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How can we get the key of the current user from the realtime database when the key of the user is the username in KOTLIN

The code
This is our code, we just want to display the current user's key, that's it so how should we do that.
Currently, the code gives the output of all the keys and not the current user key.
As output, we are getting the values: Asif, Test24, and Vaishnavi in the variable key
The image is of the Realtime Database The image of Realtime Database

To solve this issue, you need to use a query. In Kotlin, the code should look like this:
val uid = FirebaseAuth.getInstance().currentUser?.uid
val db = FirebaseDatabase.getInstance().reference
val usersRef = db.child("Users")
val queryByUid = usersRef.orderByChild("uid").equalTo(uid)
val valueEventListener = object : ValueEventListener {
override fun onDataChange(dataSnapshot: DataSnapshot) {
for (ds in dataSnapshot.children) {
val key = ds.getKey()
Log.d("TAG", key)
}
}
override fun onCancelled(error: DatabaseError) {
Log.d("TAG", error.getMessage()) //Never ignore potential errors!
}
}
queryByUid.addListenerForSingleValueEvent(valueEventListener)
If for example,e the authenticated user is Asif, then the result in the logcat will be:
KYGf ... uSP2
Always remember to add all necessary keys when you create a reference. Never use .child(""), which is an empty string.

How to order data from firebase using timestamp in android in Kotlin

I need to order items from firebase by timestamp. Then I would like to sum the total price so far I have managed to list the products inside a recyclerview, but they are not ordered
private fun getProductData(){
dref = FirebaseDatabase.getInstance().getReference("Products")
dref.addValueEventListener(object : ValueEventListener {
override fun onDataChange(snapshot: DataSnapshot) {
if (snapshot.exists()){
for (productSnapshot in snapshot.children){
val product = productSnapshot.getValue(ProductData::class.java)
productList.add(product!!)
}
prodList.adapter = productAdapter
}
}
override fun onCancelled(error: DatabaseError) {
Toast.makeText(activity, error.message, Toast.LENGTH_SHORT).show()
}
})
if someone can help me order them, and if possible show me how to find the sum of the price. I have read many docs but they don't ring the bell.

To order the child nodes you'll want to use a query as shown in the documentation on ordering and filtering data:
dref = FirebaseDatabase.getInstance().getReference("Products")
val query = dref.orderByChild("prodTime")
query.addValueEventListener(object : ValueEventListener {
...

how to get some child list from Firebase android kotlin?

How i can read just color item in the image with out all data sub child?
I try this
val database = FirebaseDatabase.getInstance()
val personalDataReference = database.getReference("user personal data")
val messageList = ArrayList<String>()
personalDataReference.addValueEventListener(object : ValueEventListener{
override fun onDataChange(dataSnapshot: DataSnapshot){
messageList.add(dataSnapshot.value.toString())
}
override fun onCancelled(error: DatabaseError) {
// Failed to read value
Log.w(TAG, "Failed to read value.", error.toException())
}
})
but it get all the data

Consider using the Firebase Kotlin SDK by GitLive.
This library is also multi-platform, so the same code can be used on both Android and on iOS via Kotlin Multiplatform Mobile.
The code to read the keys from Firebase realtime database would look like this:
val keys = db.reference("/path/to/user personal data")
.valueEvents
.first()
.children
.mapNotNull { it.key }
Note here that valueEvents is a Kotlin Flow of DataSnapshot, therefore you can do more than simply taking the first snapshot and mapping it to a list as shown above. See the Flow documentation.

The things you've marked yellow are known as keys in Firebase terms.
To get a list of only the keys, you can do:
personalDataReference.addValueEventListener(object : ValueEventListener{
override fun onDataChange(dataSnapshot: DataSnapshot){
for (childSnapshot in dataSnapshot.children) {
messageList.add(childSnapshot.key)
}
}
Note that this will still read all JSON from the database, but the list will only contain the keys.

how to check if firebase have value1 and value2 exist

I'm trying to do the following in my Android application using Kotlin :
I have the Firebase data structure as shown in this image:
The user is able to choose 2 stations from the stations included in the data, either as "start_station", "end_station" or "station_number".. in the next function am trying to take the user's selections and check if both are encluded in the same line.
private fun fetchingLinesData(
theEndStation: String,
theStartStation: String,
) {
val database = FirebaseDatabase.getInstance()
val myRef = database.getReference("line")
myRef.addValueEventListener(object : ValueEventListener {
override fun onCancelled(p0: DatabaseError) {
toast(getString(R.string.could_not_find_a_way))
}
override fun onDataChange(p0: DataSnapshot) {
p0.children.forEach{
//Here should be the line that checks if both data exist
}
}
})
}
Tried using This hasChild Method but it wasn't right.

Try to convert your response to HashMap and search using containsValue
override fun onDataChange(p0: DataSnapshot) {
p0.children.forEach {
//Here should be the line that checks if both data exist
if(it.hasChildren()) {
val stationLines = it.value as HashMap<String, Any>
val validStart = stationLines.containsValue(theStartStation)
val validEnd = stationLines.containsValue(theEndStation)
...
}
}
}

You can do a query:
myRef.orderByChild("end_station").equalTo(theEndStation).addValueEventListener
This will retrieve the data according to the query, then inside onDataChange() after the forEach you can do the following:
if(p0.exists()){
// retrieve data here
}
Using exists() you can check if the datasnapshot exists.
This query will only check for end_station, if you want to check both, then after the query inside the if statement you can retrieve the first_station:
if(p0.exists()){
val firstStation = it.child("start_station").value
And check if firstStation is equal to theStartStation

why firebase display data randomly and unordered?

i don't know why when i get my data from the firebase will Display on the listview random and unordered i tryed many time with out any result
there is no problem with the data on fire base but on the phone display.
fun AddToList(){
mRef.child("MyPosts").child("TEST").addValueEventListener(object
:ValueEventListener{
override fun onCancelled(p0: DatabaseError?) {
Toast.makeText(this#NewsList,"Error",Toast.LENGTH_SHORT).show()
}
override fun onDataChange(datap0: DataSnapshot?) {
try {
var td = datap0!!.value as HashMap<String,Any>
MyList.clear()
for (key in td.keys){
var data = td[key] as HashMap<String,Any>
MyList.add(ForList(
data["pic"] as String
,data["txt1"] as String
,data["txt2"] as String
,data["m1"] as String
,data["m2"] as String
,data["m3"] as String
)
)
adapter!!.notifyDataSetChanged()
}
}catch (ex:Exception){
Log.e("MyAPP","Error on you app 0000",ex)
}
}
})
}

You're not asking for the data in any specific order: mRef.child("MyPosts").child("TEST").addValueEventListener(.... If you want the data in a specific order, you will have to specify that. For example, to get the child nodes in the order of their keys:
mRef.child("MyPosts").child("TEST").orderByChild().addValueEventListener(...
With this the DataSnapshot that is passed into onDataChange will contain the data in the order of the keys. But if you then get the value like this datap0!!.value as HashMap<String,Any> you are dropping any ordering information, since a map can't maintain the information about the ordering of the child nodes.
To process the data in the order you requested you should look over the child nodes of the DataSnapshot with:
override fun onDataChange(snapshot: DataSnapshot?) {
MyList.clear()
for (child: DataSnapshot? in snapshot.getChildren()) {
var data = child!!.value as HashMap<String,Any>
...