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Front Matter Defaults

Using front matter is the way you specify metadata for the file-based resources for your site, setting things like a default layout, or customizing the title, or providing taxonomy terms.

Sometimes you will find you’re repeating a few configuration options over and over. For example, setting the same layout in each file, adding the same category, etc. You might even want to add author names which are the same for the majority of posts.

There are two ways to accomplish this: the data cascade, and via your site’s configuration file.

The Data Cascade

You can add _defaults.yml (also .yaml or .json) files anywhere in your source tree, which will then cause a “data cascade”. In other words, any resources in that folder or in a subfolder will use the front matter data contained in the defaults file. Defaults files in subfolders can also potentially overwrite values contained in parent folders (hence the term “cascade”).

For example, if you want all “posts” collection resources to have the layout “post” without having to repeatedly write layout: post front matter, simply add _defaults.yml to the src/_posts folder:

layout: post

Now, if you have some posts in a subfolder (let’s say fancy_posts) and you want those posts to use the “fancy_post” layout, you could add a second _defaults.yml file in that subfolder like so:

layout: fancy_post

Now all the fancy_posts posts will use the fancy_post layout. If you had other front matter variables in the parent _defaults.yml in src/_posts, those would carry over to the fancy_posts defaults unless you decide to override them explicitly.

Also, keep in mind these are “default” values, so if you were to add layout: some_other_layout to a post, it would overwrite either layout: post or layout: fancy_post. This is what makes front matter defaults so powerful!

Trick out your collections

Defaults files work well for custom collections! Just add a _defaults.yml to the collection root folder to set layouts and other variables for your entire collection.

Think globally

You can also add a defaults file to src itself! For example, if you wanted every resource on your site to start off with a default thumbnail image, you could simply add image: /images/thumbnail_image.jpg to a defaults file in src and it would apply globally.

Configuration-based Front Matter Defaults

Instead of (or in addition to) the data cascade, you can set front matter defaults in your configuration file using a special rules-based syntax. To do this, add a defaults key to the bridgetown.config.yml file in your project’s root folder.

Let’s say that you want to add a default layout to all pages and posts in your site. You would add this to your bridgetown.config.yml file:

defaults:
  - values:
      layout: "default"

Stop and rerun bridgetown start

The bridgetown.config.yml master configuration file contains global configurations and variable definitions that are read once at execution time. Changes made to bridgetown.config.yml will not trigger an automatic regeneration.

Use Data Files to set up metadata variables and other structured content you can be sure will get reloaded during automatic regeneration.

You probably don’t want to set a layout on every file in your project, so you can also specify a collection value under the scope key.

defaults:
  - scope:
      collection: "posts"
    values:
      layout: "default"

This will only set the layout for resources in the posts collection.

You can set multiple scope/values pairs for defaults.

defaults:
  - scope:
      collection: "pages"
    values:
      layout: "my-site"
  - scope:
      path: "projects" # scopes to a particular path within your source folder
      collection: "pages"
    values:
      layout: "project" # overrides previous default layout
      author: "Ursula K. Le Guin"

With these defaults, all pages would use the my-site layout. Any html files that exist in the projects/ folder will use the project layout, if it exists. Those files will also have the resource.data.author variable set to Ursula K. Le Guin.

collections:
  my_collection:
    output: true

defaults:
  - scope:
      collection: "my_collection"
    values:
      layout: "default"

In this example, the layout is set to default inside the collection with the name my_collection.

Glob patterns in Front Matter defaults

It is also possible to use glob patterns (currently limited to patterns that contain *) when matching defaults. For example, it is possible to set specific layout for each special-page.html in any subfolder of section folder.

collections:
  my_collection:
    output: true

defaults:
  - scope:
      path: "section/*/special-page.html"
    values:
      layout: "specific-layout"

Globbing and Performance

Please note that globbing a path is known to have a negative effect on performance. Globbing a path will increase your build times in proportion to the size of the associated collection directory.

Precedence

Bridgetown will apply all of the configuration settings you specify in the defaults section of your bridgetown.config.yml file. You can choose to override settings from other scope/values pair by specifying a more specific path for the scope.

If you set defaults in the site configuration by adding a defaults section to your bridgetown.config.yml file, you can override those settings in an individual resource’s front matter. For example:

# In bridgetown.config.yml
...
defaults:
  - scope:
      path: "projects"
      collection: "pages"
    values:
      layout: "project"
      author: "Ursula K. Le Guin"
      category: "project"
...
# In projects/foo_project.md
---
author: "John Smith"
layout: "foobar"
---
The post text goes here...

The projects/foo_project.md resource would have the layout set to foobar instead of project and the author set to John Smith instead of Ursula K. Le Guin when the site is built.

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