Firebase - accessing the most recent entry

I have a node server up and running where I need to monitor updates in a collection and retrieve the newly added data. My approach was to utilize db.collection("posts").onSnapshot to listen for updates and fetch the latest entry by ordering it based on date.

db.collection("posts").onSnapshot(async () => {
  const newPost = await db
    .collection("posts")
    .orderBy("date", "desc")
    .limit(1)
    .get()
    .data();
  console.log(newPost);
});

However, when using .data(), an error occurs since it's not a recognized function for retrieving the data. After some debugging attempts, I couldn't identify any keys within the object that would grant me access to the post data.

This is the current output without utilizing .data()

    QuerySnapshot$1 {
  _delegate:
   QuerySnapshot {
     _firestore:
      FirebaseFirestore$1 {
        _persistenceKey: '[DEFAULT]',
        _settings: [FirestoreSettings],
        _settingsFrozen: true,
        _app: [FirebaseAppImpl],
        _databaseId: [DatabaseId],
        _credentials: [FirebaseCredentialsProvider],
        _queue: [AsyncQueue],
        _firestoreClient: [FirestoreClient] },
     _userDataWriter: UserDataWriter { firestore: [Firestore] },
     _snapshot:
      ViewSnapshot {
        query: [QueryImpl],
        docs: [DocumentSet],
        oldDocs: [DocumentSet],
        docChanges: [Array],
        mutatedKeys: [SortedSet],
        fromCache: false,
        syncStateChanged: true,
        excludesMetadataChanges: false },
     metadata:
      SnapshotMetadata { hasPendingWrites: false, fromCache: false },
     query:
      Query {
        _converter: null,
        _query: [QueryImpl],
        type: 'query',
        firestore: [FirebaseFirestore$1] } },
  _firestore:
   Firestore {
     _delegate:
      FirebaseFirestore$1 {
        _persistenceKey: '[DEFAULT]',
        _settings: [FirestoreSettings],
        _settingsFrozen: true,
        _app: [FirebaseAppImpl],
        _databaseId: [DatabaseId],
        _credentials: [FirebaseCredentialsProvider],
        _queue: [AsyncQueue],
        _firestoreClient: [FirestoreClient] },
     _persistenceProvider: IndexedDbPersistenceProvider {},
     INTERNAL: { delete: [Function: delete] },
     _appCompat:
      FirebaseAppImpl {
        firebase_: [Object],
        isDeleted_: false,
        name_: '[DEFAULT]',
        automaticDataCollectionEnabled_: false,
        options_: [Object],
        container: [ComponentContainer] } } }

Answer №1

To retrieve data from Firestore, your code needs to await the result of the get() function and then access the returned QuerySnapshot to extract the document information. Keep in mind that a QuerySnapshot can contain zero or multiple documents, so it's important to check if any documents were returned using its API. Even if you expect only one document, you still have to loop through the result set to find that specific document.

const latestPost = await db
    .collection("posts")
    .orderBy("date", "desc")
    .limit(1)
    .get();
  // latestPost is now a QuerySnapshot
  if (latestPost.size > 0) {
    const postDetails = latestPost.docs[0].data();
    // manipulate the document data as needed
  }
  else {
    // handle the scenario where no documents were found
  }

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