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Search firebase database for key and check if it contains expected value

I want to use the user id of the user object to check if the role value is equal to employee, but I am not sure how to do that. I know how to get the user id but the rest i am unaware of. My database looks like this:
-User
-userid
firstName:John
lastName:Wall
role:Employee
- userid
firstName:Bradley
lastName:Beal
role:Patient

You need to do a query:
DatabaseReference ref = FirebaseDatabase.getInstance().getReference("User");
ref.orderByChild("role").equalTo("Employee").addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot ds : dataSnapshot.getChildren()){
String name = ds.child("firstName").getValue(String.class);
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
throw databaseError.toException();
}
});
First add reference to node User then use orderByChild() to retrieve the name of the users that have role equal to Employee.

firebase data change method in android studio

how email's value change from "app-user/users"?
Firebase state :
this isn't web language, i use javacode and xml of androidstudio.
i'm tryed under code.
databaseReference.child(app-user).child(user).orderByChild("email").equalTo("user4~~")
I don't know what to do next.

To get all users whose email address starts with user4:
DatabaseReference usersRef = FirebaseDatabase.getInstance().getReference().child("app-users/users");
Query usersQuery = usersRef.orderByChild("email").startAt("user4").endAt("user4\uF7FF");
usersQuery.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot userSnapshot: dataSnapshot.getChildren()) {
System.out.println(userSnapshot.getKey()+": "+userSnapshot.getChild("displayName").getValue(String.class));
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
throw databaseError.toException();
}
}
To understand the usersRef.orderByChild("email").startAt("user4").endAt("user4\uF7FF") query, read it as:
Take all child nodes of usersRef and order them by their email property.
Then find the first child node that starts with user4.
Then return each child node, until you find a child that starts with .endAt("user4\uF7FF") (or further).
In this the \uF7FF is no magic code, but just the last known Unicode character. So by combining .startAt("user4").endAt("user4\uF7FF"), you're building a startsWith operator.

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.

Android Studio firebase get key of child with specific value

I have am developing an app in Android Studio and I am using FireBase to store data. Lets say I have a node that has multiple children, I would like to get the key of the child that has a specific value. For example;
I would like to read from the node 'languages', the key of the child with value 'English' so that I get 'eng'. Note that upfront I do not know that the key is 'eng'!
Someone knows a way to achieve this, without importing all the children?

Try something like this:
DatabaseReference ref = FirebaseDatabase.getInstance().getReference().child("languages");
ref.orderByValue().equalTo("English").addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot snap : dataSnapshot.getChildren()) {
String value = snap.getValue(String.class);
String key = snap.getKey();
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});

I can't get the key of firebase database

In my solution I save data from Windows form application. There is no problem. I can list them in my android app. On this point I am trying to get key value to update the data, but always I get null.
FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference myReference = database.getReference();
Query myTopPostsQuery = myReference.child("DURUSLAR").orderByChild("kayitid").equalTo("1298843637");
myTopPostsQuery.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot postSnapshot: dataSnapshot.getChildren())
{
//Childadi =postSnapshot.getKey().toString();
String anahtar=postSnapshot.getKey().toString();
Toast.makeText(getApplicationContext(),anahtar,Toast.LENGTH_LONG);
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
Can you please help me?

When you execute a query at a location in the Firebase Database, it will search for the property you order/filter on in each child under that location. Since you query in /DURUSLAR, Firebase looks for /DURUSLAR/{something}/kayitid. Such a property does not exist, since you only have /DURUSLAR/{something}/{pushid}/kayitid.
To fix this problem you have two options:
query at a lower level
query to the property at its (fixed) path
The first option is to create the query at a lower level in the tree:
Query myTopPostsQuery = myReference.child("DURUSLAR/K6").orderByChild("kayitid").equalTo("1298843637");
Now the query is looking for /DURUSLAR/{pushid}/kayitid and it will work.
The second option is to query for the known path of the property:
Query myTopPostsQuery = myReference.child("DURUSLAR").orderByChild("K6/-KknsAR4_KFAeZ1HVXPW/kayitid").equalTo("1298843637");
It seems unlikely you want this here, but the approach may be helpful in other situations. Often when you need this approach with push IDs in the path, you'll want to look at http://stackoverflow.com/questions/40656589/firebase-query-if-child-of-child-contains-a-value.

The reason you are getting null is because you are doing orderByChild on the wrong level of data . According to your data u need to have a child K4-> which has a unique_id_push_id -> kayitid.Therefore you need to traverse the K4 in order to get 1298843637 for key kayitid.You can follow this tutorial to understand the retrieving of data from firebase .
Query myTopPostsQuery = myReference.child("DURUSLAR").child("k6").orderByChild("kayitid").equalTo("1298843637");
myTopPostsQuery.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot postSnapshot: dataSnapshot.getChildren())
{
//Childadi =postSnapshot.getKey().toString();
String anahtar=postSnapshot.getKey().toString();
Toast.makeText(getApplicationContext(),anahtar,Toast.LENGTH_LONG);
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});