如何在odoo8中设置Integer的最小和最大验证？

_columns = {
    'product_id': fields.many2one('ims.product', 'Product', required=True),
    'qty' : fields.integer('Qty', required=True),
    'cost': fields.float('Product Cost',digits=(12,2), required=True),
    'total_cost': fields.float('Total Cost', digits=(12,2), required=True)
}
_columns = {
    'product_id': fields.many2one(