title: Querying Firebase Users to Check If Contact Exists in Database
body: <p>I am currently setting up a Firebase app and am able to retrieve a list of all users who use the app. When a user first signs up for the app they are required to confirm their phone number as most iOS apps do these days. I am storing their phone number in the "users" node. <strong>My question is how do I query in Firebase to check to see if that phone number exists within my database? Basically I want to query against a list of phone numbers that I'm generating against the list of all contacts</strong> </p>
  
  <p>This will allow me to display if a specific contact is currently using the app, it will show up underneath the contact name in a tableview / collectionview. If they aren't then they could receive an invite to join the app via text / email. </p>
  
  <p>The "users" node is displayed in my Firebase database as the following: </p>
  
  <pre><code>    "users" : {
      "userId1" : {
          "name" : "Alex",
          "email" : "alex@gmail.com",
          "phoneNumber" : "123456789" 
      },  
      "userId2" : {
          "name" : "Ben",
          "email" : "ben@gmail.com",
          "phoneNumber" : "223456789" 
  
      },
      "userId3" : {
          "name" : "Charles",
          "email" : "charles@gmail.com",
          "phoneNumber" : "323456789" 
  
      }
  }
  </code></pre>
  
  <p>I am new to querying in a nosql database and would appreciate the help. Thank you so much! </p>