使用实时更新时如何检查云 Firestore 文档是否存在

Question

This works:

db.collection('users').doc('id').get()
  .then((docSnapshot) => {
    if (docSnapshot.exists) {
      db.collection('users').doc('id')
        .onSnapshot((doc) => {
          // do stuff with the data
        });
    }
  });

... but it seems verbose. I tried doc.exists , but that didn't work. I just want to check if the document exists, before subscribing to realtime updates on it. That initial get seems like a wasted call to the db.

Is there a better way?

Answer 1

Your initial approach is right, but it may be less verbose to assign the document reference to a variable like so:

const usersRef = db.collection('users').doc('id')

usersRef.get()
  .then((docSnapshot) => {
    if (docSnapshot.exists) {
      usersRef.onSnapshot((doc) => {
        // do stuff with the data
      });
    } else {
      usersRef.set({...}) // create the document
    }
});

Reference: Get a document

Answer 2

In case you are using PHP-Firestore integration, like me, write something like this:

$firestore = new FirestoreClient();
$document = $firestore->document('users/john');
$snapshot = $document->snapshot();

if ($snapshot->exists()) {
   echo "John is there!";
}

Enjoy! o/

Answer 3

Please check following code. It may help you.

 const userDocRef = await firestore().collection('collection_name').doc('doc_id');
   const doc = await userDocRef.get();
   if (!doc.exists) {
     console.log('No such document exista!');
   } else {
     console.log('Document data:', doc.data());
   }

Answer 4

I know its late, but it's actually snapshot.empty not snapshot.exists . snapshot.empty checks if a doc exists and returns accordingly. happy coding 😊

Answer 5

请注意，在火力地堡V9（模块化SDK） exists是一种方法，而不是一个属性（它会给你falsy结果所有的时间），按照该文档。

Answer 6

If you are using Angular you can use the AngularFire package to check it with an observable.

import { AngularFirestore, AngularFirestoreDocument } from '@angular/fire/firestore';

constructor(private db: AngularFirestore) {
  const ref: AngularFirestoreDocument<any> = db.doc(`users/id`);
  ref.get().subscribe(snap => {
    if (snap.exists) {
      // ...
    }
  });
}