Don't use write for migration
In http://hg.tryton.org/modules/stock/file/07b42999efdb/shipment.py#l163
using self.write could generate error if some _constraint need some new field
not yet created.
In http://hg.tryton.org/modules/stock/file/07b42999efdb/shipment.py#l163
using self.write could generate error if some _constraint need some new field
not yet created.