java - Firebase 数据库使用 map 获取子项的特定值

Question

问题:我正在创建一个允许用户预订服务台的 Android 应用程序，但遇到了如何从 Firebase 实时数据库子值中检索数据的问题。

我的代码目标:我想获取所有用户下所有条目的 userId 和办公 table 号，这样我就可以将已预订的办公 table 设置为在我的 RecyclerView 上显示特定图像用于我的办公 table 选择页面。

我当前的代码:我的 Firebase 数据库为预订设置如下:

{
  "bookings" : {
    "LppMaD3QPBWgMucW8k7mno7tPNu1" : {
      "-L9b5LpjYz8yDwXkPUoh" : {
        "booked" : true,
        "date" : "2018/4/19",
        "desk" : "18",
        "userId" : "LppMaD3QPBWgMucW8k7mno7tPNu1"
      },
      "-L9b5iJGeQ_58geFUkZa" : {
        "booked" : true,
        "date" : "2018/4/13",
        "desk" : "14",
        "userId" : "LppMaD3QPBWgMucW8k7mno7tPNu1"
      },
      "-L9b7tcd8kJJQ-q_7UZo" : {
        "booked" : true,
        "date" : "2018/4/10",
        "desk" : "6",
        "userId" : "LppMaD3QPBWgMucW8k7mno7tPNu1"
      },
      "-L9bCktGaluOj7Rw-7_6" : {
        "booked" : true,
        "date" : "2018/4/20",
        "desk" : "6",
        "userId" : "LppMaD3QPBWgMucW8k7mno7tPNu1"
      }
    }
  }

对于 child :userID，唯一的推送 ID，然后是预订详情。我正在尝试检索唯一推送 ID 下每个条目的办公 table 号码和用户 ID，但我不知道如何获取这些值。

我有一个对预订节点的数据库引用。我有一个用于数据库引用的单值事件监听器。在 onDataChange 方法中，我添加了一个传入 map 和数据快照值的方法。

我可以看到只有一个key(userId和values都是userId的children。

我试图创建一个 map 并从数据快照中获取桌面值，但我的数组大小仅为 1，因为它似乎只是检查键而不是值。我尝试更改对 child("bookings").child(") 的数据库引用以尝试引用 userId，但它返回相同的内容。

我还尝试获取 datasnapshot.child("").getValue(); 的值；但它返回的与 datasnapshot.getValue(); 相同。检查 datasnapshot.getChildren();仅显示 1。

 //Connection to the database, gets a reference to the root of the Firebase JSON tree
    private DatabaseReference mFirebaseDatabaseReference = FirebaseDatabase.getInstance().getReference();

    //Access to the child location
    DatabaseReference mDB = mFirebaseDatabaseReference.child("bookings");

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_select_desk);

        mDB.addListenerForSingleValueEvent(new ValueEventListener()
        {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot)
            {
                if (dataSnapshot.getValue() != null)
                {
                    getDeskAndUser((Map<String,Object>) dataSnapshot.getValue());

                    Log.e(TAG, "Datasnapshot get value: "+dataSnapshot.getValue());
                }
                else
                {
                    Log.e(TAG, "Datasnapshot is null");
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError)
            {

            }
            }
        });
private void getDeskAndUser(Map<String,Object> bookings)
    {

        ArrayList<String> deskNumbers = new ArrayList<>();

        //iterate through each booking, ignoring their UID
        for (Map.Entry<String, Object> desk : bookings.entrySet())
        {
            System.out.println("key=" + desk.getKey() + ", value=" + desk.getValue());

            //Get user map
            Map singleUserDesk = (Map) desk.getValue();
            System.out.println(singleUserDesk);
            //Get desk field and append to list
            deskNumbers.add((String) singleUserDesk.get("desk"));

        }
        ArrayList<String> users = new ArrayList<>();

        for (Map.Entry<String, Object> userId : bookings.entrySet())
        {
            System.out.println("key=" + userId.getKey() + ", value=" + userId.getValue());

            //Get user map
            Map singleUserDesk = (Map) userId.getValue();
            //Get desk field and append to list
            users.add((String) singleUserDesk.get("userId"));

        }

        Log.e(TAG, "Array size is " + bookings.size());
        // Create an ArrayList of BookingDetails objects
        ArrayList<BookingDetails> details = new ArrayList<>();
        for (int i = 0; i < bookings.size(); i++)
        {
            details.add(new BookingDetails());
            Log.e(TAG, "Contents of the array list" + details.toString());

        }
    }

我的 BookingDetails 对象在数据库中创建预订

public class BookingDetails {
  private static final String TAG = "BookingDetails";
  private String userId;
  private String key;
  private String desk;
  private String date;
  private boolean booked;

  public BookingDetails() {}

  public BookingDetails(String userId, String key, String desk, String date, boolean booked) {
    this.userId = userId;
    this.key = key;
    this.desk = desk;
    this.date = date;
    this.booked = booked;

  }

  public String getUserId() {
    return userId;
  }

  public void setUserId(String userId) {
    this.userId = userId;
  }

  public String getKey() {
    return key;
  }

  public void setKey(String key) {
    this.key = key;
  }

  public String getDesk() {
    return desk;
  }

  public String getDate() {
    return date;
  }

  public void setDesk(String desk) {
    this.desk = desk;
  }

  public void setDate(String date) {
    this.date = date;
  }
  public boolean isBooked() {
    return booked;
  }

  public void setBooked(boolean booked) {
    this.booked = booked;
  }
}

还有我的confirmBooking方法来设置数据库中的数据

public void confirm(View view) {
  FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
  if (user != null) {
    // User is signed in
    String userId = user.getUid();
    writeNewBooking(userId, null, mDeskNum, mDateSelected, true);

    Intent confirm = new Intent(this, MyBookingsActivity.class);
    startActivity(confirm);

  } else {
    // No user is signed in
    Log.e(TAG, "No user is signed in!");
  }
}

private void writeNewBooking(String userId, String key, String desk, String date, Boolean booked) {
  DatabaseReference postsRef = mFirebaseDatabaseReference.child("bookings").child(userId);
  DatabaseReference newPostRef = postsRef.push();
  newPostRef.setValue(new BookingDetails(userId, key, desk, date, booked));
  newPostRef.getKey();
}

Answer 1

要解决这个问题，请使用以下代码:

String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference uidRef = rootRef.child("bookings").child(uid);
ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            String desk = ds.child("desk").getValue(String.class);
            String userId = ds.child("userId").getValue(String.class);
            Log.d("TAG", desk + " / " + userId);
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {}
};
uidRef.addListenerForSingleValueEvent(valueEventListener);

其中对应登录用户的uid为LppMaD3QPBWgMucW8k7mno7tPNu1。

输出将是:

18 / LppMaD3QPBWgMucW8k7mno7tPNu1
14 / LppMaD3QPBWgMucW8k7mno7tPNu1
6 / LppMaD3QPBWgMucW8k7mno7tPNu1
6 / LppMaD3QPBWgMucW8k7mno7tPNu1