--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/cubicweb/misc/scripts/migration_helper.py	Wed Jan 14 13:35:22 2015 +0100
@@ -0,0 +1,72 @@
+# copyright 2014 LOGILAB S.A. (Paris, FRANCE), all rights reserved.
+# contact http://www.logilab.fr/ -- mailto:contact@logilab.fr
+#
+# This file is part of CubicWeb.
+#
+# CubicWeb is free software: you can redistribute it and/or modify it under the
+# terms of the GNU Lesser General Public License as published by the Free
+# Software Foundation, either version 2.1 of the License, or (at your option)
+# any later version.
+#
+# CubicWeb is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+# FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Lesser General Public License along
+# with CubicWeb.  If not, see <http://www.gnu.org/licenses/>.
+
+"""Helper functions for migrations that aren't reliable enough or too dangerous
+to be available in the standard migration environment
+"""
+from __future__ import print_function
+
+__docformat__ = "restructuredtext en"
+
+def drop_entity_types_fast(*etypes, **kwargs):
+    """drop an entity type bypassing all hooks
+
+    here be dragons.
+    """
+    # XXX cascade deletion through composite relations?
+
+    for etype in etypes:
+
+        if etype not in schema:
+            print('%s does not exist' % etype)
+            continue
+        etype = schema[etype]
+
+        # ignore attributes and inlined rels since they'll be dropped anyway
+        srels = [x.type for x in etype.subject_relations() if x.eid and not (x.final or x.inlined)]
+
+        orels = [x.type for x in etype.object_relations() if x.eid and not x.inlined]
+        inlined_rels = [x for x in etype.object_relations() if x.eid and x.inlined]
+
+        # eids to be deleted could be listed in some other entity tables through inlined relations
+        for rtype in inlined_rels:
+            for subjtype in rtype.subjects(etype):
+                if subjtype in etypes:
+                    continue
+                sql('UPDATE cw_%(stype)s SET cw_%(rtype)s = NULL '
+                    'WHERE cw_%(rtype)s IN (SELECT eid FROM entities WHERE type = %%s)' %
+                    {'stype': subjtype.type, 'rtype': rtype.type},
+                    (etype.type,))
+
+        for rel in srels:
+            if all(subj in etypes for subj in rel.subjects()) or all(obj in etypes for obj in rel.objects()):
+                sql('DELETE FROM %s_relation' % rel.type)
+            else:
+                sql('DELETE FROM %s_relation WHERE eid_from IN (SELECT eid FROM entities WHERE type = %%s)' % rel.type, (etype.type,))
+        for rel in orels:
+            if all(subj in etypes for subj in rel.subjects()) or all(obj in etypes for obj in rel.objects()):
+                sql('DELETE FROM %s_relation' % rel.type)
+            else:
+                sql('DELETE FROM %s_relation WHERE eid_to IN (SELECT eid FROM entities WHERE type = %%s)' % rel, (etype.type,))
+
+        sql('DELETE FROM appears WHERE uid IN (SELECT eid FROM entities WHERE type = %s)', (etype.type,))
+        sql('DELETE FROM cw_%s' % etype.type)
+        sql('DELETE FROM entities WHERE type = %s', (etype.type,))
+
+    for etype in etypes:
+        drop_entity_type(etype, **kwargs)