从Firebase查询获取密钥 [英] Getting keys from Firebase query

问题描述

我在从查询结果中获取密钥时遇到问题.这是我的Firebase数据库结构:

I am having problem getting keys from queried results. This is my Firebase Database structure:

{
  "Users" : {
    "7idb6ThWR8aqmnEHFao5GRCV1kI3" : {
      "dPicture" : "https://firebasestorage.googleapis.com/v0/b/parkir-ngasal.appspot.com/o/Profile_images%2Fcropped1465266876.jpg?alt=media&token=44f83fdf-935a-4b3c-8138-561dcba2fca7",
      "status" : "hi my name is erik",
      "uid" : "7idb6ThWR8aqmnEHFao5GRCV1kI3",
      "username" : "erik"
    }
  },
  "posts" : {
    "-KfsrGsY8TWb2wiMFtAq" : {
      "dPicture" : "https://firebasestorage.googleapis.com/v0/b/parkir-ngasal.appspot.com/o/Profile_images%2Fcropped1465266876.jpg?alt=media&token=44f83fdf-935a-4b3c-8138-561dcba2fca7",
      "image" : "https://firebasestorage.googleapis.com/v0/b/parkir-ngasal.appspot.com/o/Post_Images%2Fcropped1354055061.jpg?alt=media&token=77fbc9ed-4356-43c1-b7bb-9563300a8b7b",
      "small_title" : "tes",
      "summary" : "tes",
      "title" : "tes",
      "uid" : "7idb6ThWR8aqmnEHFao5GRCV1kI3",
      "username" : "erik"
    }
  }
}

我正在尝试获取KfsrGsY8TWb2wiMFtAq，但是在下面使用此代码

I am trying to get KfsrGsY8TWb2wiMFtAq, but using this code below

Query mThisUsersPosts;

public static final String TAG = "blah" ;

mDatabasePosts = FirebaseDatabase.getInstance().getReference().child("posts");

mThisUsersPosts = mDatabasePosts.orderByChild("uid").equalTo(mCurrentUser);

mThisUsersPosts.addListenerForSingleValueEvent(new ValueEventListener() {
                  @Override
                  public void onDataChange(DataSnapshot dataSnapshot) {
                      final String posts_key = dataSnapshot.getChildren().toString();
                      Log.d(TAG,posts_key);
                  }

                  @Override
                  public void onCancelled(DatabaseError databaseError) {

                  }
              });

我不明白为什么会得到随机回调，而不是得到结果，例如:

I don't understand why instead of getting the result I am getting random callbacks such as:

com.google.firebase.database.DataSnapshot$1@cfbcf64
com.google.firebase.database.DataSnapshot$1@961642a
com.google.firebase.database.DataSnapshot$1@6f0d191

非常感谢！

推荐答案

对Firebase数据库执行查询时，可能会有多个结果.因此，快照包含这些结果的列表.即使只有一个结果，快照也将包含一个结果的列表.因此，您需要遍历返回快照的子级以获取单个结果.

When you execute a query against the Firebase Database, there will potentially be multiple results. So the snapshot contains a list of those results. Even if there is only a single result, the snapshot will contain a list of one result. So you need to iterate over the children of the returned snapshot to get the individual result(s).

mThisUsersPosts.addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for (DataSnapshot child: dataSnapshot.getChildren()) {
            System.out.println(child.getKey());
            System.out.println(child.child("title").getValue());
        }
    }

请注意，我想知道您选择的数据结构是否适合您的应用程序.如果您的主要用例是显示特定用户的帖子，请考虑对数据进行如下建模:

Note that I wonder if the data structure you picked is right for your app though. If your main use-case is to display the posts for a specific user, consider modeling the data as such:

{
  "Users" : {
    "7idb6ThWR8aqmnEHFao5GRCV1kI3" : {
      "dPicture" : "https://firebasestorage.googleapis.com/v0/b/parkir-ngasal.appspot.com/o/Profile_images%2Fcropped1465266876.jpg?alt=media&token=44f83fdf-935a-4b3c-8138-561dcba2fca7",
      "status" : "hi my name is erik",
      "uid" : "7idb6ThWR8aqmnEHFao5GRCV1kI3",
      "username" : "erik"
    }
  },
  "posts" : {
    "7idb6ThWR8aqmnEHFao5GRCV1kI3": {
      "-KfsrGsY8TWb2wiMFtAq" : {
        "dPicture" : "https://firebasestorage.googleapis.com/v0/b/parkir-ngasal.appspot.com/o/Profile_images%2Fcropped1465266876.jpg?alt=media&token=44f83fdf-935a-4b3c-8138-561dcba2fca7",
        "image" : "https://firebasestorage.googleapis.com/v0/b/parkir-ngasal.appspot.com/o/Post_Images%2Fcropped1354055061.jpg?alt=media&token=77fbc9ed-4356-43c1-b7bb-9563300a8b7b",
        "small_title" : "tes",
        "summary" : "tes",
        "title" : "tes",
        "username" : "erik"
      }
    }
  }
}

通过这种结构，您可以使用更简单/更快的结构为用户获取帖子:

With this structure you can get the posts for the user with the much simpler/faster construct:

mThisUsersPosts = mDatabasePosts.child(mCurrentUser);

mThisUsersPosts.addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for (DataSnapshot child: dataSnapshot.getChildren()) {
            System.out.println(child.getKey());
            System.out.println(child.child("title").getValue());
        }
    }

这篇关于从Firebase查询获取密钥的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！