一旦保存对象，就可以在Firebase中获取已保存的密钥 [英] Get saved key in Firebase as soon as object is saved

问题描述

我是Firebase的新手，到目前为止，Firebase已经走到了尽头。像保存对象和检索对象。我想知道如何获得保存的对象的关键。在休眠状态下，只要保存一个对象，就会返回键。我想知道如何在Firebase中实现这一点。以下是我的代码，但到目前为止我得到nullpointerexception。

  ref.child（Advertisements）。push ）.setValue（mobileAdd）; 
 
 ref.addValueEventListener（new ValueEventListener（）{
 @Override 
 public void onDataChange（DataSnapshot dataSnapshot）{
 
 
 StorageReference storageReference = （）; 
 storageReference.putFile（uri）; 
} 
 
 @Override 
 public void onCancelled（FirebaseError firebaseError）{
 
 
}）; PS：我希望该密钥在Firebase中的存储空间中创建一个文件夹，以便我可以将这些图像保存到创建文件夹。
 
解决方案 
 DatabaseReference.push（）是一个纯粹的客户端操作返回一个引用到一个新的位置，统计保证是唯一的。所以你可以先运行它，并从中获取密钥，然后根据该密钥创建一个存储引用：
 $ b $ pre $  DatabaseReference newDatabaseRef = ref.child（ 广告）推送（）; 
 StorageReference newStorageRef = mStorageReference.child（advertisement）。child（newRef.getKey（））。child（uri.getLastPathSegment（））; 
  

然后最后将值设置到数据库并将文件存储到存储中：

  newDatabaseRef.setValue（mobileAdd）; 
 newStorageRef.putFile（uri）; 
  

I'm new to Firebase and I've come so far with Firebase so far. Like saving objects and retrieving object. I want to know how to get the key of the object saved. In hibernate, it returns key whenever it saves an object. I want to know how this can be achieved in Firebase. Following is the my code, but so far I'm getting nullpointerexception.

 ref.child("Advertisements").push().setValue(mobileAdd);

 ref.addValueEventListener(new ValueEventListener() {
 @Override
 public void onDataChange(DataSnapshot dataSnapshot) {


 StorageReference storageReference = mStorageReference.child("advertisement").child(dataSnapshot.getKey()).child(uri.getLastPathSegment());
 storageReference.putFile(uri);
 }

 @Override
 public void onCancelled(FirebaseError firebaseError) {

 }
 });

PS: I want that key to create a folder in storage in Firebase so I can save those images to that created folder.

解决方案

DatabaseReference.push() is a pure client-side operation that returns a reference to a new location that is statistically guaranteed to be unique. So you can first run that and get the key from it, then create a storage reference based on that key:

DatabaseReference newDatabaseRef = ref.child("Advertisements").push();
StorageReference newStorageRef = mStorageReference.child("advertisement").child(newRef.getKey()).child(uri.getLastPathSegment());

And then finally set the value to the database and put the file to storage:

newDatabaseRef.setValue(mobileAdd);
newStorageRef.putFile(uri);

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