Joining on the client

Client side joins are fairly straight-forward, however for newcomers it's often unclear how exactly to go about it. So let's illustrate how it's done.

Example data

We have two collections named: Books & Authors; and here's how our documents look:

Book

{
  _id: 'vJSWRcJATAPyCj9nq',
  authorId: 'YzP8SX8x8GsDD3DQj',
  name: 'On the Origin of Species'
}

Author

{
  _id: '6ciawd8J7mvxPdKFg',
  name: 'Charles Darwin'
}

Templates

<template name="books">  
  <ol>
    {{#each books}}
      {{> book}}
    {{/each}}
  </ol>
</template>

<template name="book">  
  <li>{{name}} by {{author.name}}</li>
</template>  

Helpers

Template.books.helpers({  
  books: function() {
    return Books.find();
  }
});

Template.book.helpers({  
  author: function() {
    return Authors.findOne(this.authorId);
  }
});

More

https://atmospherejs.com/package/collection-helpers
Collection helpers allows you to create helper functions against your collections.