Develop Reference

How to get values from different child in firebase realtime database?

Here is my Database architecture where Jobs is the main child and under that there will be users child, and an user can post multiple time. now i want to get all the posts done by all the users at once. is it possible to do that?
https://i.stack.imgur.com/DT3MO.jpg
setQuery(FirebaseDatabase.getInstance().getReference().child("Jobs")
Used that query to get all of the posts from all of the users but didnt work. any better solution for this problem?
setQuery(FirebaseDatabase.getInstance().getReference().child("Jobs").child("Uid");
this one works but cant use this one because i want to set free for all users to read data.

You can do the following:
DatabaseReference reference = FirebaseDatabase.getInstance().getReference("Jobs");
reference.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot ds : dataSnapshot.getChildren()){
String key = ds.getKey();
for (DataSnapshot childSnapshot: ds.getChildren()) {
// get the child attribute under the random key
}
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
throw databaseError.toException();
}
});
Since you have a reference to node Jobs then in the first iteration you can get the random keys (highlighted in your image), and in the second iteration you can get the attributes inside those keys.

Android & Firebase : How can i get data from frebase by key

Firebase database structure
Please how i can get data from firebase with IMEI of the phone.
How i can get listcarte by the phone TPEID!!

If the value you're looking for is always in 0/TPEID, then you can use a query to find the nodes that contains that value with:
DatabaseReference ref = FirebaseDatabase.getInstance().getReference(...);
Query query = ref.orderByChild("0/TPEID").equalTo("869688030960688");
query.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot tpeSnapshot: dataSnapshot.getChildren()) {
System.out.println(tpeSnapshot.getKey()); // Tpe0
System.out.println(tpeSnapshot.child("0/TPEID").getValue(String.class)); // 869688030960688
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
throw databaseError.toException();
}
}
If the value is not at a fixed path under each child, you won't be able to search for it with a Firebase query. In that case, see Firebase Query Double Nested, firebase get url by nested child id for tree like, Firebase query if child of child contains a value

Retrieve Firebase data who have specific child

Please check my database image. I want to select and display all users who have parent = chris
my database image

To retrieve the users that contain parent : chris, you can do the following:
DatabaseReference reference = FirebaseDatabase.getInstance().getReference("users");
reference.orderByChild("parent").equalTo("chris").addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot datas: dataSnapshot.getChildren()){
String name = datas.child("name").getValue(String.class);
String key = datas.getKey();
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
throw databaseError.toException();
}
});
orderByChild.equalTo is a query that will retrieve all the nodes that contain parent equal to chris.

Since you tagged this as a android studio question I assume you are using the Firebase SDK.
You should check out the documentation, where they explain how you can query in a lot of languages with very nice examples.

How to retrieve child data under 2 random keys

How do I display the RequestsID on a recyclerview only when stallID = 1?
How should my DatabaseReference be?
update:

Your database structure would not support orderByChild() from top node. So you would have to set your database reference upto the node food and then you can use orderByChild() query to find the Childs with certain stallID.
This, in code would look something like this:
DatabaseReference ref = FirebaseDatabase.getInstance().getReference().child("Requests").child("1542..").child("foods");
ref.orderByChild("stallID").equalTo(stallIDYouWant).addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
for (DataSnapshot ds : dataSnapshot.getChildren()){
// do here what you wanted
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
// ToDo: don't ignore this, do something for errors
}
)};
This would in fact not help you much because you'd have to set this for every unique id in your database structure.
So the better thing to do here would be make your database structure different. To know more how to make your structure good for this operation, refer this answer.

Firebase DatabaseReference filter by specified values

Lets suppose I have this firebase JSON structure:
And I need to get all the questions which have the atribute "from" equal to "this".
I know that I can use Volley to make a StringRequest and GET all values from my questions.json. Then, in the client side I could iterate over the response and remove the ones which don't have the correct atribute, but this would only work if I have a few questions. If I have millions of questions I would need to iterate over those millions of questions.
Is there any way I could put a filter on my request to get only the question with an attribute of my choice? (Ex: search questions.json where from == this)

Try this if may be useful in your scenario
DatabaseReference reference = FirebaseDatabase.getInstance().getReference();
Query query = reference.child("questions").orderByChild("from").equalTo("this");
query.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()) {
for (DataSnapshot issue : dataSnapshot.getChildren()) {
// do with your result
}
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});

You can use equalTo
Query query = reference.child("questions").orderByChild("from").equalTo("this");