How to get specific element and orderby priority in Firebase and Angular

问题

I have a firebase reference like this:

$scope.lessons = $firebaseArray(firebase.child('Lessons').orderByChild('courseID').equalTo($state.params.courseID));

I'm outputting the lessons like this:

<ul>
        <li class="lesson" ng-if="lesson.moduleID == module.$id" ng-repeat="lesson in lessons" lessonid="{{lesson.$id}}">
            <lessonedit></lessonedit>
        </li>
</ul>

I need to order the lessons by priority, but when I add the orderByPriority() function to the end of the firebase reference it says I can only use one orderBy call.

I tried the filter lesson in lessons | orderByPriority but it says that filter does not exist?

回答1:

If Priority is an attribute of lesson, you can use the angular filter orderBy like this:

<ul>
    <li class="lesson" 
        ng-if="lesson.moduleID == module.$id" 
        ng-repeat="lesson in lessons | orderBy:'Priority'" 
        lessonid="{{lesson.$id}}">
        <lessonedit></lessonedit>
    </li>
</ul>

回答2:

Currently, you can't mix .orderByPriority() and .orderByChild() as they are different order by functions.

However, you can still solve your problem by only using .orderByPriority(), if you re-structure your data.

Structuring your data a specific way allows you query your data, as if you could use two orderBy functions.

In your case you have a location of "Lessons" that all have a push-id key of their "lesson id": /lessons/$lessonID.

You could change your structure to key off of the courseId and then the lesson_id: /lessions/$courseID/$lessonID.

The data would look like this:

{
  "lessons": {
    "1": {
      "-K4NQTsjo3iswX4PhKUw": {
        title: "My Course"
      },
      "-K4NAWsjo5iswX4Jk4fa": {
        title: "Another Course"
      }
    }
    "2": {
      "-K4NQTsjo3iswX4PhKUw": {
        title: "My Course"
      },
      "-K4NQPjMZVCoFRYc_1v5": {
        title: "Intro to Data Structure"
      }
    }
  }
}

Now since the key uses the courseID, we can order by by both courseID and priority:

var courseID = $state.params.courseID;
var ref = new Firebase('<my-firebase-app>.firebaseio.com/lessons');
var query = ref.child(courseID).orderByPriority();
var syncArray = $firebaseArray(query);

You can store this in a factory in your AngularJS code.

angular.module('app', ['firebase')
  .constant('FirebaseUrl', '<my-firebase-app>')
  .service('RootRef', ['FirebaseUrl', Firebase])
  .factory('Lessons', Lessons)
  .controller('MainCtrl', MainCtrl);

function Lessons(RootRef) {
  return function Lessons(courseID) {
    var ref = RootRef.child('Lessons');
    var query = ref.child(courseID).orderByPriority();
    return $firebaseArray(query);
  }
}

function MainCtrl($scope, $state, Lessons) {
  var courseID = $state.params.courseID;
  $scope.lessons = Lessons(courseID);
}

回答3:

Using Firebase's new Query API, you can do this with:

var ref = new Firebase('https://your.firebaseio.com/');

ref
  .orderBy('genre')
  .startAt('comedy').endAt('comedy')
  .orderBy('lead')
  .startAt('Jack Nicholson').endAt('Jack Nicholson')
  .on('value', function(snapshot) { 
  console.log(snapshot.val()); 
  });

Note that the new Query API is still in beta, so things may change before it's officially released.

See this jsbin for a similar query on Firebase's sample data set.

You can check the original Post of Frank van Puffelen here

来源：https://stackoverflow.com/questions/33992935/how-to-get-specific-element-and-orderby-priority-in-firebase-and-angular

标签

angularjs

firebase

angularfire