[英]Android: Retrieve data of a specific user from a Firebase database
I am trying to read "specific" data from my firebase
realtime database. 我正在尝试从firebase
实时数据库中读取“特定”数据。 I have seen examples of getting all data from a table and going through it to find the data record you want, but that is definitly not a recommended safe practice. 我已经看到了一些示例,这些示例从表中获取所有数据并遍历该表以查找所需的数据记录,但这绝对不是推荐的安全做法。
Below is how I save my data 以下是我保存数据的方式
private void saveInDatabase(String email)
{
// Write a message to the database
FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference myRef = database.getReference("user");
String key = myRef.push().getKey();
User user = new User();
user.setCountry("United States");
user.setEmail(email);
user.setFirstName("John");
user.setLastName("Doh");
user.setGender("Male");
myRef.child(key).setValue(user);
}
Well that works great. 很好,效果很好。 But now I need to retrieve the data record from the user
table, that is only belong to John
. 但是现在我需要从user
表中检索数据记录,该数据记录仅属于John
。 If I do this with MySQL, it will be smething like select * from user where primaryKey =JOHN_PRYMARY_KEY
如果我使用MySQL执行此操作,将会像select * from user where primaryKey =JOHN_PRYMARY_KEY
I gave it a try, check below. 我尝试了一下,请在下面检查。
database.getReference("user" + FirebaseAuth.getInstance().getCurrentUser().getUid());
I am really not sure how I can proceed from here, I see no method to go forward. 我真的不确定如何从这里继续前进,我看不到前进的方法。 Please advice. 请指教。
UPDATE UPDATE
I tried the answers from peter haddad and others. 我尝试了彼得·哈达德和其他人的答案。 When I try to get the data from DataSnapshot, it throws a NullPointerException. 当我尝试从DataSnapshot获取数据时,它将引发NullPointerException。 The OnDataChanged is getting fired. OnDataChanged被解雇了。 Below is my database. 下面是我的数据库。
I tried to get data in 3 different ways, check below. 我尝试以3种不同的方式获取数据,请检查以下内容。
----No 1---- ----没有1 ----
private void getUserData()
{
DatabaseReference reference = FirebaseDatabase.getInstance().getReference("user");
reference.orderByChild("email").equalTo(FirebaseAuth.getInstance().getCurrentUser().getEmail()).addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot datas: dataSnapshot.getChildren()){
String familyname=datas.child("familyName").getValue().toString();
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
----No 2---- ----没有2 ----
private void getUserData()
{
FirebaseUser user=FirebaseAuth.getInstance().getCurrentUser();
String userid=user.getUid();
DatabaseReference reference = FirebaseDatabase.getInstance().getReference("user");
reference.child(userid).addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
String email = dataSnapshot.getValue(User.class).getEmail();
String firstName = dataSnapshot.getValue(User.class).getFirstName();
Log.d("Datasnapshot",email+" "+firstName);
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
----No 3---- ----没有3 ----
private void getUserData() {
FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference myRef = database.getReference("user");
Query specific_user = myRef.child(FirebaseAuth.getInstance().getCurrentUser().getUid());
specific_user.addListenerForSingleValueEvent(
new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
//here you will get the data
String email = dataSnapshot.getValue(User.class).getEmail();
String firstName = dataSnapshot.getValue(User.class).getFirstName();
Log.d("Datasnapshot", email + " " + firstName);
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
This is the error I get. 这是我得到的错误。 Based on the codeset I use, the place where the Null pointer trigger get different, the normal behavior. 根据我使用的代码集,空指针触发的位置会有所不同,这是正常行为。
rebaseauth D/NetworkSecurityConfig: No Network Security Config specified, using platform default
04-25 11:49:46.340 31202-31271/com.example.yohan.firebaseauth V/FA: Inactivity, disconnecting from the service
04-25 11:49:47.793 31202-32166/com.example.yohan.firebaseauth W/PersistentConnection: pc_0 - Using an unspecified index. Consider adding '".indexOn": "email"' at user to your security and Firebase Database rules for better performance
04-25 11:49:47.794 31202-31202/com.example.yohan.firebaseauth D/AndroidRuntime: Shutting down VM
04-25 11:49:47.794 31202-31202/com.example.yohan.firebaseauth E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.yohan.firebaseauth, PID: 31202
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference
at com.example.yohan.firebaseauth.MainActivity$6.onDataChange(MainActivity.java:249)
at com.google.firebase.database.Query$1.onDataChange(Unknown Source)
at com.google.android.gms.internal.zzbmz.zza(Unknown Source)
at com.google.android.gms.internal.zzbnz.zzYj(Unknown Source)
at com.google.android.gms.internal.zzboc$1.run(Unknown Source)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6682)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1520)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1410)
You need to do the query: 您需要执行查询:
orderByChild("FirstName").equalTo(name);
DatabaseReference reference = FirebaseDatabase.getInstance().getReference("user");
reference.orderByChild("firstName").equalTo(name).addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot datas: dataSnapshot.getChildren()){
String familyname=datas.child("familyName").getValue().toString();
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
Assuming you have this database: 假设您有此数据库:
user
randomid
firstName: John
familyName: familyName_here
Another way is to use the userid to be able to retrieve the data, but as I see in the question you are saving a random id using push()
. 另一种方法是使用用户ID来检索数据,但是正如我在问题中看到的那样,您正在使用push()
保存随机ID。
You need to retrieve the userid: 您需要检索用户标识:
FirebaseUser user=FirebaseAuth.getInstance().getCurrentUser();
String userid=user.getUid();
then add it to the database: 然后将其添加到数据库中:
myRef.child(userid).setValue(user);
then to retrieve data only for John: 然后仅检索John的数据:
FirebaseUser user=FirebaseAuth.getInstance().getCurrentUser();
String userid=user.getUid();
DatabaseReference reference = FirebaseDatabase.getInstance().getReference("user");
reference.child(userid).addListenerForSingleValueEvent(new ValueEventListener() {..}
Query specific_user = myRef.child(FirebaseAuth.getInstance().getCurrentUser().getUid());
specific_user.addListenerForSingleValueEvent(
new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
//here you will get the data
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
You have to collect the response from firebase to somePOJO Class 您必须收集从firebase到somePOJO类的响应
follow link : https://firebase.google.com/docs/database/admin/retrieve-data 跟随链接: https : //firebase.google.com/docs/database/admin/retrieve-data
As you can see in onDataChange() the response is collected in Post.class which is POJO class. 如您在onDataChange()中所见,响应是在POJO类Post.class中收集的。
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