title: Firebase with ReactJs: TypeError: this.Ref.orderBy is not a function
body: <p>Hello i'm tying to query specific data from my Firebase by using the <code>oderBy</code> and the <code>equalTo</code> function, but it gives me this error, does anybody know what i'm doing wrong ?  </p>
  
  <pre><code>constructor(props) {
         super(props);
         this.Ref = firebase.database().ref().child('app').child('cards');
       }
  
       componentWillReceiveProps (){
         this.Ref.orderBy('address').equalTo(this.props.city)
            .on('child_added', snap =&gt; {
              console.log(snap)
            })
       }
  </code></pre>