title: How to order database list asc or desc
body: <p>I am trying to query an ordered list in ionic3 and Angularfire2. </p>
  
  <p>By this query it show me the restaurants from lowest to highest rating but how can I query from high to low?</p>
  
  <p>the query:</p>
  
  <pre><code>this.restaurantsRef = afDb.list('/restaurants', ref =&gt; ref.orderByChild('rating'));
  </code></pre>
  
  <p>And how can I do a multiple query? As the user wants to filter the restaurants on multiple conditions.</p>
  
  <p>AngularFire version:</p>
  
  <pre><code>"angularfire2": "^5.0.0-rc.6",
  </code></pre>
  
  <p>The documentation says this:</p>
  
  <pre><code>// Order descending by numbers or strings
  afs.collection('people', ref =&gt; ref.orderBy('age', 'desc') )
  afs.collection('people', ref =&gt; ref.orderBy('name', 'desc') ) // reverse alphabetical
  </code></pre>
  
  <p>But when I try <code>orderBy</code> it returns me this error:</p>
  
  <pre><code>ref.orderBy is not a function
  </code></pre>
  
  <p>OrderBy seems not to exist on type Reference</p>
  
  <p>Could someone help me out?</p>