Develop Reference

Firebase Realtime Database comparing value inside the child notes with another child note

I have a database something like this. How I want to compare the value for all users to get most value.
restaurant
-userUid
-stateUid
-restaurantUid
-price = 9
-restaurantUid2
-price = 10
-stateUid2
-restaurantUid3
-price = 2
As you can see the database there, stateUid price is 19 while stateUid2 price is only 2
So, stateUid has the most price. How to compare them and display the most one. Thank you
EDIT:
I have done something like this, and it's error at return. And the value is not working.
exports.calculateTotal = functions.database.ref('/restaurant/{userUid}/{stateUid}/{restaurantUid}')
.onWrite((change, context) => {
// Only edit data when it is first created.
if (change.before.exists()) {
return null;
}
// Exit when the data is deleted.
if (!change.after.exists()) {
return null;
}
//Get id
const restaurantUid = context.params.restaurantUid;
let totalValue = 0;
change.after.forEach(function (item) {
totalValue += item.child('total').val();
});
console.log(totalValue);
return functions.database.ref('/priceTotal/' + restaurantUid).child('total').set(totalValue);
});

Firebase queries work on a flat list of nodes. A query can contain only a single unknown key, the key of the direct child nodes under the location where you query. In your data structure there are multiple levels of unknown keys, which means that you can't query for the highest price across all of them.
What you can do in your current data structure is query across one state for the restaurant with the highest price. That'd look something like:
DatabaseReference ref = FirebaseDatabase.getInstance().getReference("restaurant");
DatabaseReference stateRef = ref.child("userUid").child("stateId");
stateRef.orderByChild("price").limitToLast(1).addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot snapshot: dataSnapshot.getChildren()) {
Log.i(TAG, snapshot.getKey()+": "+snapshot.child("price").getValue(Long.class));
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
throw databaseError.toException();
}
}
But you can't search across all states for a user, or even all users. If you want to allow that, you'll have to store all prices in a flat list, like:
restaurant_prices: {
"restaurantid": {
price: 9,
state: "statid",
user: "userid"
}
}
Also see:
Firebase Query Double Nested
Firebase query if child of child contains a value

int totalPrice = 0;
int greaterPrice = 0;
int temp = 0;
DatabaseRefernce restRef = FirebaseDatabase.getInstance().getReference().child("restaurant").child(userUid);
restRef.addValueEventListener(new ValueEventListener(){
onDataChange(Datasnapshot snapshot) {
for(Datasnapshot snap : snapshot) {
String key = snap.getKey();
//This will return you the keys of stateUid
restRef.child(key).addValueEventListener(new ValueEventListener(){
onDataChanged(DatSnapshot datasnapshot) {
//this for loop will iterate through restaurants of that specific state
for(DataSnapshot snap2 : datasnapshot){
totalPrice += (int) snap2..child("price").getValue();
}
//When this loop ends you will get the total price of all restaurants from that state
}
});
//as u see above I mentioned greater price and temp variable
using simple logic of finding greatest number out of two number save the value of greatest integer to the variable every time you loop through state
}
}
}
);
Use nested for loops to iterate from database like above and calculate your prices
Else what you can do is when you are uploading the data of restos - while uploading prices just make an extra node for total price of city and add price of resto every time you upload new resto

Same initial object's data is being loaded in the variable. (Data is retrieved from Firebase) [duplicate]

This question already has answers here:
How to return DataSnapshot value as a result of a method?
(6 answers)
Closed 4 years ago.
So basically what I'm trying to do is 'get the names of teams from an API. Then based on the name of team, I have already stored team's country flag's image url in the firebase database. So after I get the Team name from the API, I'm trying to get the url of the following team from the database'. The problem I'm facing is 'same Url (url of first team) is being loaded to all team's url'.
JSON Code of handcoded urls of the flags:
{"Country_images_url" : {
"india a" : {
"imageURL" : "url_1"},
"india b" : {
"imageURL" : "url_2" } } }
In this for() loop I'm retrieving team's name from an API:
DatabaseReference database_country_images_url = FirebaseDatabase.getInstance().getReference("Country_images_url");
ArrayList<CricketScore> details = new ArrayList<CricketScore>;
for(int i=0, i< length; i++){
String team_1_name;
String team_2_name; // both this strings are filled with valued obtained from API
String team_1_url = url_of_team(team_1_name); // user-defined method
String team_2_url = url_of_team(team_2_name);
// And then I'm saving this data in an ArrayList
CricketScore live = new CricketScore(team_1_name, team_2_name, team_1_url, team_2_url);
details.add(live);
}
This is the user-defined method:
public String url_of_team(String team){
DatabaseReference db_url = database_country_images_url.child(team.toLowerCase()).child("imageURL");
db_url.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
url = dataSnapshot.getValue(String.class);
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
return url;
}
}
Code works fine but the only prblm I'm getting is that same URL is loaded in Arraylist.
I don't understand what is going wrong. Please help me solve this.

CricketScore live = new CricketScore();
Use setter method to set values here team_1_name, team_2_name.
public String url_of_team(String team){
DatabaseReference db_url = database_country_images_url.child(team.toLowerCase()).child("imageURL");
db_url.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
url = dataSnapshot.getValue(String.class);
//Set the data in object here - team_1_url, team_2_url
details.add(live);
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
return url;
}
}
Try to add data in arraylist as shown above inside the onDataChange()

Get Value from Firebase Database

I need to get the string value from the node passcode in my Firebase database to compare with a user input, but unfortunately I am not able to get the value. This is the link to my firebase database in the below image.
This is my codes below:
final DatabaseReference mDatabase = FirebaseDatabase.getInstance().getReference("pin_code");
mDatabase.addListenerForSingleValueEvent(new com.google.firebase.database.ValueEventListener() {
#Override
public void onDataChange(com.google.firebase.database.DataSnapshot dataSnapshot) {
String rface = (String) dataSnapshot.child("pincode").getValue();
if (rface.equals(userPassword) && !rface.equals("")){
Intent intent = new Intent(PinActivity.this, ProfileActivity.class);
startActivity(intent);
}
else {
if (rface.equals("") || rface.equals(null)){
// Creating new user node, which returns the unique key value
// new user node would be /users/$userid/
String userId = mDatabase.push().getKey();
// creating user object
Pin pin = new Pin(authUserId, userPassword);
mDatabase.child(userId).setValue(pin);
Intent intent = new Intent(PinActivity.this, ProfileActivity.class);
startActivity(intent);
}
else {
Toast.makeText(PinActivity.this,"Invalid PIN code", Toast.LENGTH_SHORT).show();
return;
}
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
This is the json code
{
"pin_code" : {
"id" : "TQYTo1NHNnhPJnOxhe1Vok3U6ic2",
"pincode" : "12345"
}
}

This FirebaseDatabase.getInstance().getReference("pin_code") does not refer to the node you're looking for. Most likely you know the id property, in which case you can get the node with:
DatabaseReference collection = FirebaseDatabase.getInstance().getReference("p...");
Query query = collection.orderByChild("id").equalTo("TQT...ic2");
query.addListenerForSingleValueEvent(new com.google.firebase.database.ValueEventListener() {
#Override
public void onDataChange(com.google.firebase.database.DataSnapshot dataSnapshot) {
for (DataSnapshot child: dataSnapshot.getChildren()) {
String rface = (String) child.child("pincode").getValue();
if (rface.equals(userPassword) && !rface.equals("")){
The changes I made:
On the first line we get the collection: the node under which you want to run a query. You struck out the name of that node in the screenshot, but it's the second line you marked.
In the second line we create a query on the id property of each child node under the collection.
In the onDataChange we added a loop. This is needed because a query against the Firebase Database will potentially have multiple results. So the dataSnapshot contains a list of those results. Even if there is only a single result, the snapshot will contain a list of one result. We loop over dataSnapshot.getChildren() to handle those multiple results.
If there can ever only be one node with the same id, you should consider changing your data structure to use the id as the key of the node. So:
pin_codes
uid1: "pincode1"
uid2: "pincode2"
Your code then becomes significantly simpler, because you don't need to query for the user anymore. You can just directly read from the path:
DatabaseReference user = FirebaseDatabase.getInstance().getReference("pin_codes").child("TQT...ic2");
user.addListenerForSingleValueEvent(new com.google.firebase.database.ValueEventListener() {
#Override
public void onDataChange(com.google.firebase.database.DataSnapshot dataSnapshot) {
String rface = (String) dataSnapshot.getValue();
if (rface.equals(userPassword) && !rface.equals("")){

Try change this:
String rface = (String) dataSnapshot.child("pincode").getValue();
To this:
String rface = (String) dataSnapshot.child("pincode").getValue(String.class);

Use the following::
Object some = dataSnapshot.getValue();
String value = some.toString();

Querying in Firebase with equalTo condition not working

I have database structure like this in Firebase
I want to search a search on this structure based on key number and get the parent key in return. Meaning if i search for 8860124421 then i should get -KTEtSR7chN8te1WaW-W in return .
I am doing it like this in android -
final String number = "8860124421";
DatabaseReference global_user_entry_ref = ApplicationContext.getGlobalDataBaseReference()
.child("User-Entry-2").getRef(); //Reference to User-Entry-2
Query query = global_user_entry_ref.orderByChild("number").equalTo(number);
query.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if(dataSnapshot != null){
for(DataSnapshot friend: dataSnapshot.getChildren()){
String firebase_id = (String) friend.getKey();
Log.d("ContactSync","handle number "+firebase_id+" "+number+" "+friend);
}
Log.d("ContactSync","handle number outer "+dataSnapshot);
//user exist
}
else {
//user_does_not_exist
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
Log.d("ContactSync","handle number oncancel "+databaseError.getMessage());
}
});
But I am not getting proper result , dataSanpshot in onDataChange looks like this -
DataSnapshot { key = User-Entry-2, value = null }
but i want to get dataSnapShot with parent of number key.
Please help , Thanks in advance

As #Frank van Puffelen stated in comments , the problem was that i was comparing a number from code with a string in the database , which does not match , Therefore the solution is to change
final String number = "8860124421";
to
final long number = 8860124421;

Firebase orderByChild in android; can't get it to work

I have data structure as:
https://law-apps-44h221543638e.firebaseio.com/apps to promote/0/ >> name:"First App", package:"fra"
https://law-apps-44h221543638e.firebaseio.com/apps to promote/1/ >> name:"Second App", package:"sca"
https://law-apps-44h221543638e.firebaseio.com/apps to promote/2/ >> name:"Third App", package:"tha"
and I query it using
Firebase myFirebaseReference = new Firebase("https://law-apps-44h221543638e.firebaseio.com/apps to promote");
Query queryRef = myFirebaseReference.orderByChild("name");
queryRef.addListenerForSingleValueEvent(new ValueEventListener() { // override methods })
But it returns the data in the same order i.e sorted by the first child (1,2,3, etc.)
How should I query it so it sorts the data by the "name" tag of each child?

Ok so I found the answer to this question and I am writing it so others may benefit from it. I was using an older technique wherein I was finding from datasnapshot my apps using their parents' numbers and due to this, I was delibrately undoing the ordering.
Now I have used dataSnapshot.getChildren().iterator() and it is now working correctly. Here's the code:
Query queryRef = myFirebaseReference.orderByChild("name");
queryRef.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
String name;
String my_package;
long lengthOfForLoop = dataSnapshot.getChildrenCount();
Iterator<DataSnapshot> child = dataSnapshot.getChildren().iterator();
for (int i = 0; i < lengthOfForLoop; i++) {
DataSnapshot next = child.next();
name = next.child("name").getValue(String.class);
my_package = next.child("package").getValue(String.class);
// do something with this data.
}
}
});
}

thanks, Usman!
I used the same code with the children iterable collection in a for loop.
This code was worked for me (in Kotlin):
accountsReference.child(accountId).child("actions").orderByChild("actionPosition").addListenerForSingleValueEvent( object : ValueEventListener {
override fun onDataChange(var1: DataSnapshot) {
if (var1.children != null) {
for (actionsEntries in var1.children) {
...
}
}