修复云函数数组循环-写入长延迟

Question

我有一个云函数，它遍历一个uids数组，然后为每个uids创建一个写。正常的写几乎是瞬间发生的，但是在写出来之前还有很长的时间。

我试过不同尺寸的阵列。只有一两个uids的数组速度更快，但仍有5-6秒的滞后。

exports.addPostings = functions.firestore
    .document('posts/{postID}')
    .onCreate((snap, context) => {
    const newValue = snap.data();
    var uid = newValue.author.uid;
    let followers = [];
    var feedRef = db.collection("feedItems");
    var authorRef = db.collection("users").doc(newValue.author.uid);
    authorRef.get().then((doc) => {
        let data = doc.data();
        let post_count = data.postCount;
        authorRef.update({
            postCount: Number(post_count) + 1
        }).then(() => {
            authorRef.collection('followers').doc('content').get().then((doc) => {
                let data = doc.data();
                if (typeof data.uids != 'undefined') {
                    followers = data.uids;
                }
            }).then(() => {
                followers.forEach((fol) => {
                  feedRef.add({
                      createdAt: admin.firestore.FieldValue.serverTimestamp(), uid: fol, creatorUid: uid,
                      postId: context.params.postID, isResharedPost: false, wasViewed: false,
                      wasReshared: false, wasLiked: false, wasDirectlyShared: false
                  });
                });
            });
        });
    });
});

Answer 1

您应该在代码中修改以下几点：

1. 您不会返回异步方法()返回的承诺，这是编写云函数代码时的关键，正如官方Firebase视频系列：https://firebase.google.com/docs/functions/video-series/中关于"JavaScript承诺“的3段视频所解释的那样
2. 你应该正确地连锁承诺。
3. 您应该使用批次写入，如CuriousGeorge所示

下面的修改应该能做到这一点(但是没有测试！)：

exports.addPostings = functions.firestore
  .document('posts/{postID}')
  .onCreate((snap, context) => {
    const newValue = snap.data();
    var uid = newValue.author.uid;
    let followers = [];
    var feedRef = db.collection('feedItems');
    var authorRef = db.collection('users').doc(newValue.author.uid);

    return authorRef
      .get()
      .then(doc => {
        let data = doc.data();
        let post_count = data.postCount;
        return authorRef.update({
          postCount: Number(post_count) + 1
        });
      })
      .then(() => {
        return authorRef
          .collection('followers')
          .doc('content')
          .get();
      })
      .then(doc => {
        let data = doc.data();
        if (typeof data.uids != 'undefined') {
          followers = data.uids;

          let batch = db.batch();

          followers.forEach(fol => {
            const ref = feedRef.doc();
            batch.set(ref, {
              createdAt: admin.firestore.FieldValue.serverTimestamp(),
              uid: fol,
              creatorUid: uid,
              postId: context.params.postID,
              isResharedPost: false,
              wasViewed: false,
              wasReshared: false,
              wasLiked: false,
              wasDirectlyShared: false
            });
          });

          // Commit the batch
          return batch.commit();
        } else {
          return null;
        }
      });
  });

Answer 2

此外，您应该在这里研究如何使用transactions.batched编写。这允许您定义一系列的读/写，然后同时执行它们。此方法可能比较慢的部分原因是您正在执行多个读/写(在处理过程中出现故障时，这也是不好的)。https://firebase.google.com/docs/firestore/manage-data/transactions#transactions