diff -r 8a4175557426 -r c5eed908117d misc/migration/3.18.0_Any.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/misc/migration/3.18.0_Any.py	Fri Aug 23 15:06:27 2013 +0200
@@ -0,0 +1,60 @@
+sync_schema_props_perms('defaultval')
+
+def convert_defaultval(cwattr, default):
+    from decimal import Decimal
+    import yams
+    from cubicweb import Binary
+    if default is None:
+        return
+    atype = cwattr.to_entity[0].name
+    if atype == 'Boolean':
+        assert default in ('True', 'False'), default
+        default = default == 'True'
+    elif atype in ('Int', 'BigInt'):
+        default = int(default)
+    elif atype == 'Float':
+        default = float(default)
+    elif atype == 'Decimal':
+        default = Decimal(default)
+    elif atype in ('Date', 'Datetime', 'TZDatetime', 'Time'):
+        try:
+            # handle NOW and TODAY, keep them stored as strings
+            yams.KEYWORD_MAP[atype][default.upper()]
+            default = default.upper()
+        except KeyError:
+            # otherwise get an actual date or datetime
+            default = yams.DATE_FACTORY_MAP[atype](default)
+    else:
+        assert atype == 'String', atype
+        default = unicode(default)
+    return Binary.zpickle(default)
+
+dbh = repo.system_source.dbhelper
+driver = config.sources()['system']['db-driver']
+if driver == 'postgres' or driver.startswith('sqlserver'):
+    sql('ALTER TABLE cw_cwattribute ADD new_defaultval %s' % dbh.TYPE_MAPPING['Bytes'])
+else:
+    assert False, 'upgrade not supported on this database backend'
+
+for cwattr in rql('CWAttribute X').entities():
+    olddefault = cwattr.defaultval
+    if olddefault is not None:
+        req = "UPDATE cw_cwattribute SET new_defaultval = %(val)s WHERE cw_eid = %(eid)s"
+        args = {'val': dbh.binary_value(convert_defaultval(cwattr, olddefault).getvalue()), 'eid': cwattr.eid}
+        sql(req, args, ask_confirm=False)
+
+sql('ALTER TABLE cw_cwattribute DROP COLUMN cw_defaultval')
+if config.sources()['system']['db-driver'] == 'postgres':
+    sql('ALTER TABLE cw_cwattribute RENAME COLUMN new_defaultval TO cw_defaultval')
+else:
+    sql("sp_rename 'cw_cwattribute.new_defaultval', 'cw_defaultval', 'COLUMN'")
+
+# Set object type to "Bytes" for CWAttribute's "defaultval" attribute
+rql('SET X to_entity B WHERE X is CWAttribute, X from_entity Y, Y name "CWAttribute", '
+    'X relation_type Z, Z name "defaultval", B name "Bytes"')
+
+from yams import buildobjs as ybo
+schema.add_relation_def(ybo.RelationDefinition('CWAttribute', 'defaultval', 'Bytes'))
+schema.del_relation_def('CWAttribute', 'defaultval', 'String')
+
+commit()