Frontmatter provides a Rails template handler for views ending in .yaml or .yml which contain "frontmatter" that is valid YAML contained between two sets of ---, such as:

---
author: Caleb Hearth
website: https://calebhearth.com
likes:
- Dogs
- Frontmatter
- Rails
dislikes:
- Beets
---

This frontmatter is parsed and made available as getter methods in a model you define per "collection" of views. This collection might be "posts" or "talks" and conceptually it can be considered similarly to an ActiveRecord::Base subclass, but with the view file as the data source rather than a database.

A simple use case would be to import blog posts into Rails from a Jekyll site. The code to do that might look like the below. Note that the semantics are very familiar to anyone who's used Rails applications for similar purposes.

class Post < ActionPost::Base
end

ActionPost::Base provides class-level "all" and "find(slug)" methods which list all pages and finds the first page matching the slug. It also extracts all frontmatter and provides it as getter methods such as post.title.

A controller is required, but there is no need to define the default actions. Default index and show actions are provided that list all posts (all files in app/views/posts with a .yaml or .yml extension) and finds posts based on their "slug" which is the filename without any extensions.

class PostsController < Frontmatter::BaseController
end

The ActionPost::Base subclass is inferred to be the singular of the Controller's class name without "Controller", so PostsController would render Post objects and look for views in app/views/posts. The class-level renders_page method overrides this:

class PostsController < Frontmatter::BaseController
  renders_page :blog_post # BlogPost objects / app/views/blog_posts views.
end

resources :posts, only: %i(index show)

This original Jekyll file would be called _posts/2020-05-30-my-first-post.md and would not have a date field in the frontmatter. That would need to be migrated manually or scripted. Date extraction from filename is not a feature of Frontmatter.

---
title: My First Post
date: 2020-05-30
---

Look at all the things I'm not doing!

<h1><%= @page.title %></h1>
<aside><%= time_tag @post.date %></aside>
<%= page_content @page %>

<h1>My Posts</h1>
<ul><% @posts.each do |post| %>
  <li><%= link_to @post.title, post_path(@post) %></li>
<% end %></ul>

Add this line to your application's Gemfile:

gem 'frontmatter'

And then execute:

$ bundle

Or install it yourself as:

$ gem install frontmatter