title: Firebase: use email ID as a key
body: <p>While modeling with Firebase readtime DB, stuck with deciding unique key.</p>
  
  <p>My users collection is identified as email ID.<br>
  So my aim is modeling DB such as below.</p>
  
  <pre><code>{
    "users": {
      "aa@dd.com": {
        "name": "aa",
        "addr": "new york",
        "tel": "3224323"
      },
      "bb@dd.com": {
        "name": "bb",
        "addr": "new york",
        "tel": "3224323"
      },
      "cc@dd.com": {
        "name": "bb",
        "addr": "new york",
        "tel": "3224323"
      },
      "dd@dd.com": {
        "name": "cc",
        "addr": "new york",
        "tel": "3224323"
      }
    }
  }
  </code></pre>
  
  <p>But Firebase doesn't allow some special character as it's key.  such as <code>@</code>, <code>:</code>, etc.</p>
  
  <p>How can I fix my modeling to adapt for Firebase?</p>