Jekyll linked documents in collections?

Question

In Jekyll's Front Matter, is there a way to make references to another document?

I have a custom collection, and would like to add meta-data in each document such as "parent-topic" (a link to the parent), and "children" (an array of documents), or "related-topics".

With such a reference I could access the linked documents' meta-data, such as their title, url, or other arbitrary data.

The idea is a hierarchy of documentation, with topics, sub-topics, sub-sub-topics, etc. And a topic page could show a list of child topics, or a breadcrumb for the parent topics, etc.

Answer 1

Real question that deserve a real answer. I also got this documentation problem. Following advise from Ben Balter, I started to use collections. The idea was to make

• a table of content reflecting topic/sub-topics arrangement,
• a breadcrumb on each page

I gave up because it was simplest to code against pages. So, here's how I do documentation with pages.

Prerequisites :

• documentation is in a folder eg : documentation

• permalink is set to pretty in _config.yml

• folders hierarchy describes documentation organization

example

documentation
|--index.html
|--chapter-1
|  |--index.html
|
|--chapter-2
|  |--index.html
|  |
|  |--part-1
|  |  |--index.html
|  |  |--subpart-1
|  |     |--index.html
|  |--part-2
|  |  |--index.html
|  |
|  |--part-3.html

Note : documentation/chapter-2/part-2/index.html can also be documentation/chapter-2/part-2.html, because permalink is set to pretty, generated page will be at documentation/chapter-2/part-2/index.html.

• Pages at a same level are sorted depending on a weight front matter variable. This can be anything you want. Numbering by tenth allows easy insertion for new doc.

example front matter

---
title: My title
weight: 10
---

• documentation get default variables values from _config.yml

example

defaults:
  -
    scope:
      path: "documentation"
      type: pages

    values:
      isDoc: true # allows quick extraction from site.pages
      layout: page

Once those prerequisites are in place, it's easy to print a table of content and a breadcrumb.

Table of content

_includes/show-children.html

{% assign parentDir = include.dir %}
{% if parentDir == nil %}<h1>You must specify a root directory</h1>{% endif %}

{% assign allDocs = include.docs %}
{% if allDocs == nil %}{% assign allDocs = site.pages | sort: "weight" %}{% endif %}

{% assign level = include.level %}
{% if level == nil %}{% assign level = parentDir | remove_first: "/" | split:"/" | size %}{% endif %}

{% assign maxLevel = include.maxLevel %}
{% if maxLevel == nil %}{% assign maxLevel = 100 %}{% endif %}

{% assign nextLevel = level | plus : 1 %}

{% comment %}+++++++++++++++++++++++++++++++++++++++++++++++++
Looking for all page in this path with the same level (siblings)
This avoid to deep recursion and error like :
__ Liquid Exception: Nesting too deep __
+++++++++++++++++++++++++++++++++++++++++++++++++{% endcomment %}

{% assign siblings = "" | split: "/" %}
{% for s in allDocs %}
    {% assign sPageLevel = s.url | remove_first: "/" | split:"/" | size %}
    {% if sPageLevel == level and s.url contains parentDir %}
        {% if s.title %}{% assign siblings = siblings | push: s %}{% endif %}
    {% endif %}
{% endfor %}

<ul>
{% for p in siblings %}
    <li><a href="{{site.baseurl}}{{p.url}}"{%if p.url == page.url%} class="active"{%endif%}>{{ p.title }}</a>
    {% if nextLevel <= maxLevel %}
      {% include show-children.html dir=p.dir docs=allDocs level=nextLevel maxLevel=maxLevel %}
    {% endif %}
    </li>
{% endfor %}
</ul>

{% comment %}+++++++++++++++++++++++++++++++++++++++++++++++++
Because all variables are globales (all includes have the same scope)
we restore level and nextLevel variables to parent values
+++++++++++++++++++++++++++++++++++++++++++++++++{% endcomment %}
{% assign level = level | minus : 1 %}
{% assign nextLevel = nextLevel | minus : 1 %}

Use

This include can be called with several arguments :

dir : root dir to explore (ie : /documentation)

docs : an array of pages - default to site.pages

level: level at which we start printing (/documentation is at level 1, /documentation/chapter-1 is at level 2, and so on) Default to 'dir' level

maxLevel: where to stop to print - default to 100

Extracting documentation pages
{% assign documents = site.pages | where: "isDoc", true | sort: "weight" %}
{% assign dir = "documentation" %}

This will print all documentation hierachy
{% include show-children.html dir=dir docs=documents %}

This will start printing at level 2
{% include show-children.html dir=dir docs=documents level=2 %}

This stop printing at level 2
{% include show-children.html dir=dir docs=documents maxLevel=2 %}

On page layout if you just want to print page children you can do :

{% assign documents = site.pages | where: "isDoc", true | sort: "weight" %}
{% assign level = page.dir | remove_first: "/" | split:"/" | size %}
{% assign childrenLevel = level | plus : 1 %}
{% include show-children.html docs=documents dir=page.dir level=childrenLevel %}

Breadcrumb

_includes/breadcrumb.html

{% assign minLevel = include.minLevel %}
{% if minLevel == nil %}{% assign minLevel = 1 %}{% endif %}

<div class="breadcrumb">
<p>You are here : </p>
{% assign documents = site.pages | where: "isDoc", true | sort: "weight" %}
{% include get-parents.html page=page minLevel=minLevel docs=documents %}
<p>{{ page.title }}</p>
</div>

<style type="text/css">
.breadcrumb p { display: inline; }
.breadcrumb p+p+p:before { content:"» "; }
</style>

_includes/get-parents.html

{% assign currentPage = include.page %}
{% assign minLevel    = include.minLevel %}
{% assign allDocs     = include.docs %}
{% assign pageLevel   = currentPage.dir | remove_first: "/" | split:"/" | size %}
{% assign parentLevel = pageLevel | minus: 1 %}
{% if parentLevel >= minLevel %}
    {% for p in allDocs %}
        {% assign pPageLevel = p.dir | remove_first: "/" | split:"/" | size %}
        {% if pPageLevel == parentLevel and currentPage.dir contains p.dir %}
            {% include get-parents.html page=p minLevel=minLevel docs=allDocs %}
            <p><a href="{{site.baseurl}}{{p.url}}">{{ p.title }}</a></p>
        {% endif %}
    {% endfor %}
{% endif %}

Use

Print Documentation > chapter 1 > part 1

{% include breadcrumb.html %}

Print Chapter 1 > part 1

{% include breadcrumb.html minLevel=2 %}

Can it be more simple ?

Working code can be found here.