title: Angular Firebase How to find and retrieve data by field
body: <p>I have datas on realtime Database on firebase with the following structure :</p>
  
  <pre><code>    {   "tests" : [ {
             "description" : "55",
             "number" : "11",
             "serie" : "0"   }, {
             "description" : "22",
             "number" : "13",
             "serie" : "0"   }, {
             "description" : "Test",
             "number" : "55",
             "serie" : "2"   
  } ]
  </code></pre>
  
  <p>And I want tro retrieve all my data where the field "serie" are equal to "0".
  I have a methode in my service component for retrieving all the tests data, like this :</p>
  
  <pre><code>  getTests(){
      firebase.database().ref('/tests')
        .on('value',(data: DataSnapshot)=&gt;{
          this.tests= data.val() ? data.val():[];
          this.emitTests;
        }
      );
    }
  </code></pre>
  
  <p>At this time I do not know how retrieving only datas where serie is equal to 0.</p>