categories_string = fields.Function(fields.Char('Categories'
#, order_field='partys.get_categories_string %(order)s, partys.name %(order)s'#FIXME enable ordering in tree
), 'get_categories_string', searcher='search_categories_string')

    def get_categories_string(self, ids, name):
        if not ids:
            return []
        res = {}
        for party in self.browse(ids):
            res[party.id] = ', '.join(sorted(cat.rec_name for cat in party.categories))
        return res

    def search_categories_string(self, name, clause):
        ids = self.search([('name', '!=', '')], order=[])#FIXME optimise this
        res = []
        value = clause[2]
        cats = self.get_categories_string(ids, name)
        for cat in cats.keys():
            if value.lower() in cats[cat].lower():
                res.append('categories', '=', cats[cat])
        res.append(('categories', clause[1], value))
        return res