Question

我是firebase的新用户，我试图在Users中获取数据的大小，其中Users具有不同的records，并且每条记录都有两个属性Name和Contact。我希望在cont中获得records的大小。我试图在Android应用程序中使用java。

数据库的结构看起来像这样

Users

   Records
        Name
        Contact

我想得到记录的数量。

Answer 1

假设您的数据库结构如下所示：

Firebase-root
    |
    --- users
          |
          --- uidOne
          |    |
          |    --- name: "NameOne"
          |    |
          |    --- contact: "ContactOne"
          |
          --- uidTwo
               |
               --- name: "NameTwo"
               |
               --- contact: "ContactTwo"

要获得用户数，请使用以下代码：

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference usersRef = rootRef.child("users");
ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        long count = dataSnapshot.getChildrenCount();
        Log.d("TAG", "count= " + count);
    }

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

Answer 2

使用值侦听器

FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference myRef = database.getReference();

//You can use the single or the value.. depending if you want to keep track
thismyRef.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
    for (DataSnapshot snap: dataSnapshot.getChildren()) {
        Log.e(snap.getKey(),snap.getChildrenCount() + "");
    }
}

@Override
public void onCancelled(DatabaseError databaseError) {

}
});

Answer 3

您所需要的只是DataSnapshot。

另请查看此SO question

Answer 4

要获得计数，只有一行dataSnapshot.getChildrenCount();

请参阅下面的答案

ref.addListenerForSingleValueEvent(new ValueEventListener() { //ref will be your desired path where you want to count children
                    @Override
                    public void onDataChange(DataSnapshot dataSnapshot) {
                        if (dataSnapshot.getValue() != null) {   // Check for data snapshot has some value
                            dataSnapshot.getChildrenCount()  // check for counts of data snapshot children
                           }
                    }

                    @Override
                    public void onCancelled(DatabaseError databaseError) {

                    }
                });

如何获取Firebase数据库中的记录大小？

4 个答案: