title: Angular Firebase: Property 'database' does not exist on type
body: <p>I am trying to use the firebase.database.reference in my Angular project but I cannot get rid of the follow errors even after searching the web.  </p>
  
  <p>I am getting the error "Property 'database' does not exist" for the following line</p>
  
  <pre><code>let dbRef = firebase.database().ref('students/');
  </code></pre>
  
  <p>Also, I got the error for "Cannot find name 'firebase' so I added </p>
  
  <pre><code>import * as firebase from '@firebase/app';
  </code></pre>
  
  <p>this removed the 'firebase' name error but I wonder if this is the best way to import firebase?</p>
  
  <p>I am using Angular 5</p>
  
  <pre><code>  import { AngularFireDatabase, AngularFireList, AngularFireObject } from 'angularfire2/database';
   "angularfire2": "^5.0.0-rc.4",
   "@angular/common": "5.2.0",
   "@angular/compiler": "5.2.0",
   "@angular/core": "5.2.0",
  </code></pre>