I get the Alex Mamo's Solution in order to check whether a unique value exists in my database but the snapshot gets always null. The solution is here:
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference userNameRef = rootRef.child("Users").child("Nick123");
ValueEventListener eventListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if(!dataSnapshot.exists()) {
//create new user
}
}
#Override
public void onCancelled(DatabaseError databaseError) {}
};
userNameRef.addListenerForSingleValueEvent(eventListener);
And my database looks like this:
users
(auto-generated push token ID)
fullname
username
gender
...
I don't know whether it's the right method but I used push() method for adding the user object to the database and this method generates push token ID like above.
So, in order not to create duplicate users, what should I change with the above solution? Is there a better method to do this? Maybe like checking the firebase uid with some firebase auth methods?
UPDATE
My database screenshot:
As you see the string just below 'users' is not the same as user's uid.
This is not the best practice when it comes to save user details into the database. First, you should implement Firebase Authentication and then in order to check if a user exist in your database, you should use the following lines of code:
String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference uidRef = rootRef.child("users").child(uid);
ValueEventListener eventListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if(!dataSnapshot.exists()) {
//create new user
}
}
#Override
public void onCancelled(DatabaseError error) {
Log.d("TAG",error.getMessage()); //Don't ignore potential errors!
}
};
uidRef.addListenerForSingleValueEvent(eventListener);
So the key for solving this problem is to call the child() method and pass the UID as an argument instead of calling the push() method that generates an random unique identifier.
If you have this database:
users
(auto-generated push token ID)
fullname
username
gender
Then to check if user exists you need to do the following:
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference userNameRef = rootRef.child("users");
Query queries=userNameRef.orderByChild("fullname").equalTo("Nick123");
ValueEventListener eventListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if(!dataSnapshot.exists()) {
//create new user
}
}
#Override
public void onCancelled(DatabaseError databaseError) {}
};
queries.addListenerForSingleValueEvent(eventListener);
First if you have users lowercase letter, then inside child add users, then you need to use a query to be able to check if the fullname is equal to Nick123.
Usually the database is structured like this:
users
userId
fullname: Nick123
The attributes are key:value, the key is the identifier and Nick123 is the value, so inside the child() method you need to write the identifier which is fullname and not Nick123.
Then since you are able to get the userId, you can do this:
FirebaseUser currentFirebaseUser =FirebaseAuth.getInstance().getCurrentUser();
String userId=currentFirebaseUser.getUid();
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference userNameRef = rootRef.child("users").child(uid).child("fullname");
userNameRef.addValueEventListener(new ValueEventListener(){...}
Related
Can anyone please help? I'm stuck, can't retrieve simple data. This is my code:
And this is my database:
Assuming that the seller note, is a direct child of your database root, to get the value of your userType property, please use the following lines of code:
String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference userTypeRef = rootRef.child("seller").child(uid).child("BasicInfo").child("userType");
ValueEventListener valueEventListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
String userType = dataSnapshot.getValue(String.class);
Log.d("TAG", userType);
if(userType.equals("buyer")) {
//Your logic
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
Log.d("TAG", databaseError.getMessage()); //Don't ignore errors!
}
};
userTypeRef.addListenerForSingleValueEvent(valueEventListener);
Please note that logic regarding the value you get from the database is placed inside the callback because Firebase API's are asynchronous. For more information, please also see my answer from the following post:
How to return DataSnapshot value as a result of a method?
This is the Firebase database structure of my project.
I want to fetch complaint division, describe, stat for the particular hostelname and roomno. How to fetch these data and display in android project?
To get all those values, please use the following lines of code:
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference complaintsRef = rootRef.child("Complaints");
ValueEventListener valueEventListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot ds : dataSnapshot.getChildren()) {
String complaintDivision = ds.child("complaintdivision").getValue(String.class);
//Get the other properties in the same way
Log.d(TAG, complaintDivision);
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
Log.d(TAG, databaseError.getMessage()); //Don't ignore errors!
}
};
complaintsRef.addListenerForSingleValueEvent(valueEventListener);
The output in your logcat will be:
Plumber Related
This is a basic function in Firebase on Android. You can use ValueEventListeners with the database reference to do this.
The steps to achieve the desired results can be enlisted as below:
Create a Complaint model with the same fields as your database.
Get the right Firebase reference for your database node and add a ValueEventListener instance to listen for database changes.
Pass a DataSnapshot into the Complaint class and assign it to a Complaint object.
Do what you want with the Complaint object you have obtained.
Creating a Complaint class:
class Complaint {
// your fields should have the same name as database fields to prevent unnecessary complications
public String complaintdivision;
public String complaintid;
public String describe;
public String hostelname;
public String roomno;
public String stat;
public Complaint(){// required for Firebase
}
}
Getting the data from Firebase:
ArrayList<Complaint> myComplaintArrayList = new ArrayList<>();
FirebaseDatabase.getInstance().getReference().child("Complaints").addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
for(DataSnapshot complaint: dataSnapshot.getChildren()){
Complaint c = complaint.getValue(Complaint.class);
myComplaintArrayList.add(c);// you should have an ArrayList<Complaint> for this loop
}
// do what you want with the items you obtained
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
throw databaseError.toException();
}
});
This is pretty much all of it. If you are still having problems, you should read a tutorial on Firebase.
So to fetch the data you would first declare a Firebase DatabaseReference object that points to your database:
private DatabaseReference mDatabase = FirebaseDatabase.getInstance().getReference();
You would then write a query using this object:
Query query = mDatabase.child("Complaints");
Now you attach a SingleValueEventListener to this query:
query.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
//Write a for-each loop to cycle through your node's children
for(DataSnapshot data: dataSnapshot.getChildren()){
//Create an instance of your model class to
//store the received data
//Make sure you have an empty constructor in your model class
Complaint complaint = data.getValue(Complaint.class);
//then simply call your getters on the complaint object
//to get what you need
complaint.getComplaintDivision();
complaint.getDescription();
//...
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
To fetch more specifically, you just modify the query.
For more information on queries, see this
Let's say I have a Firebase Realtime database structure where there are user nodes and each user node has post nodes that only contain post ids. Then there are also separate post nodes where the actual posts reside (flat data structuring). The structure is described in detail in this answer.
Now if I can get the ids of the posts of each user by attaching a listener to that user's posts node, how can I retrieve the posts themselves (full information from a post node)? I know there aren't any queries where one can pass a bunch of keys and get the associated records. Should I just attach a listener to each post node I am interested in? I'm currently afraid there might be some serious performance issues, because the number of posts is practically unlimited.
Using the exact database structure from this post, to solve your problem, you need to query your database twice. Once to get the post ids of the particular user you need and second to get the posts it self. To achieve this, please use the following code:
String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference postsRef = rootRef.child("users").child(uid).child("posts");
ValueEventListener valueEventListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot ds : dataSnapshot.getChildren()) {
String postId = ds.getKey();
DatabaseReference postIdRef = rootRef.child("posts").child(postId);
ValueEventListener eventListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot dSnapshot : dataSnapshot.getChildren()) {
String postName = dSnapshot.child("postName").getValue(String.class);
Log.d("TAG", postName);
}
}
#Override
public void onCancelled(DatabaseError databaseError) {}
};
postIdRef.addListenerForSingleValueEvent(eventListener);
}
}
#Override
public void onCancelled(DatabaseError databaseError) {}
};
postsRef.addListenerForSingleValueEvent(valueEventListener);
I know this has been asked 100 times already but none of the solutions seem to be working for me.
Want to read the database of "user_preferences" for the user that is signed in (userID) and read the gender/age/weight/height values and store them in the variables shown below. currently returns null on everything (the log statement and the values). Feel like i havent got the path set up properly or something. help would be great!
and my code
mAuth = FirebaseAuth.getInstance();
mFirebaseDatabase = FirebaseDatabase.getInstance();
myRef = mFirebaseDatabase.getReference();
userID = mAuth.getCurrentUser().getUid();
DatabaseReference testRef = myRef.child("user_preferences");
testRef.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot ds : dataSnapshot.getChildren()) { //loop through the firebase nodes
UserPreferences userPreferences = new UserPreferences();
userPreferences.setAge(ds.child(userID).getValue(UserPreferences.class).getAge());
userPreferences.setHeight(ds.child(userID).getValue(UserPreferences.class).getHeight());
userPreferences.setWeight(ds.child(userID).getValue(UserPreferences.class).getWeight());
userPreferences.setGender(ds.child(userID).getValue(UserPreferences.class).getGender());
genderSet = userPreferences.getGender();
age = userPreferences.getAge();
height = userPreferences.getHeight();
weight = userPreferences.getWeight();
Log.d(TAG, "onDataChange: " + genderSet);
//
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
These two lines of code:
DatabaseReference testRef = myRef.child("user_preferences");
testRef.addValueEventListener(...)
are effectively querying the entire node called user_preferences. That means everything at that location - all users. It sounds like this is not what you want. If you want to query just a single user, you should be specific about that in your query by adding the userID that you want to the query location:
DatabaseReference testRef = myRef.child("user_preferences").child(userID);
testRef.addValueEventListener(...)
Also, these lines of code are confusing to me:
userPreferences.setAge(ds.child(userID).getValue(UserPreferences.class).getAge());
userPreferences.setHeight(ds.child(userID).getValue(UserPreferences.class).getHeight());
userPreferences.setWeight(ds.child(userID).getValue(UserPreferences.class).getWeight());
userPreferences.setGender(ds.child(userID).getValue(UserPreferences.class).getGender());
You're deserializing a UserPreferences object for each and every field you want to populate, which is wasteful. It seems to me that you really just want to deserialize it once and remember the object:
UserPreferences userPreferences = dataSnapshot.getValue(UserPreferences.class);
Regarding the null values, you seem to be using external fields, which will not be set until the Firebase returns the network call after at least a second. Your values will be null in the meantime, so you should not be setting them onto a UI element outside of onDataChange.
Also, you have a lot of gets/sets going on, when you only need to call one getValue() for the class, then additional ones for the fields.
Then, you don't seem to want to loop over anything, so you should directly access the user node from the top reference.
For example,
mAuth = FirebaseAuth.getInstance();
mFirebaseDatabase = FirebaseDatabase.getInstance();
myRef = mFirebaseDatabase.getReference();
userID = mAuth.getCurrentUser().getUid();
DatabaseReference testRef = myRef.child("user_preferences/"+userID);
// or .child("user_preferences").child(userID)
testRef.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
UserPreferences userPreferences = dataSnapshot.getValue(UserPreferences.class);
Log.d(TAG, "onDataChange: " + userPreferences.getGender());
// TODO: Update some UI element here
}
#Override
public void onCancelled(DatabaseError databaseError) {
// TODO: Add error handling
}
});
}
If you only want to read the values once, use testRef.addListenerForSingleValueEvent()
I'm working on my app that has a fragment, this fragment displays new users with a follow button using this query :
query = mDatabaseref.child("users").orderByChild("date").limitToLast(10);
After a follow button is clicked, the current User Uid gets saved as a child in the other child that has a name "Follows" with 2 other child's "following" and "followers" as it showed in the below picture :
what I want to do is to make a Query for an other fragment with the name Following and show all the users that the Current user is following with the ability of getting their names, I was thinking of making a data dataSnapshot in the FirebaseRecyclerAdapter onBindViewHolder method basing on the Uid tooken from the childs, but I think it's gonna be complex, on the other hand, i tried to sort the follows in the user Info child direclty, but it leads to a strange behaviour on the RecyclerView.
I'm not going to write you all the code including your FirebaseRecyclerAdapter, I will show you just how to query to get the desired results. As i understand, here is the problem. So in order to achieve this, you need to query your database twice, once to get all those ids and second, based on those ids to get the names. So, please use the following code:
String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference followingRef = rootRef.child("follows").child(uid).child("following");
ValueEventListener valueEventListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot ds : dataSnapshot.getChildren()) {
String userId = ds.getKey();
DatabaseReference userIdRef = rootRef.child("users").child(userId);
ValueEventListener eventListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot dSnapshot : dataSnapshot.getChildren()) {
String name = dSnapshot.child("name").getValue(String.class);
Log.d("TAG", name);
}
}
#Override
public void onCancelled(DatabaseError databaseError) {}
};
userIdRef.addListenerForSingleValueEvent(eventListener);
}
}
#Override
public void onCancelled(DatabaseError databaseError) {}
};
followingRef.addListenerForSingleValueEvent(valueEventListener);
The result in your logcat will be all the names of the followers that belong to a single user.