How to write a query to sort the Orders according to "Time"?

Question

My database (Firebase Realtime Database) looks like this:

The code I wrote for sorting the orders acc. to Time:

val myRef = FirebaseDatabase.getInstance().getReference("Orders");
myRef.orderByChild("Time").addValueEventListener(orderListener)

But this won't work? I think my argument to orderByChild method is wrong. How to fix this?

Answer 1

In order to be able to get the data, you have to attach a listener on the Query object and iterate through the results as you can see in the following lines of code:

val rootRef = FirebaseDatabase.getInstance().reference
val ordersRef = rootRef.child("Orders")
val queryByTime = ordersRef.orderByChild("Time")
val valueEventListener = object : ValueEventListener {
    override fun onDataChange(dataSnapshot: DataSnapshot) {
        for (ds in dataSnapshot.children) {
            val phone = ds.child("Phone").getValue(String::class.java)
            Log.d("TAG", phone)
        }
    }

    override fun onCancelled(databaseError: DatabaseError) {
        Log.d("TAG", databaseError.getMessage()) //Don't ignore potential errors!
    }
}
queryByTime.addListenerForSingleValueEvent(valueEventListener)

Since your "Time" property is of type String, you may not get the best results, since the ordering is done lexicographically:

• How to order the nodes in firebase console based on key

So the best option the you have is to change the type of the field from String to a number.