firebase orderbychild descending code example

Example 1: firebase order by key descending

firebase.database().ref('books').orderByChild('ups').limitToLast(2)

Example 2: firebase orderbychild update

database.ref('/app/posts')
  .orderByChild('material')
  .equalTo(materialName)
  .once('value', function (snapshot) {
    snapshot.forEach(function(child) {
      child.ref.update({material: false});
    });
});