I am trying to retrieve a list that is on a child that starts with something. Below is a sample of data in my Firebase realtime database:
In the image, I want to retrieve all data that starts with the keyword "jsonmat".
I am using thee code below but it always return null:
DatabaseReference db = FirebaseDatabase.getInstance().getReference()
.child("Events");
db.startAt("jsonmat").addListenerForSingleValueEvent(
new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
Log.i("events", dataSnapshot.toString());
for (DataSnapshot data : dataSnapshot.getChildren()) {
// here the user will have the specified email only
}
}
#Override
public void onCancelled(DatabaseError databaseError){
Log.i("MyApp", "getUser:onCancelled", databaseError.toException());
}
});
What you're trying to do isn't possible. You can't order/filter of a nested key, only on direct child keys (-M...) and on nested values (active: true).
Typically you'll want to create a new top-level node, where you store the keys you're searching for, and then the push keys for each matching nested node:
"category_things": {
"jsonmat_jsonmat": {
"-M62....uYgB": true,
"-M62....2-eO": true
}
}
Also see:
Firebase Query Double Nested
My original, but wrong answer is below...
If you use startAt without specifying an orderBy... clause, the data will be ordered by priority. This priority is a left-over from before Firebase supported ordering on specific properties, so mostly it means that you must call an orderBy... method before filtering.
So:
DatabaseReference db = FirebaseDatabase.getInstance().getReference().child("Events");
db.orderByKey().startAt("jsonmat").addListenerForSingleValueEvent(new ValueEventListener() {
...
What you can do for your case, is to loop 2 times over the children of the node Events:
//the reference to the node Events
DatabaseReference db = FirebaseDatabase.getInstance().getReference().child("Events");
db.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
//loop 1
for (DataSnapshot data : dataSnapshot.getChildren()) {
//loop2
for (DataSnapshot dataTwo : data.getChildren()) {
//get the key
String key = dataTwo.getKey();
if(key.startsWith("jsonmat")){
//we got a matching key so extract the data and maybe put them in a list
boolean active = dataTwo.child("active").getValue(Boolean.class);
int bet = dataTwo.child("bet").getValue(Integer.class);
String challenger = dataTwo.child("challenger").getValue(String.class);
String competitor = dataTwo.child("competitor").getValue(String.class);
String game = dataTwo.child("game").getValue(String.class);
............
............
............
}else{
//we didn't get a match
}
}//end loop2
}//end loop1
}
#Override
public void onCancelled(DatabaseError databaseError){
Log.i("MyApp", "getUser:onCancelled", databaseError.toException());
}
});
Related
I am trying to update a value in my Firebase database. This is the structure of the database:
I need to update the value of status to "accepted" if the r_id and s_id have a specific value. The problem here is that the key for each friend_data child is generated using "push" like this
db.child("friend_data").push().setValue(friend);
I have tried this question here and this one here but both don't meet my requirements. How do I go about solving this one?
Edit: I understand now that I am supposed to use a Query here. This is what I tried:
final DatabaseReference db = FirebaseDatabase.getInstance().getReference("friend_data");
Query query = db.orderByChild("r_id").equalTo(f_id).orderByChild("s_id").equalTo(id);
query.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot child : dataSnapshot.getChildren()) {
db.child(child.getKey()).child("status").setValue("accepted");
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
This does not work either because this error is raised
java.lang.IllegalArgumentException: You can't combine multiple orderBy calls!.
So how do I combine two Queries?
I have finally got this to work after days of trying to figure it out.
I added a Query with orderByChild method to filter out a big chunk of data at the server side itself (thanks to this answer for the idea.) The remaining data which I got as child of data type DataSnapshot had all the necessary information that I needed. Here is the query
Query query = db.orderByChild("r_id").equalTo(f_id);
query.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot child : dataSnapshot.getChildren()) {
String child_s_id = (String) child.child("s_id").getValue();
String child_status = (String) child.child("status").getValue();
if (child_s_id.equals(id)) {
Log.e("Got value", f_id + " - x -" + id + " " + child_status);
}
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
But again I could not meet my requirements, because I actually needed to modify one of the value in the child and I could not use any methods like setValue to change the value of child.
Again, it took me a long while (what an idiot) to figure out that I had to convert the child (of data type DataSnapShot) to a reference for setValue to work. And it worked
child.getRef().child("status").setValue("accepted");
Here is the completed code. Hope it helps someone along the way
Query query = db.orderByChild("r_id").equalTo(f_id);
query.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot child : dataSnapshot.getChildren()) {
String child_s_id = (String) child.child("s_id").getValue();
String child_status = (String) child.child("status").getValue();
if (child_s_id.equals(id))
child.getRef().child("status").setValue("accepted");
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
I am storing user details 'firstname' and 'lastname' in UserNode. But when i want to retrieve that details then no data is being retrieved. I tried almost all solutions on the internet but nothing solved my problem. Here is my code for retrieving data of the current user:
FirebaseUser userr = FirebaseAuth.getInstance().getCurrentUser();
if (userr != null) {
String name = userr.getDisplayName();
Log.e("value", name);
}
but it says "println needs a message"
I also tried with this but nothing happened:
DatabaseReference DataRef;
DataRef = FirebaseDatabase.getInstance().getReference().child("UserNode");
DataRef.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
String acctname = (String)dataSnapshot.child("firstname").getValue();
Log.e("name", acctname);
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
]1
Please help me I am stuck with it
You're reading a collection of user with a ValueEventListener. As the [Firebase documentation for reading lists with a value event](Listen for value events) explains:
While using a ChildEventListener is the recommended way to read lists of data, there are situations where attaching a ValueEventListener to a list reference is useful.
Attaching a ValueEventListener to a list of data will return the entire list of data as a single DataSnapshot, which you can then loop over to access individual children.
Even when there is only a single [child node], the snapshot is still a list; it just contains a single item. To access the item, you need to loop over the result.
So in your code:
DatabaseReference DataRef;
DataRef = FirebaseDatabase.getInstance().getReference().child("UserNode");
DataRef.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot childSnapshot: dataSnapshot.getChildren()) {
String acctname = (String)childSnapshot.child("firstname").getValue();
Log.i("name", acctname);
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
throw databaseError.toException(); // don't ignore errors
}
});
Using FirebaseUser:
FirebaseUser implements UserInfo and in UserInfo's getDisplayName() documentation says
Returns the user's display name, if available.
So, it is possible that FirebaseUser.getDisplayName() return null when display name is not set. In that case Log.e() receives null as message and therefore prints println needs a message
Using your own structure:
Instead of using type conversion use getValue(Class<T>) like so:
String acctname = dataSnapshot.child("firstname").getValue(String.class);
Please, read how to retrieve data from firebase. I think you have a problem because you don't have Class Model.
Your steps:
Create model UserModel with firstname and lastname field
Use listener (example from docs):
// Attach a listener to read the data at our posts reference
ref.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
Post post = dataSnapshot.getValue(Post.class);
System.out.println(post);
}
#Override
public void onCancelled(DatabaseError databaseError) {
System.out.println("The read failed: " + databaseError.getCode());
}
});
See other answers: How to retrieve data from one single userID Firebase Android and retrieving data from firebase android
I've been trying to retrieve an element from my Firebase database using its key. I have a class User and users are present in database.
I want to retrieve an object user using its key with this method :
public User getConnectedUserByUId(final String uid){
DatabaseReference database = FirebaseDatabase.getInstance().getReference();
DatabaseReference ref = database.child("users");
final List<User> connectedUser= new ArrayList<User>();
ref.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot item: dataSnapshot.getChildren()) {
if (item.getKey()==uid)
{
User user= dataSnapshot.getValue(User.class);
connectedUser.add(user);
}
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
return connectedUser.get(0);
}
but it returns an empty list every time.
The issue is here:
if (item.getKey()==uid)
since you are comparing 2 String in java you have to use the method
string.equals(Object other) not the == operator.
Moreover, since you know the key of the data in Firebase you can use it to get the reference without cycling all children.
Something like:
DatabaseReference database = FirebaseDatabase.getInstance().getReference();
DatabaseReference ref = database.child("users").child(uid);
Here you try to check a very specific ID only on changed data. Instead, try using a Firebase Query with filterByKey and not using your own function to achieve that. Here's sample code that I would use to try to replace your function:
DatabaseReference database = FirebaseDatabase.getInstance().getReference();
DatabaseReference ref = database.child("users");
Query connectedUser = ref.equalTo(uid);
connectedUser.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot postSnapshot: dataSnapshot.getChildren()) {
// TODO: handle the post here
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
// Getting Post failed, log a message
Log.w(TAG, "loadPost:onCancelled", databaseError.toException());
// ...
}
});
As specified in the Firebase documentation here: https://firebase.google.com/docs/database/android/lists-of-data#filtering_data
in the line : User user= dataSnapshot.getValue(User.class);
you have to put : User user= item.getValue(User.class);
and you have to check the id after you get the user:
if (user.getKey()==uid){
connectedUser.add(user);
}
There are 2 mistakes and a minor issue:
you are using == to compare two String objects. In java, this is true only if they are the same reference. Use equals instead.
addValueEventListener only adds a listener that gets invoked once after you add it and then every time something changes in the value you are listening to: this is an asynchronous behaviour. You are trying to get data synchronously instead. Please read something about this.
you are fetching useless data: you only need an object but you are fetching tons of them. Please consider to use the closest reference you can to the data you are fetching.
So, in conclusion, here's some code. I'd like to point out right now that forcing synchronous acquisition of naturaly asynchronous data is a bad practice. Nevertheless, here's a solution:
public User getConnectedUserByUId(final String uid){
DatabaseReference database = FirebaseDatabase.getInstance().getReference();
DatabaseReference ref = database.child("users").child(uid);
Semaphore sem = new Semaphore(0);
User[] array = new User[1];
ref.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot item: dataSnapshot.getChildren()) {
if (item.getKey()==uid)
{
User user= dataSnapshot.getValue(User.class);
array[0] = user;
}
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
try
{
sem.tryAcquire(10, TimeUnit.SECONDS);
}
catch (Exception ignored)
{
}
return array[0];
}
EDIT: I've just seen that this post is very old. I'm not sure how I ended up here.
Here is my database structure in firebase.
I want to access the message content under messages child.I can get the children count of the messages child ,but cannot retrieve the value of each child.
ref2 points to my firebase instance.
I have to get all the messages from the particulat chatroom.
ref2.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot childDataSnapshot : dataSnapshot.getChildren()) {
listText.add(childDataSnapshot.child("messages").child("message").getValue() + "");
listText.add(childDataSnapshot.child("messages").child("name").getValue() + "");
// userArrayList.add(new User("" + childDataSnapshot.child("username").getValue(), "" + childDataSnapshot.child("profileURL").getValue(), ""));
Log.v("messag_ids", "" + childDataSnapshot.child("messages").child("Kd4TQPrAWsNY1vcid1P").child("message")); //displays the key for the node
}
lvChat.setAdapter(new ChatAdapter(ChatActivity.this, listUsername, listText));
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
if you want to get the message child, we need to traverse like this.
'Kd4TN8fuda6CArtAUo0' -> 'messages' -> 'Kd4TQPrAWsNY1vcid1P'->'message'
Try this :
<yourref>.child('Kd4TN8fuda6CArtAUo0').child('messages').child('Kd4TQPrAWsNY1vcid1P').child('message')
Refer to this link by FireBase team : Common SQL Queries converted for the Firebase Database - The Firebase Database For SQL Developers #4
Your issue is here:
childDataSnapshot.child("messages").child("message")
You are looking for a node called message inside messages and it doesn't exist.
You should first have a reference with the messages node and then traverse all children.
First appoach is to use the methods of DataSnapshot to traverse the children
and access the values use:
ref2.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot childDataSnapshot : dataSnapshot.getChildren()) {
String name = (String) childDataSnapshot.child("name").getValue();
//Do the same for other properties.
}
//......
}
//..
}
Otherwise the second approach is to use the built-in JSON-to-POJO serializer/deserializer.
You can use a Message.class and then use
ref2.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot messageSnapshot: dataSnapshot.getChildren()) {
Message message = messageSnapshot.getValue(Message.class);
}
}
//..
}
Your Message class should be something like:
public class Message {
String name;
String message;
String chatroom;
public Message(){
//default constructor
}
//Getters and setters
//....
}
I have more simple answer :
You will try to access the message node like other nodes like chatpic, owner etc ...
// Ur Database reference is the parent node , when u are trying to access message as the child use the below code :
for(DataSnapshot dataSnapshot1:mainSnapShot.child("message").getChildren()){
Map<?, ?> valuex = (Map<?, ?>) dataSnapshot1.getValue();
if (!TextUtils.isEmpty(valuex.get("message").toString())) {
Log.i("message",valuex.get("message").toString());
}
if (!TextUtils.isEmpty(valuex.get("name").toString())) {
Log.i("name",valuex.get("name").toString());
}
}
I followed the documentation, but no matter what, I cannot figure out how to return all the objects from a single node. For example, I want to return a list of all company objects from the companies node. Once I have that list, I want to parse them all into JSON objects. This is my first time with a NoSQL database so I'm sure that I'm missing something small.
Currently I have:
DatabaseReference companiesRef = FirebaseDatabase.getInstance().getReference("12265");
companiesRef.child("companies").addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
Log.d("Count ", dataSnapshot.getChildren().toString());
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
But it just returns null for the value: DataSnapshot { key = companies, value = null }.
Here's my database:
You create your reference like this:
FirebaseDatabase.getInstance().getReference("12265");
This means that Firebase looks at the root of the database and returns the child 12265 from under there. It does not automatically search the tree for a node with a matching name.
So you'll need to specify the entire path:
FirebaseDatabase.getInstance().getReference("android/users/12265");
Don't add any parameters to your getReference() (let it go to the root of database) and then set the addListenerForSingleValueEvent. And you have not used getvalue() on you datasnapshot as well. Try this code:
DatabaseReference companiesRef = FirebaseDatabase.getInstance().getReference();
// this is the patch that I see from the image that you have attached.
companiesRef.child("telenotes").child("android").child("user").child("12265").child("companies").addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
Log.d("Count ", dataSnapshot.getChildren().getValue().toString());
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});