How do I re-run my Meteor publication to refresh the contents of a collection on the client?

Question

I'm creating a quiz app. I want to show a single random question, take the user's answer, show feedback, and move to another random question.

I'm using this to publish a single random question:

getRandomInt = function(min, max) {
  return Math.floor(Math.random() * (max - min + 1) + min);
};

randomizedQuestion = function(rand) {
  // These variables ensure the initial path (greater or less than) is also randomized
  var greater = {$gte: rand};
  var less = {$lte: rand};
  var randomBool = !!getRandomInt(0,1);
  var randomQuestion = Questions.find({randomizer: randomBool ? greater : less }, {fields: {body: true, answers: true}, limit: 1, sort: {randomizer: 1}});

  //  If the first attempt to find a random question fails, we'll go the other direction.
  if (randomQuestion.count()) {
    return randomQuestion;
  } else {
    return Questions.find({randomizer: randomBool ? less : greater}, {fields: {body: true, answers: true}, limit: 1, sort: {randomizer: 1}});
  }
};

Meteor.publish("question", function(rand) {
  if (rand) {
    return randomizedQuestion(rand);
  }
});

I have a route that subscribes to that publication:

Router.route("/", {
  name:"quiz",
  template:"question",
  subscriptions: function() {
    this.questionSub = Meteor.subscribe("question", Math.random());
  },
  data: function() {
    return {
      question: Questions.find(),
      ready: this.questionSub.ready
      };
  }
});

How can I re-run the query with a new value for Math.random() in order to get another random question after the user answers the question?

Answer 1

If you replace Math.random() with a reactive variable, that will cause your subscription to be reevaluated. For simplicity I'll use a session variable in this example.

Somewhere before the route runs (at the top of the file or in a before hook), initialize the variable:

  Session.setDefault('randomValue', Math.random());

Then change your subscription to use it:

  Meteor.subscribe('question', Session.get('randomValue'));

Finally, whenever you want to restart the subscription and update your data context, change the variable again:

  Session.set('randomValue', Math.random());

Note you may want question: Questions.findOne() instead of question: Questions.find() assuming your template needs a document instead of a cursor.