title: How to get all child's data in firebase database?
body: <p>I have this firebase database </p>
  
  <p><a href="https://i.stack.imgur.com/bbSQl.png"><img src="https://i.stack.imgur.com/bbSQl.png" alt="enter image description here"></a></p>
  
  <p>and i need to get all phone numbers of users , which listener shall i use to get all childes?</p>
  
  <p>Every user is added as an object with user-ID as a name of that object, I need to retrieve this objects without knowing that user-ID </p>
  
  <p>I searched the documentation , it's related to <code>DataSnapshot</code> but i couldn't get a <code>DataSnapshot</code> without a listener ! is it correct to seek a DataSnapshout or shall i use something else </p>