Meteor Upload to AWS S3 - meteor

Question

I have a Meteor app in which I insert a document (title, description, customer, ...) into a database. The app is using Autoform, Simple Schema and Collection2. I now want to add the possibility to upload a file to S3.
To keep things simple, I would present a filepicker as part of the 'Create Document' and once the file is uploaded, the URL field (from Autoform), should show the URL of the document on S3 (once uploaded) so that the URL is eventually stored in the document collection when the create button is clicked. I realise there might be better ways, but wanted to keep things simple for now.
I have tried to combine the tutorial here. The upload to S3 works, but I fail to get the URL for the uploaded file stored documents collection. The below screenshot shows the layout. Any idea's?
My current code can be found here.

Answer 1

There appear to be autoform add-on packages that specifically address S3 file upload (see the "Files" section here), but since you seem to be using this as learning opportunity, I'll try to explain how I'd do it using core meteor.
But first, before I forget, your uploader template is a child of #autoForm but has a form element of it's own. I think that will cause the generated HTML to have nested form elements (which is no-no). To fix that, I'd move the {{/autoForm}} before the {{> uploader}} and add an event handler for your submit button that submits the form using $('#documentForm').submit(). Note: I haven't tested that.
Now, on to your actual question. You are essentially asking how to modify something in a template (the value of the url field) from an event in a nested template (the uploader template). I'd do that as follows:
When an instance of the parent template is created, attach a ReactiveVar to it that will hold the URL of the uploaded file.
Template.adminDocumentNew.onCreated(function () {
this.url = new ReactiveVar();
});
Provide a helper to get the reactive var.
Template.adminDocumentNew.helpers({
url: function () {
return Template.instance().url;
}
});
Use the helper to set the value in the form.
{{> afQuickField name='url' value=url.get}}
Pass the reactive var to the uploader template as the data context:
{{> uploader urlVar=url}}
Use the reactive var to set the URL when the upload finishes (somewhere in upload-to-amazon-s3):
template.data.urlVar.set(url);
I've created a meteorpad that demonstrates the basic idea outside of the context of autoform and S3.