Update a field in the last document in Firestore collection Flutter

Question

I am trying to update a field in the last document in the Firestore collection. My updating method is below:

updateHours() {
    return usersRef.doc(firebaseAuth.currentUser!.uid).collection('posts')
        .orderBy('datePublished', descending: true)
        .limit(1).get().then((querySnapshot) {
          return querySnapshot.docs.map((e) {
        usersRef
            .doc(firebaseAuth.currentUser!.uid).collection('posts')
            .doc(e.reference.id)
            .update({"totalTime": FieldValue.increment(1)});
       });
     });
    }

This does not work. If I use .forEach(), then all documents get updated. So, how to update only the last document field?

Answer 1

To be able to update the totalTime field inside the last document, please use the following lines of code:

void updateHours() async{
    CollectionReference postsRef = usersRef
               .doc(firebaseAuth.currentUser!.uid)
               .collection('posts');
    QuerySnapshot query = await postsRef.orderBy('datePublished', descending: true)
               .limit(1)
               .getDocuments();

    query.documents.forEach((doc) {
        doc.reference.updateData({"totalTime": FieldValue.increment(1)});
    });
}

Don't forget that Firebase APIs are asynchronous, and you need to wait for the data until it becomes available.