Waiting for template render in Meteor, inconsistent - templates

Question

Been scratching my head on this, so here's the simplest way to view it - I'm using this:
Template.today.rendered = function() {
console.log(this.firstNode.children.length);
};
Simply to try and get the count of items that are supposedly rendered. The template looks like:
<template name="today">
<div class="todaySlider">
{{#each dayOfWeek}}
{{> singleDay}}
{{/each}}
</div>
</template>
and if it's of any importance, singleDay looks like:
<template name="singleDay">
<div class="day {{isCurrent}}">
<h2 class="date">{{date}}</h2>
{{#each items}}
{{> item }}
{{/each}}
</div>
</template>
I'm trying to wait for all the "singleDays" to render, however that count I'm logging is usually different on refresh. I'll get anything from 0 to the correct value, and I don't understand why. This seems to be the right place to call it, I fear that maybe the double "each" is too slow?
I've tried timers (which I honestly shouldn't) and even DOM Mutation Observers (which seem like overkill) but surely there is a pure Meteor approach to this, any ideas?

Answer 1

Template.rendered happens when the template is rendered, but that doesn't mean there'll be any data in it.
I'm pretty sure you'll need to do this inside a helper.
each helpers don't have to return cursors, they can also return an array. If the number of "singleDays" is short, you could send an array to the template instead of a cursor. It's kind of ugly, and there might be a better way to do this, but I think this will work.
Template.today.helpers({
dayOfWeek: function() {
var days = DaysCollection.find({}).fetch();
if (days[days.length - 1]) days[days.length - 1].isLast = true;
return days;
}
});
I assume {{isCurrent}} is where you add the extra class that you're talking about. If so, just have the isCurrent helper look for this.isLast to be true.

Answer 2

Seems like what is happening here is that the template is being rendered before the Mongo collection is sent to the client. To be more specific, meteor renders your template as fast as possible, which means that it has no concept of 'waiting' for any data to be sent from the server to the client. Therefore, if you place anything indirectly regarding database queries inside of a non-reactive call (Template.rendered), then it will execute with the data as undefined.
I'm assuming your dayOfWeek helper looks something like this:
Template.today.helpers({
daysOfWeek: function () {
var today = CollectionName.findOne();
return today.daysOfWeek;
}
})
(Or maybe you are using the router to pass the day directly to the template)
Either way, within your router you need to wait for the Mongo collection item to be sent to the client before any rendering takes place. If you are using Iron-Router, you simply have to 'wait' for your data/subscription.
More information can be found here: https://github.com/iron-meteor/iron-router/blob/devel/Guide.md#wait-and-ready
If you are still using autopublish, then you can replace the subscription with your database query.