title: Prevent duplicate entry firebase database
body: <p>I have been making mobile application for iOS and Android platforms and want to prevent this duplicate entries which the apps make. I don't want to this on app side as I'll have to do it on both the platforms.
  Then I heard about the rules in the Firebase Database section and I tried couple of them but didn't work out for me.
  Please help me with the firebase rules.</p>
  
  <p><a href="https://i.stack.imgur.com/L4vYu.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/L4vYu.png" alt="enter image description here"></a></p>