How can I check if a value exists already in a Firebase data class Android
<p>I want to check if the bus number already exists in the database of Firebase.</p>
<p>Here's my sample code. I've been searching for the past days but I can't find the right code to do so.</p>
<pre><code>ref = new Firebase(Config.FIREBASE_URL);
postRef = ref.child(&quot;BusNumber&quot;);

busNum = edtBus.getText().toString().trim();
route1 = route.trim();
seat = edtSeat.getText().toString().trim();

if (!busNum.isEmpty() &amp;&amp; !route1.isEmpty() &amp;&amp; !seat.isEmpty()) {
    postRef.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            if (dataSnapshot.child(busNum).exists()) {
                edtBus.setError(&quot;Bus number already exists.&quot;);
                edtBus.setText(&quot;&quot;);
            } else {
                busNumber = new BusNumber();
                busNumber.setBusNum(busNum);
                busNumber.setRoute(route1);
                busNumber.setNumSeat(seat);
                postRef.push().setValue(busNumber);
                edtBus.setText(&quot;&quot;);
                edtSeat.setText(&quot;&quot;);
                Toast.makeText(AddBusActivity.this, &quot;Saving successful!&quot;, Toast.LENGTH_SHORT).show();
            }
        }

        @Override
        public void onCancelled(FirebaseError firebaseError) {
            Toast.makeText(AddBusActivity.this, &quot;Error&quot;, Toast.LENGTH_SHORT).show();
            Toast.makeText(AddBusActivity.this, firebaseError.getMessage(), Toast.LENGTH_SHORT).show();
        }
    });

} else {
    Toast.makeText(AddBusActivity.this, &quot;Please complete the information&quot;, Toast.LENGTH_SHORT).show();
}
</code></pre>
<p>Can somebody help me with this matter? Thanks in advance.
Whether the if statement is correct or not, also my problem is why does the <code>postRef.addListenerForSingleValueEvent</code>...doesn't work? I tried to test some toast message but the message won't pop out.</p>
<p><a href="https://i.stack.imgur.com/mF7u1.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/mF7u1.png" alt="here is my firebase database" /></a></p>