Question

让我们说我有以下节点：

perform_disk_size_change = ( 
    flow.Handler(
        this.perform_proxmox_api_request
    ).Next(this.notify_iaas_success)
)

如果perform_proxmox_api_request引发异常怎么办？我可以指定一个Exception节点，以便将任何异常都转到该节点吗？

perform_disk_size_change = ( 
    flow.Handler(
        this.perform_proxmox_api_request
    ).Next(this.notify_iaas_success).Except(this.notify_iaas_fail)
)

Answer 1

所以我想出了以下解决方案，不能完全确定是否应该以这种方式完成，问题是HandlerActivation立即执行，因此没有给我机会将异常对象传递给下一个激活（如果是处理程序节点），我仍然不知道如何在无需使用另一个自定义节点的情况下将异常传递给下一次激活。

from copy import copy
from viewflow.activation import Activation, STATUS, all_leading_canceled
from viewflow.nodes.handler import HandlerActivation
from viewflow.rest import flow


class HandlerActivationCatchExcept(HandlerActivation):
    def __init__(self, *args, **kwargs):
        self.caught_exception = None
        super(HandlerActivationCatchExcept, self).__init__(*args, **kwargs)

    def execute(self):
        """Run the callback."""
        try:
            self.flow_task.handler(self)
        except Exception as ex:
            self.caught_exception = ex

    @Activation.status.transition(source=STATUS.DONE, conditions=[all_leading_canceled])
    def activate_next(self):
        """Activate all outgoing edges."""
        if self.caught_exception:
            for mapping in self.flow_task.exception_mappings:
                if isinstance(self.caught_exception, mapping['cls']):
                    mapping['node'].activate(prev_activation=self, token=self.task.token)
        else:
            super(HandlerActivationCatchExcept, self).activate_next()


class CatchExceptionHandler(flow.Handler):
    """
    Custom handler node to allow catching exception and route to certain node
    usage: CatchExceptionHandler(method).Except(default_node)
           CatchExceptionHandler(method).Except(specific_node, SpecificExceptionCls).Except(default_node)
    """

    activation_class = HandlerActivationCatchExcept

    def __init__(self, *args, **kwargs):
        super(HandlerCatchExcept, self).__init__(*args, **kwargs)
        self.exception_mappings = []

    def _resolve(self, resolver):
        super(HandlerCatchExcept, self)._resolve(resolver)
        for exception_mapping in self.exception_mappings:
            exception_mapping['node'] = resolver.get_implementation(exception_mapping['node'])

    def _outgoing(self):
        if self._next:
            yield Edge(src=self, dst=self._next, edge_class='next')
        # not sure what edge_class to use for exception in diagram
        for exception_mapping in self.exception_mappings:
            yield Edge(src=self, dst=exception_mapping['node'], edge_class='next')

    def Except(self, node, exception_cls=Exception):
        self.exception_mappings.append({"cls": exception_cls, "node": node})
        return copy(self)


class HandleExceptionActivation(HandlerActivation):
    @classmethod
    def activate(cls, flow_task, prev_activation, token):
        """Instantiate new task."""
        task = flow_task.flow_class.task_class(
            process=prev_activation.process,
            flow_task=flow_task,
            token=token)

        task.save()
        task.previous.add(prev_activation.task)

        activation = cls()
        # adds previous activation ref
        activation.prev_activation = prev_activation
        activation.initialize(flow_task, task)
        activation.perform()

        return activation


class ExceptionHandler(flow.Handler):
    activation_class = HandleExceptionActivation

用法如下：

perform_disk_size_change = (
    nodes.CatchExceptionHandler(
        this.perform_proxmox_api_request
    ).Next(
        this.notify_iaas_success
    ).Except(
        this.notify_iaas_team, TechnicalExceptionCls
    ).Except(
        this.notify_customer_failed
    )
)

notify_iaas_team = ExceptionHandler(this.email_iaas)
notify_customer_decline = Handler(...)

def email_iaas(self, activation):
    # access to previous activation
    prev_activation = activation.prev_activation
    # access to previously caught exception
    exception = prev_activation.caught_exception
    ...

django-viewflow，在处理程序中处理异常的正确方法是什么？

1 个答案: