参数未传递给 firebase 云函数中的本地函数

Question

I have a firebase cloud function as follows:

exports.foo = functions.database
  .ref("/candidates/{jobTrack}/{candidateId}")
  .onCreate((snap, context) => {
    const candidate = snap.val().candidate;
    const jobTrack = context.params.jobTrack;

    const jobsRef = admin.database().ref("jobs");
    return jobsRef
      .child(jobTrack)
      .once("value")
      .then(jobs => {
        const promises = [];

        jobs.forEach(job => {
          promises.push(job.val());
        });

        return Promise.all(promises);
      })
      .then(jobs => {
        return jobs.forEach(job => {
          var percent = getMatchedPercent(candidate, job);
          if (percent >= 0.9) {
            admin
              .database()
              .ref("feeds")
              .child(job.feedId)
              .child("upcomingWeek")
              .push(candidate); // add to team's feed
          }
        });
      })
      .catch(err => {
        console.log("firebase got an error: ", err);
      });
  });

In function foo , I call a local non-cloud function getMatchedPercent which is defined as below:

const getMatchedPercent = (candidate, job) => {
  console.log("In get percent: ", candidate, job);
  // do something
};

The problem is when I checked job.val() in foo before calling getMatchedPercent , I can see valid data got printed from console for job.val() . When once get in getMatchedPercent , I tried to print job , it complains it's undefined .

Is there anything I missed? Why the information of job can be lost during calling a function? Thanks!

Answer 1

Your problem is caused by these lines:

const promises = [];

jobs.forEach(job => {
  promises.push(job.val());
});

return Promise.all(promises);

job.val() returns an object (of the data) not a promise, so Promise.all() incorrectly interprets it as a resolved promise with no value. In your next block of code, the array jobs is an array of undefined values rather than the data you were expecting.

To fix this, you would instead return the array of values rather than using Promise.all() .

const jobValues = [];

jobs.forEach(job => {
  jobValues.push(job.val());
});

return jobValues;

But because no asyncronous work is taking place here you can flatten your Promise chain. By doing so, you will use less memory because you won't need an array containing of all of your job.val() objects at once.

exports.foo = functions.database
  .ref("/candidates/{jobTrack}/{candidateId}")
  .onCreate((snap, context) => {
    const candidate = snap.val().candidate;
    const jobTrack = context.params.jobTrack;

    const jobsRef = admin.database().ref("jobs");
    return jobsRef
      .child(jobTrack)
      .once("value")
      .then(jobs => {
        const promises = []; // will contain any team feed update promises

        jobs.forEach(jobSnapshot => { // This is DataSnapshot#forEach
          const job = jobSnapshot.val();
          const percent = getMatchedPercent(candidate, job);
          if (percent >= 0.9) {
            promises.push(
              admin
                .database()
                .ref("feeds")
                .child(job.feedId)
                .child("upcomingWeek")
                .push(candidate) // add to team's feed
            );
          }
        });

        return Promise.all(promises);
      })
      .catch(err => {
        console.log("Failed to update team feeds: ", err);
      });
  });

However, this still has another problem where some of the feed updates may succeed and others may fail which leaves your database in an unknown state. So instead you might want to consider writing to the database atomically (all data is written, or nothing at all).

This could be achieved using:

exports.foo = functions.database
  .ref("/candidates/{jobTrack}/{candidateId}")
  .onCreate((snap, context) => {
    const candidate = snap.val().candidate;
    const jobTrack = context.params.jobTrack;

    const jobsRef = admin.database().ref("jobs");
    return jobsRef
      .child(jobTrack)
      .once("value")
      .then(jobs => {
        const pendingUpdates = {}; // "path: value" pairs to be applied to the database
        const feedsRef = admin.database().ref("feeds");

        jobs.forEach(jobSnapshot => { // This is DataSnapshot#forEach
          const job = jobSnapshot.val();
          const percent = getMatchedPercent(candidate, job);

          if (percent >= 0.9) {
            const pushId = feedsRef.push().key; // push() without arguments doesn't write anything to the database, it just generates a new reference with a push ID we can use.
            const path = job.feedId + "/upcomingWeek/" + pushId;
            pendingUpdates[path] = candidate; // queue add to team's feed
          }
        });

        // apply all updates in pendingUpdates object,
        // relative to feedsRef as an all-or-nothing operation.
        // e.g. pendingUpdates["feed001/upcomingWeek/9jksdfghsdjhn"] = "someUserId"
        //      will be written to "feeds/feed001/upcomingWeek/9jksdfghsdjhn"
        return feedsRef.update(pendingUpdates); // commit changes
      })
      .catch(err => {
        console.log("Failed to apply all feed updates: ", err);
      });
  });