How to access metadata when using "where" filter - jekyll

Question

I've got a structured set of pages in a collection, and the structure looks something like this:
chapter1
section1
section2
section3
chapter2
section1
section2
section3
chapter3
section1
section2
section3
Each is a separate page that renders its own permalink.
Say I'd like to make a link to chapter3/section1, how would I do this? I'd like to use the Liquid where filter, but this seems to give me the page contents, not the metadata.
{% assign section_post = site.chapters | where:"url","chapter3/section1" %}
{{ section_post }}
This gets me the proper page, but not the right content. If I were to write this in my layout, I get nothing:
{{ section_post.title }}
What am I doing wrong? How can I get the metadata using a where filter? I've got a bunch of pages, so looping through them is super inefficient...

Answer 1

The problem is that a where expression returns all the objects in an array given a certain condition.
[#<Jekyll::Document _chapters/chapter3/section1 collection=chapters>]
In this case you are expecting that this list of objects just return a single item, so we can select that item with the first liquid tag (returns the first element of an array).
{% assign ch3s1 = site.chapters |
where:"id","/chapters/chapter3/section1" | first%}
title: {{ch3s1.title}}
<br>
url: {{ch3s1.url}}
would output the desired section:
title: Chapter 3 section 1
url: /chapters/chapter3/section1