为什么我不能在 Redux-Saga 的 for..in 循环中使用嵌套的 yield [英] Why can't I use nested yield in for..in loop in Redux-Saga

问题描述

所以我有带有 ID 和值的 tasks 对象.使用 for in 循环，我想读取成员"属性.如果它存在，并且数组的第一个元素 !=='all' 我想通过给定的 id 向 firebase 发出请求以读取文档.但是我不能使用yield，出现错误:

So I have tasks object with ids and values. With for in loop I want to read 'members' property. If it exist, and first element of array !=='all' I want to make request to firebase for read document by given id. But I cant use yield, there is error:

Failed to compile.

./src/containers/modules/Tasks/store/sagas/tasksSagas.js
  Line 27:  Parsing error: Unexpected reserved word 'yield'

为什么我会得到它?我不能使用嵌套收益?

Why am I getting it? I can't use nested yields?

//Fetching users for tasks
  for (const task in tasks) {
    if (tasks[task].hasOwnProperty('members')) {
      if (tasks[task].members[0]==='all'){
        tasks[task].fetchedMembers = ['all']
      }
      else {
        const fetchedMembers = tasks[task].members.map(member => {
          const user = yield db.collection('users').doc(member).get()
          const userData = user.data()
          return {
            uid: member,
            ...userData
          }
        })
        tasks[task].fetchedMembers = fetchedMembers
      }
    }
  }

推荐答案

const fetchedMembers = tasks[task].members.map(member => {
  const user = yield db.collection('users').doc(member).get()
  const userData = user.data()
  return {
    uid: member,
    ...userData
  }
})

您传递给 .map 的函数不是生成器函数，因此您不能在其中使用 yield.并且它不能是生成器函数，因为 map 对生成器或传奇一无所知.

The function you pass to .map is not a generator function, so you can't use yield in it. And it can't be a generator function, since map knows nothing about generators or sagas.

一个选择是创建一个 promise 数组，然后产生它(或者包裹在 Promise.all 中，或者 redux-saga 的 all effect):

One option is to create an array of promises, and then yield that (either wrapped in Promise.all, or redux-saga's all effect):

const promises = tasks[task].members.map(member => {
  return db.collection('users').doc(member).get();
})

const members = yield all(promises);
const fetchedMembers = members.map(user => {
  const userdata = user.data();
  return {
    uid: member,
    ...userData;
  }
);

另一种选择是为每个成员编写一个你想要做的迷你传奇，然后创建一个调用效果数组，然后产生所有这些:

Another option is to write a mini-saga you want to do for each member, and then create an array of call effects, then yield all of those:

const callEffects = tasks[task].members.map(member => {
  return call(function* () {
    const user = yield db.collection('users').doc(member).get()
    const userData = user.data()
    return {
      uid: member,
      ...userData
    }
  });
})

const fetchedMembers = yield all(callEffects);

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