Issue with subscriptions on multiple instances of a template

问题

Here is the scenario. I have a template that contains a #each loop and renders an instance of a particular template, setting the data context on each template as per the docs.

<template name = 'live'>
<div class = 'row'>
    {{#each runways}}
        <div class = 'col-md-2'>
            {{> runway_panel}}
        </div>
    {{/each}}
</div>

</template>

And this is the helper backing it:

Template.live.helpers({
    runways: function(){
        return Runway_Data.find();
    }
});

This works, my issue is as follows. Each live_event_log instance has a template level subscription that subscribes to a publication that takes the _id parameter of the data context, like so:

Template.runway_panel.onCreated(function(){
    var instance = this;
    instance.autorun(function(){
        var subscription = instance.subscribe('runway_status', this.data._id);
    });

    instance.status = function(){
        return Runway_Status.find();
    }

});

This is the publication:

Meteor.publish('runway_status', function(runway){ 

    if(this.userId){
        //Retrieve the last know status for the given runway

        return Runway_Status.find({runway: runway});  
    }

});

This is when it all falls apart, I get this on the browser console:

 [Log] Exception in queued task: http://localhost:3000/client/views/live/runway_panel.js?4efaac87b39527d3dfd3d65a174520f9bce3c565:4:73 (meteor.js, line 888)_withTemplateInstanceFunc@http://localhost:3000/packages/blaze.js?a5c324925e5f6e800a4c618d71caf2848b53bf51:3476:16
http://localhost:3000/packages/blaze.js?a5c324925e5f6e800a4c618d71caf2848b53bf51:1864:54
_withCurrentView@http://localhost:3000/packages/blaze.js?a5c324925e5f6e800a4c618d71caf2848b53bf51:2197:16

As soon as I comment out the subscription line everything else works, am I missing something really obvious here? Could it have something to do with multiple subscriptions to the same publication?

Thank you! :)

SOLUTION

Thanks to Jeremy S. input and some sleep after a night shift i've finally figured it out without an autorun. So here it goes for posterity:

Template.runway_panel.onCreated(function(){
    var self = this;
    self.subscribe('runway_status', this.data._id);
});

Should probably have tried getting some sleep before trying again!

回答1:

The problem is with this.data._id in your subscription, which right now is scoped to the innermost function. You want instance.data._id (which is nonreactive so you wouldn't need an autorun) or Template.currentData() (which is reactive).

Template.runway_panel.onCreated(function(){
    var instance = this;
    instance.autorun(function(){
        var data = Template.currentData();
        var subscription = instance.subscribe('runway_status', data._id);
    });
});

Also note that in your publication, you should mark it as this.ready() if this.userId is undefined. But that's not the source of the error.

回答2:

First, userId is a function and userId() would return current user id. And you could check here to learn more detail of instance.subscribe.

I think your problem may happen in getting runway._id in Meteor.publish

Template.runway_panel.onCreated(function(){
  var instance = this;
  // instance subscribe data whose _id is runwayPanelId
  instance.autorun(function(){
    var dataContext = Template.currentData();
    var subscription = instance.subscribe('runway_status', dataContext.runwayPanelId);
  });

  instance.status = function(){
    return Runway_Status.find();
  }
});

// publication
Meteor.publish('runway_status', function(runway){ 
  // using Meteor.userId() to get current user id
  if(Meteor.userId()){
      //Retrieve the last know status for the given runway
      return Runway_Status.find({runway: runway});  
    }
});

---

<template name = 'live'>
  <div class = 'row'>
    {{#each runways}}
      <div class = 'col-md-2'>
        {{> runway_panel runwayPanelId=_id}}
      </div>
    {{/each}}
  </div>

</template>

来源：https://stackoverflow.com/questions/32690094/issue-with-subscriptions-on-multiple-instances-of-a-template