模型已包含属性“触发器”。跳过装订

Question

我想为我的Order模型实现状态机，我正在使用这个漂亮的pytransitions库。但我面临着这个奇怪的问题

这是我的order.py模型：

from order_state_machine import OrderStateMachine

class Order(BaseModel):
    def __init__(self, order_dict):
        super().__init__(order_dict)
        # next line basically creates Customer object inside Order model
        self.set('customer', Customer(order_dict['customer']))
        self.machine = OrderStateMachine(self)

这是我的order_state_machine.py：

from transitions import Machine

class OrderStateMachine(Machine):
    order_states = ['pending', 'paid', 'shipped', 'delivered', 'canceled']

    order_transitions = [
        {'trigger': 'pay', 'source': 'pending', 'dest': 'paid'},
        {'trigger': 'deliver', 'source': 'shipped', 'dest': 'delivered'},
        {'trigger': 'cancel', 'source': 'shipped', 'dest': 'canceled'},
    ]

    def __init__(self, order):
        super().__init__(
            model=order,
            states=OrderStateMachine.order_states,
            transitions=OrderStateMachine.order_transitions,
            initial='pending'
        )

当我这样做的时候：

from order import Order

new_order = Order(order_dict)

new_order.state  # returns 'pending'
new_order.pay()
new_order.state  # I expect 'paid'

它，new_order.pay()行，给我TypeError: 'NoneType' object is not callable错误。还有一个Model already contains an attribute 'trigger'. Skip binding.警告，还有很多这样的警告

谁能帮我解决这个问题，可能是图书馆的维护人员。谢谢

Answer 1

我不能百分之百肯定地说，但是我假设您的BaseModel已经包含了属性和方法，这些属性和方法与transitions想要动态地修饰您的模型的方法重叠

transitions将执行“选中”赋值，这意味着当现有属性或方法尚未使用所需名称时，它将仅向模型分配触发器和便利函数。这背后的原因是，有时人们并不关心触发器，只按其名称调用函数（实际上使用trigger方法）

我假设您的BaseModel包含一个类似于[1]的属性赋值，如下所示

from transitions import Machine
import logging


class BaseModel:

    def __init__(self, order_dict):
        self.pay = None  # [1] already defined attribute

    def trigger(self):  # [2] already defined method
        pass


class OrderStateMachine(Machine):
    order_states = ['pending', 'paid', 'shipped', 'delivered', 'canceled']

    order_transitions = [
        {'trigger': 'pay', 'source': 'pending', 'dest': 'paid'},
        {'trigger': 'deliver', 'source': 'shipped', 'dest': 'delivered'},
        {'trigger': 'cancel', 'source': 'shipped', 'dest': 'canceled'},
    ]

    def __init__(self, order):
        super().__init__(
            model=order,
            states=OrderStateMachine.order_states,
            transitions=OrderStateMachine.order_transitions,
            initial='pending'
        )


class Order(BaseModel):
    def __init__(self, order_dict):
        super().__init__(order_dict)
        self.machine = OrderStateMachine(self)

logging.basicConfig(level=logging.DEBUG)
# [2] will cause 'Model already contains an attribute 'trigger'. Skip binding.'
new_order = Order({})  
new_order.state  # returns 'pending'
# [1] will cause a TypeError: 'NoneType' object is not callable
new_order.pay()
new_order.state

要解决这个问题，您应该确保触发器名称和模型属性是互斥的，以防止命名冲突。如果您确实定义了所有这些方法，例如将一些代码完成提示放到IDE中，并且您确实希望这样做，那么您可以重写Machine._checked_assignment方法：

class OveriddingMachine(Machine):

    # assign everything to the model ignoring already existing attributes
    def _checked_assignment(self, model, name, func):
        setattr(model, name, func)

请注意，如果您这样做，您的机器可能会以不希望的方式弄乱您的模型