javascript - 获取错误 : `Every document read in a transaction must also be written` in Firebase

Question

伙计们!

我正在开发一个类似于 https://airtasker.com 的应用程序用户外包任务的地方。任务执行者会对任务出价，并等待用户批准他们的出价。

这些是涉及的集合:

• 任务
• 交易
• 出价

基本上，这个函数应该:

检查是否存在具有给定 taskId 的事务。如果用户开始批准出价，则会添加交易。我允许多个任务者完成任务。

如果交易不存在，它应该添加一个新的，如果达到所需的人力，则将状态标记为正在进行(否则待定)，并更新出价集合以标记已接受的出价。

如果交易存在，它应该检查交易集合中当前批准的列表是否等于人力

如果还没有达到配额人力，推送一个新的tasker并访问出价集合以标记出价已接受。

如果在最后一个条件之后，批准的列表已经达到配额人力，则将任务标记为关闭，并将事务状态更改为正在进行

但我不断收到此错误:

Uncaught (in promise) Error: Every document read in a transaction must also be written. at Transaction.commit (transaction.js:128) at eval (sync_engine.js:244)

这是我的代码:

const acceptOffer = async (taskerId, taskId, bidId, offer) => {
  let bulk
  try {
    const taskRef = db.collection('tasks').doc(taskId)
    const transRef = db.collection('transactions').doc(taskId)
    const bidRef = db.collection('bids').doc(bidId)
    const fees = solveFees(offer)

    bulk = await db
      .runTransaction(async t => {
        const transdoc = await t.get(transRef)
        const taskdoc = await t.get(taskRef)
        const manpower = await taskdoc.get('manpower')

        let status = 'pending'
        if (manpower === 1) {
          status = 'ongoing'
        }

        if (!transdoc.exists) {
          t.set(transRef, {
            taskId,
            status, // pending, ongoing, completed
            approved: [
              { taskerId, ...fees }
            ]
          })

          t.update(bidRef, {
            accepted: true
          })
        } else {
          const approved = await transdoc.get('approved')
          if (manpower < approved.length) {
            approved.push({ taskerId, ...fees })
            t.update(transRef, { approved })
            t.update(bidRef, { accepted: true })

            if (manpower === approved.length) {
              t.update(taskRef, { open: false })
              t.update(transRef, { status: 'ongoing' })
            }
          }
        }
      })
  } catch (e) {
    bulk = e
    console.log('nag error', e)
    throw e
  }

  if (bulk.success) {
    swal('Offer accepted!', '', 'success')
  } else {
    swal('Oh, no!',
      'This task might already be approved',
      'error'
    )
  }
}

我一直卡在这里，因为我不明白交易失败的地方。很感谢任何形式的帮助。

谢谢!

Answer 1

对于那些遇到同样问题的人，这是我的(hackish)解决方案:

对于每个条件，

添加一个文档写入(可以是 set() update() 或 delete())对应于我代码中读取的每个文档: get() 的使用。

并返回一个 Promise

这是更新后的代码:

// a transaction is added if the user starts to approve offers
// this function allows multiple taskers
const acceptOffer = async (taskerId, taskId, bidId, offer) => {
  let bulk
  try {
    const taskRef = db.collection('tasks').doc(taskId)
    const transRef = db.collection('transactions').doc(taskId)
    const bidRef = db.collection('bids').doc(bidId)

    const fees = solveFees(offer)

    bulk = await db
      .runTransaction(async t => {
        const transdoc = await t.get(transRef)
        const taskdoc = await t.get(taskRef)
        const manpower = await taskdoc.get('manpower')

        // check if a transaction exists with the given taskId
        // if it doesn't, then the task doesn't have
        // any approved bidders yet
        if (!transdoc.exists) {
          // check if there is only one manpower required for the task
          // mark the status of the transaction 'ongoing' if so
          const status = manpower === 1
            ? 'ongoing' : 'pending'

          // add a transaction with the approved tasker
          t.set(transRef, {
            taskId,
            status, // pending, ongoing, completed
            approved: [
              { taskerId, ...fees }
            ]
          })

          // mark the bid 'accepted'
          t.update(bidRef, {
            accepted: true
          })

          // hackish (to prevent firestore transaction errors)
          t.update(taskRef, {})

          return Promise.resolve(true)
        } else { // if a transaction exists with the given taskId
          const approved = await transdoc.get('approved')

          // check if the current approved list from
          // the transactions collection hasn't
          // reached the manpower quota yet
          if (approved.length < manpower) {
            // push new approved bid of the tasker
            approved.push({ taskerId, ...fees })
            t.update(transRef, { approved })

            t.update(bidRef, { accepted: true }) // mark the bid 'accepted'
            t.update(taskRef, {}) // hackish

            // if, after pushing a new transaction,
            // the approved list reached the manpower quota
            if (approved.length === manpower) {
              t.update(taskRef, { open: false }) // mark the task 'close'
              t.update(transRef, { status: 'ongoing' }) // mark the transaction 'ongoing'
              t.update(bidRef, {}) // hackish
            }
            return Promise.resolve(true)
          }
          return Promise.reject(new Error('Task closed!'))
        }
      })
  } catch (e) {
    swal('Oh, no!',
      'This task might already be closed',
      'error'
    )
    throw e
  }

  if (bulk) {
    swal('Offer accepted!', '', 'success')
  }
}