title: print out firebase child values
body: <p>I want to look through Firebase and check if a certain value for a child exists and if that value does not exist. I want to print out a statement</p>
  
  <pre><code> databaseRef.child("books").queryOrdered(byChild: "Category").queryEqual(toValue: categorySegue).observe(.childAdded, with: { (snapshot) in
  
              if snapshot.exists() {
                  print("data found")
              }else{
                  print("no data found")
              }
  })
  </code></pre>
  
  <p>When the child value exists, it prints out data found perfectly fine but when it does not exist. It does not print out no data found</p>