransactionException, ViolatedConstraint)
 from cubicweb import transaction as tx, server, neg_role
 from cubicweb.utils import QueryCache
 from cubicweb.schema import VIRTUAL_RTYPES
@@ -731,6 +731,18 @@
                         columns = arg.split(':', 1)[1].split(',')
                         rtypes = [c.split('.', 1)[1].strip()[3:] for c in columns]
                         raise UniqueTogetherError(cnx, rtypes=rtypes)
+
+                    mo = re.search('"cstr[a-f0-9]{32}"', arg)
+                    if mo is not None:
+                        # postgresql
+                        raise ViolatedConstraint(cnx, cstrname=mo.group(0)[1:-1])
+                    if arg.startswith('CHECK constraint failed:'):
+                        # sqlite3 (new)
+                        raise ViolatedConstraint(cnx, cstrname=arg.split(':', 1)[1].strip())
+                    mo = re.match('^constraint (cstr.*) failed$', arg)
+                    if mo is not None:
+                        # sqlite3 (old)
+                        raise ViolatedConstraint(cnx, cstrname=mo.group(1))
             raise
         return cursor
 

--- a/server/test/data/schema.py	Mon May 18 19:47:34 2015 +0200
+++ b/server/test/data/schema.py	Sun Mar 22 23:27:13 2015 +0100
@@ -89,7 +89,7 @@
 
 class Note(WorkflowableEntityType):
     date = String(maxsize=10)
-    type = String(maxsize=6)
+    type = String(vocabulary=[u'todo', u'a', u'b', u'T', u'lalala'])
     para = String(maxsize=512,
                   __permissions__ = {
                       'add': ('managers', ERQLExpression('X in_state S, S name "todo"')),

--- a/server/test/unittest_postgres.py	Mon May 18 19:47:34 2015 +0200
+++ b/server/test/unittest_postgres.py	Sun Mar 22 23:27:13 2015 +0100
@@ -22,6 +22,7 @@
 
 from logilab.common.testlib import SkipTest
 
+from cubicweb import ValidationError
 from cubicweb.devtools import PostgresApptestConfiguration, startpgcluster, stoppgcluster
 from cubicweb.devtools.testlib import CubicWebTC
 from cubicweb.predicates import is_instance
@@ -123,6 +124,18 @@
             self.assertEqual(datenaiss.tzinfo, None)
             self.assertEqual(datenaiss.utctimetuple()[:5], (1977, 6, 7, 2, 0))
 
+    def test_constraint_validationerror(self):
+        with self.admin_access.repo_cnx() as cnx:
+            with cnx.allow_all_hooks_but('integrity'):
+                with self.assertRaises(ValidationError) as cm:
+                    cnx.execute("INSERT Note N: N type 'nogood'")
+                self.assertEqual(cm.exception.errors,
+                        {'type-subject': u'invalid value %(KEY-value)s, it must be one of %(KEY-choices)s'})
+                self.assertEqual(cm.exception.msgargs,
+                        {'type-subject-value': u'"nogood"',
+                         'type-subject-choices': u'"todo", "a", "b", "T", "lalala"'})
+
+
 class PostgresLimitSizeTC(CubicWebTC):
     configcls = PostgresApptestConfiguration
 
@@ -141,6 +154,7 @@
             yield self.assertEqual, sql("SELECT limit_size('<span>a>b</span>', 'text/html', 2)"), \
                 'a>...'
 
+
 if __name__ == '__main__':
     from logilab.common.testlib import unittest_main
     unittest_main()