删除order_line时出现Odoo / OpenERP完整性错误

Question

我使用委托从自定义模块中的sale_order继承字段：

class EXAMPLE(osv.osv):
_name = 'EXAMPLECLASS'

_inherits = {
    'sale.order': 'sale_order_id'}

我使用sale_order的标准视图。一切正常，我可以在sale_order中添加和更新order_lines。但是，当我尝试从sale_order删除order_line时，我收到以下错误：

Integrity Error
The operation cannot be completed, probably due to the following:
- deletion: you may be trying to delete a record while other records still reference it
- creation/update: a mandatory field is not correctly set
[object with reference: order_id - order.id]

我错过了什么？我认为这与“＆＃39; _inherits＆＃39;只继承字段而不是方法。

非常感谢任何有关此事的帮助。