firestore cloud functions onCreate/onDelete sometimes immediately triggered twice

Question

I have observed this behavior occasionally with both onCreate and onDelete triggers.

Both the executions happened for the same document created in firestore. There

Answer 1

In my case I try to use eventId and transaction to prevent onCreate sometimes triggered twice

(you may need to save eventId in list and check if it exist if your function actually triggered often)

const functions = require('firebase-functions')
const admin = require('firebase-admin')
const db = admin.firestore()
exports = module.exports = functions.firestore.document('...').onCreate((snap, context) => {

  const prize = 1000
  const eventId = context.eventId
  if (!eventId) {
    return false
  }

  // increment money
  const p1 = () => {
    const ref = db.doc('...')
    return db.runTransaction(t => {
        return t.get(ref).then(doc => {
          let money_total = 0
          if (doc.exists) {
            const eventIdLast = doc.data().event_id_last
            if (eventIdLast === eventId) {
              throw 'duplicated event'
            }
            const m0 = doc.data().money_total
            if(m0 !== undefined) {
              money_total = m0 + prize
            }
          } else {
            money_total = prize
          }
          return t.set(ref, { 
            money_total: money_total,
            event_id_last: eventId
          }, {merge: true})
        })
    })
  }

  // will execute p2 p3 p4 if p1 success
  const p2 = () => {
    ...
  }

  const p3 = () => {
    ...
  }

  const p4 = () => {
    ...
  }

  return p1().then(() => {
    return Promise.all([p2(), p3(), p4()])
  }).catch((error) => {
    console.log(error)
  })
})