通过Firebase中的ID检索Java对象 [英] Retrieve Java object by ID from Firebase

问题描述

我正在编写一个Android应用程序，我试图从其Firebase相关表中检索类 User.java 的对象。我想知道如何从Java端获得它，只要我尝试了 Firebase官方文档，但他们都没有为我工作。

以这个问题为例，我想要一个具有以下方法接口：

  public User readUser（String userId）; 
  

换句话说，我想执行：

readUser（-lnnROTBVv6FznK81k3n）

并检索关联的 User object

谢谢

----------- -------------------------------------------------- -编辑 - - - - - - - - - - - - - - - - - - - - - - - - -------------- ：

我设法得到这个代码的值：

  public void retrieveUser（final String email）{
 firebaseUsersRef.addValueEventListener（new ValueEventListener（）{
 @Override 
 （DataSnapshot messageSnapshot：dataSnapshot.getChildren（））{
 if（messageSnapshot.getKey（）。equals（Email.encodeID（email）））{$ b $ public void onDataChange（DataSnapshot dataSnapshot）{
 b 
 retrieveUser = messageSnapshot.getValue（User.class）; 
 break ; 
 
 
 
 @Override 
 public void onCancelled（FirebaseError firebaseError）{} 
}）; 
 
  

请不要retrieveUser是一个类属性，因此字段。我从代码访问该字段，但即使我看到它在调试器上的值，调用代码上为空。

任何提示？我不能只是在方法本身返回它，所以它会是：

  public User retrieveUser（final String email） ; 
  

谢谢

解决方案 div>

所以这里是灵魂，我没有把它放在一个方法，虽然。

 最终字符串uid = 你的UID在这里; 
 //获取对用户的引用
 Firebase ref = new Firebase（Constants.FIREBASE_URL_USERS）; 
 //附加一个监听器来读取我们的用户
 ref.addValueEventListener（new ValueEventListener（）{
 @Override 
 public void onDataChange（DataSnapshot snapshot）{
 
 for（DataSnapshot user：snapshot.getChildren（））{
 //这就是您需要通过Uid 
获取特定用户所需的全部内容if（user.getKey（）。equals（uid））{ 
 wantedUser = user.getValue（User.class）; 
} 
 // ************************ ********************** 
 
} 
 Log.i（TAG，onDataChange：+ wantedUser.getName ））; 
} 
 @Override 
 public void onCancelled（FirebaseError firebaseError）{
 System.out.println（The read failed：+ firebaseError.getMessage（））; 
} 
}）; 
  

I am writing an Android app and I am trying to retrieve an object of the class User.java by ID from its Firebase pertinent table. I would like to know how to get it from Java side, as long as I tried the examples stated in Firebase Official docs but none of them is working for me.

Taking this SO question as example, I want a method with the following interface:

public User readUser(String userId);

In other words, I want to execute:

readUser(-lnnROTBVv6FznK81k3n)

and retrieve the associated User object

Thanks

--------------------------------------------------------------EDIT--------------------------------------------------------------:

I managed to get the value with this code:

public void retrieveUser(final String email){
        firebaseUsersRef.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                for (DataSnapshot messageSnapshot: dataSnapshot.getChildren()) {
                    if(messageSnapshot.getKey().equals(Email.encodeID(email))){

                        retrievedUser = messageSnapshot.getValue(User.class);
                        break;
                    }
                }
            }

            @Override
            public void onCancelled(FirebaseError firebaseError) { }
        });
    }

Please not retrievedUser is a class attribute, thus a field. I am accessing that field from the code, but even I see it takes the value on the debugger, it is being null on the calling code.

Any hint? Can´t I just return it in the method itself, so it would be?:

public User retrieveUser(final String email);

Thanks

解决方案

so here is the soultion, I didn't put it in a method though.

final String uid = "your Uid here"; 
        // Get a reference to users
        Firebase ref = new Firebase(Constants.FIREBASE_URL_USERS);
        // Attach an listener to read our users
        ref.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot snapshot) {

                for (DataSnapshot user: snapshot.getChildren()) {
               //this is all you need to get a specific user by Uid
                    if (user.getKey().equals(uid)){
                        wantedUser = user.getValue(User.class);
                    }
               //**********************************************

                }
                Log.i(TAG, "onDataChange: " + wantedUser.getName());
            }
            @Override
            public void onCancelled(FirebaseError firebaseError) {
                System.out.println("The read failed: " + firebaseError.getMessage());
            }
        });

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