title: Firebase Database - Retrieve Multiple Entries
body: <p>My data is denormalized and uses a reverse index like suggested by the firebase team. Something similar to:</p>
  
  <pre><code>{
    "users": {
      "alovelace": {
        "name": "Ada Lovelace",
        // Index Ada's groups in her profile
        "groups": {
           // the value here doesn't matter, just that the key exists
           "techpioneers": true,
           "womentechmakers": true
        }
      },
      ...
    },
    "groups": {
      "techpioneers": {
        "name": "Historical Tech Pioneers",
        "members": {
          "alovelace": true,
          "ghopper": true,
          "eclarke": true
        }
      },
      ...
    }
  }
  </code></pre>
  
  <p>Now I want to load all of Ada's groups. I can easily get a list of the group IDs that she belongs to since it's part of her user object.</p>
  
  <p>Is there a way for me to query all of Ada's specific groups by ID at once? Or do I need to create a <code>ValueEventListener</code> per group ID and request each group separately?</p>
  
  <p>On the security side - let's assume that every group is only readable by its members, so I can't query all groups and sort them after the fact.</p>