diff -r 058bb3dc685f -r 0b59724cb3f2 cubicweb/misc/migration/3.21.0_Any.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/cubicweb/misc/migration/3.21.0_Any.py	Sat Jan 16 13:48:51 2016 +0100
@@ -0,0 +1,174 @@
+from __future__ import print_function
+
+from cubicweb.schema import PURE_VIRTUAL_RTYPES
+from cubicweb.server.schema2sql import rschema_has_table
+
+
+def add_foreign_keys():
+    source = repo.system_source
+    if not source.dbhelper.alter_column_support:
+        return
+    for rschema in schema.relations():
+        if rschema.inlined:
+            add_foreign_keys_inlined(rschema)
+        elif rschema_has_table(rschema, skip_relations=PURE_VIRTUAL_RTYPES):
+            add_foreign_keys_relation(rschema)
+    for eschema in schema.entities():
+        if eschema.final:
+            continue
+        add_foreign_key_etype(eschema)
+
+
+def add_foreign_keys_relation(rschema):
+    args = {'r': rschema.type}
+    count = sql('SELECT COUNT(*) FROM ('
+                '    SELECT eid_from FROM %(r)s_relation'
+                '  UNION'
+                '    SELECT eid_to FROM %(r)s_relation'
+                '  EXCEPT'
+                '    SELECT eid FROM entities) AS eids' % args,
+                ask_confirm=False)[0][0]
+    if count:
+        print('%s references %d unknown entities, deleting' % (rschema, count))
+        sql('DELETE FROM %(r)s_relation '
+            'WHERE eid_from IN (SELECT eid_from FROM %(r)s_relation EXCEPT SELECT eid FROM entities)' % args)
+        sql('DELETE FROM %(r)s_relation '
+            'WHERE eid_to IN (SELECT eid_to FROM %(r)s_relation EXCEPT SELECT eid FROM entities)' % args)
+
+    args['from_fk'] = '%(r)s_relation_eid_from_fkey' % args
+    args['to_fk'] = '%(r)s_relation_eid_to_fkey' % args
+    args['table'] = '%(r)s_relation' % args
+    if repo.system_source.dbdriver == 'postgres':
+        sql('ALTER TABLE %(table)s DROP CONSTRAINT IF EXISTS %(from_fk)s' % args,
+            ask_confirm=False)
+        sql('ALTER TABLE %(table)s DROP CONSTRAINT IF EXISTS %(to_fk)s' % args,
+            ask_confirm=False)
+    elif repo.system_source.dbdriver.startswith('sqlserver'):
+        sql("IF OBJECT_ID('%(from_fk)s', 'F') IS NOT NULL "
+            "ALTER TABLE %(table)s DROP CONSTRAINT %(from_fk)s" % args,
+            ask_confirm=False)
+        sql("IF OBJECT_ID('%(to_fk)s', 'F') IS NOT NULL "
+            "ALTER TABLE %(table)s DROP CONSTRAINT %(to_fk)s" % args,
+            ask_confirm=False)
+    sql('ALTER TABLE %(table)s ADD CONSTRAINT %(from_fk)s '
+        'FOREIGN KEY (eid_from) REFERENCES entities (eid)' % args,
+        ask_confirm=False)
+    sql('ALTER TABLE %(table)s ADD CONSTRAINT %(to_fk)s '
+        'FOREIGN KEY (eid_to) REFERENCES entities (eid)' % args,
+        ask_confirm=False)
+
+
+def add_foreign_keys_inlined(rschema):
+    for eschema in rschema.subjects():
+        args = {'e': eschema.type, 'r': rschema.type}
+        args['c'] = 'cw_%(e)s_cw_%(r)s_fkey' % args
+
+        if eschema.rdef(rschema).cardinality[0] == '1':
+            broken_eids = sql('SELECT cw_eid FROM cw_%(e)s WHERE cw_%(r)s IS NULL' % args,
+                              ask_confirm=False)
+            if broken_eids:
+                print('Required relation %(e)s.%(r)s missing' % args)
+                args['eids'] = ', '.join(str(eid) for eid, in broken_eids)
+                rql('DELETE %(e)s X WHERE X eid IN (%(eids)s)' % args)
+            broken_eids = sql('SELECT cw_eid FROM cw_%(e)s WHERE cw_%(r)s IN (SELECT cw_%(r)s FROM cw_%(e)s '
+                              'EXCEPT SELECT eid FROM entities)' % args,
+                              ask_confirm=False)
+            if broken_eids:
+                print('Required relation %(e)s.%(r)s references unknown objects, deleting subject entities' % args)
+                args['eids'] = ', '.join(str(eid) for eid, in broken_eids)
+                rql('DELETE %(e)s X WHERE X eid IN (%(eids)s)' % args)
+        else:
+            if sql('SELECT COUNT(*) FROM ('
+                   '    SELECT cw_%(r)s FROM cw_%(e)s WHERE cw_%(r)s IS NOT NULL'
+                   '  EXCEPT'
+                   '    SELECT eid FROM entities) AS eids' % args,
+                   ask_confirm=False)[0][0]:
+                print('%(e)s.%(r)s references unknown entities, deleting relation' % args)
+                sql('UPDATE cw_%(e)s SET cw_%(r)s = NULL WHERE cw_%(r)s IS NOT NULL AND cw_%(r)s IN '
+                    '(SELECT cw_%(r)s FROM cw_%(e)s EXCEPT SELECT eid FROM entities)' % args)
+
+        if repo.system_source.dbdriver == 'postgres':
+            sql('ALTER TABLE cw_%(e)s DROP CONSTRAINT IF EXISTS %(c)s' % args,
+                ask_confirm=False)
+        elif repo.system_source.dbdriver.startswith('sqlserver'):
+            sql("IF OBJECT_ID('%(c)s', 'F') IS NOT NULL "
+                "ALTER TABLE cw_%(e)s DROP CONSTRAINT %(c)s" % args,
+                ask_confirm=False)
+        sql('ALTER TABLE cw_%(e)s ADD CONSTRAINT %(c)s '
+            'FOREIGN KEY (cw_%(r)s) references entities(eid)' % args,
+            ask_confirm=False)
+
+
+def add_foreign_key_etype(eschema):
+    args = {'e': eschema.type}
+    if sql('SELECT COUNT(*) FROM ('
+           '    SELECT cw_eid FROM cw_%(e)s'
+           '  EXCEPT'
+           '    SELECT eid FROM entities) AS eids' % args,
+           ask_confirm=False)[0][0]:
+        print('%(e)s has nonexistent entities, deleting' % args)
+        sql('DELETE FROM cw_%(e)s WHERE cw_eid IN '
+            '(SELECT cw_eid FROM cw_%(e)s EXCEPT SELECT eid FROM entities)' % args)
+    args['c'] = 'cw_%(e)s_cw_eid_fkey' % args
+    if repo.system_source.dbdriver == 'postgres':
+        sql('ALTER TABLE cw_%(e)s DROP CONSTRAINT IF EXISTS %(c)s' % args,
+            ask_confirm=False)
+    elif repo.system_source.dbdriver.startswith('sqlserver'):
+        sql("IF OBJECT_ID('%(c)s', 'F') IS NOT NULL "
+            "ALTER TABLE cw_%(e)s DROP CONSTRAINT %(c)s" % args,
+            ask_confirm=False)
+    sql('ALTER TABLE cw_%(e)s ADD CONSTRAINT %(c)s '
+        'FOREIGN KEY (cw_eid) REFERENCES entities (eid)' % args,
+        ask_confirm=False)
+
+
+add_foreign_keys()
+
+cu = session.cnxset.cu
+helper = repo.system_source.dbhelper
+
+helper.drop_index(cu, 'entities', 'extid', False)
+# don't use create_index because it doesn't work for columns that may be NULL
+# on sqlserver
+for query in helper.sqls_create_multicol_unique_index('entities', ['extid']):
+    cu.execute(query)
+
+if 'moved_entities' not in helper.list_tables(cu):
+    sql('''
+    CREATE TABLE moved_entities (
+      eid INTEGER PRIMARY KEY NOT NULL,
+      extid VARCHAR(256) UNIQUE
+    )
+    ''')
+
+moved_entities = sql('SELECT -eid, extid FROM entities WHERE eid < 0',
+                     ask_confirm=False)
+if moved_entities:
+    cu.executemany('INSERT INTO moved_entities (eid, extid) VALUES (%s, %s)',
+                   moved_entities)
+    sql('DELETE FROM entities WHERE eid < 0')
+
+commit()
+
+sync_schema_props_perms('CWEType')
+
+sync_schema_props_perms('cwuri')
+
+from cubicweb.server.schema2sql import check_constraint
+
+for cwconstraint in rql('Any C WHERE R constrained_by C').entities():
+    cwrdef = cwconstraint.reverse_constrained_by[0]
+    rdef = cwrdef.yams_schema()
+    cstr = rdef.constraint_by_eid(cwconstraint.eid)
+    if cstr.type() not in ('BoundaryConstraint', 'IntervalBoundConstraint', 'StaticVocabularyConstraint'):
+        continue
+    cstrname, check = check_constraint(rdef.subject, rdef.object, rdef.rtype.type,
+            cstr, helper, prefix='cw_')
+    args = {'e': rdef.subject.type, 'c': cstrname, 'v': check}
+    if repo.system_source.dbdriver == 'postgres':
+        sql('ALTER TABLE cw_%(e)s DROP CONSTRAINT IF EXISTS %(c)s' % args)
+    elif repo.system_source.dbdriver.startswith('sqlserver'):
+        sql("IF OBJECT_ID('%(c)s', 'C') IS NOT NULL "
+            "ALTER TABLE cw_%(e)s DROP CONSTRAINT %(c)s" % args)
+    sql('ALTER TABLE cw_%(e)s ADD CONSTRAINT %(c)s CHECK(%(v)s)' % args)
+commit()