Polymer feed value into second dom-repeat - polymer

Question

I'm trying to use a dom-repeat inside a dom-repeat over a json array inside a json array. How can pass a value from the first array over to the second dom-repeat?
To illustrate, I have the following json array which loads fine:
"books": [
{
"title": "book1",
"slug": "b1",
"authors": ["author1","author2"],
"blurb": "Some text"
},
{
"title": "book2",
"slug": "b2",
"authors": ["author2","author3"],
"blurb": "some more text"
}]
I'm iterating over the array 'books' and retrieve title and blurb. Then underneath, I want both authors of each book listed and I also want a link to each one in the format of /slug/author (f.i. /b1/author1). But because in the second dom-repeat I redefine "items", the 'slug' is no longer available. How do I go about this?
<template>
<iron-ajax
auto
url="somelist.json"
handle-as="json"
last-response="{{someList}}"></iron-ajax>
<template is="dom-repeat" items="{{someList.books}}">
<paper-collapse-group>
<paper-collapse-item header$="{{item.title}}">
<p>{{item.blurb}}</p>
</paper-collapse-item>
<template is="dom-repeat" items="{{item.authors}}">
<a href$="/[[slug]]/[[item]]">{{item}}</a></div>
</template>
</paper-collapse-group>
</template>
</template>
I'm also very new to Polymer so thank you for helping me learn!

Answer 1

Use the as attribute to use a custom name for the item property.
Example:
<template>
<iron-ajax
auto
url="somelist.json"
handle-as="json"
last-response="{{someList}}"></iron-ajax>
<template is="dom-repeat" items="{{someList.books}}" as="book">
<paper-collapse-group>
<paper-collapse-item header$="{{book.title}}">
<p>{{book.blurb}}</p>
</paper-collapse-item>
<template is="dom-repeat" items="{{book.authors}}" as="author">
<a href$="/[[book.slug]]/[[author]]">{{author}}</a></div>
</template>
</paper-collapse-group>
</template>
</template>

Answer 2

So what you can do is to create another element, let's say that would look like:
<dom-module id="authors">
<template>
<template is="dom-repeat" items="[[authors]]">
<a href$="/[[slug]]/[[item]]">[[item]]</a>
</template>
</template>
<script>
Polymer({
is: 'authors',
properties: {
authors: Array,
slug: String
},
});
</script>
</dom-module>
and then inject it into your code like:
<template is="dom-repeat" items="[[someList.books]]">
<paper-collapse-group>
<paper-collapse-item header$="[[item.title]]">
<p>[[item.blurb]]</p>
</paper-collapse-item>
<authors slug="[[item.slug]]" authors="[[item.authors]]"></authors>
</paper-collapse-group>
</template>