从方法调用回调访问meteor Template.instance().data

Question

I have such piece of code im meteor template manager:

"click #refuse": function() {
Meteor.call("removeUserFromEvent", this._id, Meteor.userId());
if (Template.instance().data.participants.length === Template.instance().data.orderedParticipants.length) {
  Meteor.call("updateEventStatus", this._id, "ordered");
}
Router.go("/");

}

And I would like to make that if(...){...} stuff executed in a Meteor.call(...) callback, like

"click #refuse": function() {
Meteor.call("removeUserFromEvent", this._id, Meteor.userId(), function(){
  if (Template.instance().data.participants.length === Template.instance().data.orderedParticipants.length) {
  Meteor.call("updateEventStatus", this._id, "ordered");
}
});
Router.go("/");
}

But if I try to do this it turns out that inside of that callback Template.instance() returns null and I can't get data from the template.

How can I put such stuff (I mean, get some current state parameters and depending on those call or not call another method) in method callback? Maybe Template.instance().data is a wrong place for storing state parameters? Is Template.instance.data reactive at all? Maybe I should change the architecture somehow to make it possible for such functionality to reside in a callback?

Answer 1

That's a event handler and event handler functions accept event and template as parameters as in 'event target': function(event, template) {} therefore your code could be revised as:

"click #refuse": function(evt,tmp) {
  // get and cache your template data context references;
  var participants = tmp.data.participants;
  var orderedParticipants = tmp.data.orderedParticipants;

  // this._id is not reliable, you should use Blaze.getData() on the event target
  var _id = Blaze.getData(event.currentTarget)._id;

  var userId = Meteor.userId();

  // make sure your callback function accepts error and result 
  Meteor.call("removeUserFromEvent", _id, userId, function(err,res) {

    if (err) {/* handle error */}

    if (res) {

      if (participants.length === orderedParticipants.length) {

        Meteor.call("updateEventStatus", _id, "ordered", function(err,res) {

          if (err) {/* handle error */}

          if (res) {
            // perhaps you would like to redirect to home after successful operation only
            Router.go("/");
          }

        });
      }

    }

  });

}

PS: There are too many callbacks here, so you may want to look into promises to simplify this code.