java - 如何在云Firestore中使用Firebase正确重写代码？

Question

我写信是为了连接到 Firebase，现在我想将所有内容传输到云端 Firestore1)第一个方法是为了从firebase获取“Comment”而编写的

private void iniRvComment() {
        RvComment.setLayoutManager(new LinearLayoutManager(this));
        DatabaseReference commentRef = firebaseDatabase.getReference(COMMENT_KEY).child(postKey);
        commentRef.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                listComment = new ArrayList<>();
                for(DataSnapshot snapshot: dataSnapshot.getChildren()){
                    Comment comment = snapshot.getValue(Comment.class);
                    listComment.add(comment);
                }
                commentAdapter = new CommentAdapter(getApplicationContext(), listComment);
                RvComment.setAdapter(commentAdapter);
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {

            }
        });
    }

2) 以及如何重写此代码以从云 Firestore 获取“评论”。我下面写的不正确

private void iniRvComment() {
        RwComment.setLayoutManager(new LinearLayoutManager(this));
        DocumentReference docRef = firestore.collection("Comment").document(postKey);
        docRef.collection("Comment").addSnapshotListener(new EventListener<QuerySnapshot>() {
            @Override
            public void onEvent(@Nullable QuerySnapshot documentSnapshot, @Nullable FirebaseFirestoreException e) {
                if (documentSnapshot != null && !documentSnapshot.getDocuments().isEmpty()) {
                    listComment = new ArrayList<>();
                    List<DocumentSnapshot> documents = documentSnapshot.getDocuments();
                    for (DocumentSnapshot value : documents) {

                        Comment comment = value.toObject(Comment.class);
                        listComment.add(comment);
                    }
                    commentAdapter = new CommentAdapter(getApplicationContext(), listComment);
                    RwComment.setAdapter(commentAdapter);
                }
            }
        });
    }

Answer 1

我建议将您的评论扁平化到单个顶级 Comments 集合中，而不是将它们存储在帖子下。这将允许您执行许多有用的搜索操作，例如按用户或帖子搜索所有评论，甚至创建“最近活跃的帖子”提要。

要实现这一点，您需要更改数据库结构，以便所有评论都与它们所附加的帖子一起存储。

{
  content: "...",
  timestamp: 1234534568425,
  postId: "...",
  uid: "...",
  uimg: "...",
  uname: "..."
}

完成此操作后，您现在可以使用以下方式通过帖子查询评论:

private final int PAGE_SIZE = 10;
private void iniRvComment() {
  RvComment.setLayoutManager(new LinearLayoutManager(this));

  firestore.collection("Comments") // this is a top level collection
    .whereEqualTo("postId", postKey) // select comments for given post
    .orderBy("timestamp", Query.Direction.DESCENDING) // order newest to oldest
    .limit(PAGE_SIZE) // fetch up to PAGE_SIZE recent comments
    .addSnapshotListener(new EventListener<QuerySnapshot>() {
      @Override
      public void onEvent(@Nullable QuerySnapshot results,
                          @Nullable FirebaseFirestoreException e) {
        if (e != null) {
          Log.w(TAG, "Listen failed.", e);
          return;
        }

        listComment = new ArrayList<>(PAGE_SIZE);
        for (QueryDocumentSnapshot commentDoc : results) {
          Comment commentObj = commentDoc.toObject(Comment.class);
          listComment.add(commentObj);
        }

        commentAdapter = new CommentAdapter(getApplicationContext(), listComment);
        RvComment.setAdapter(commentAdapter);
        Log.d(TAG, "Retrieved " + results.size() + " recent comments.");
      }
    });
}