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Collections (using Tags)

While pagination allows you to iterate over a data set to create multiple templates, a collection allows you to group content in interesting ways. A piece of content can be a part of multiple collections, if you assign the same string value to the tags key in the front matter.

A Blog Example

For a blog site, your individual post files may use a tag called post, but it can be whatever you want. In this example, mypost.md has a single tag post:

Syntax Markdown
---
tags: post
title: Hot Take—Social Media is Considered Harmful
---

This will place this mypost.md into the post collection with all other pieces of content sharing the post tag. To reference this collection and make a list of all posts, use the collections object in any template:

Syntax Liquid, Nunjucks
<ul>
{%- for post in collections.post -%}
<li>{{ post.data.title }}</li>
{%- endfor -%}
</ul>
Syntax JavaScript .11ty.js
module.exports = function({collections}) {
return `<ul>
${collections.post.map((post) => `<li>${ post.data.title }</li>`
).join("\n")}
</ul>`;
};

Compare the post.url and special Eleventy-provided page.url variable to find the current page. Building on the previous example:

Syntax Liquid, Nunjucks
<ul>
{%- for post in collections.post -%}
  <li{% if page.url == post.url %} class="active"{% endif %}>{{ post.data.title }}</li>
{%- endfor -%}
</ul>

The Special all Collection

By default Eleventy puts all of your content (independent of whether or not it has any assigned tags) into the collections.all Collection. This allows you to iterate over all of your content inside of a template.

<ul>
{%- for post in collections.all -%}
  <li><a href="{{ post.url }}">{{ post.url }}</a></li>
{%- endfor -%}
</ul>

Option: Exclude content from Collections New in v0.8.0

In front matter (or further upstream in the data cascade), set the eleventyExcludeFromCollections option to true to opt out of specific pieces of content added to all collections (including collections.all, collections set using tags, or collections added from the Configuration API in your config file). Useful for your RSS feed, sitemap.xml, custom templated .htaccess files, et cetera.

Filename excluded.md
---
eleventyExcludeFromCollections: true
tags: post
---
This will not be available in `collections.all` or `collections.post`.

Tag Syntax

You can use a single tag, as in the above example OR you can use any number of tags for the content, using YAML syntax for a list.

A single tag: cat

---
tags: cat
---

This content would show up in the template data inside of collections.cat.

Multiple tags, single line

---
tags: ['cat', 'dog']
---

This content would show up in the template data inside of collections.cat and collections.dog.

Multiple tags, multiple lines

---
tags:
  - cat
  - dog
---

This content would show up in the template data inside of collections.cat and collections.dog.

Collection Item Data Structure

Syntax Liquid, Nunjucks
<ul>
{%- for post in collections.post -%}
  <li>{{ post.data.title }}</li>
{%- endfor -%}
</ul>

Note in the above example that we output the post.data.title value? Similarly, each collection item will have the following data:

{ inputPath: './test1.md',
  fileSlug: 'test1', // fileSlug was added in 0.5.3
  outputPath: './_site/test1/index.html',
  url: '/test1/',
  date: 2018-01-09T04:10:17.000Z,
  data: { title: 'Test Title', tags: ['tag1', 'tag2'], date: 'Last Modified' },
  templateContent: '<h1>This is my title</h1>\n\n<p>This is content…' }

Sorting

The default collection sorting algorithm sorts in ascending order using:

  1. The input file’s Created Date (you can override using date in front matter, as shown below)
  2. Files created at the exact same time are tie-broken using the input file’s full path including filename

For example, assume I only write blog posts on New Years Day:

posts/postA.md (created on 2008-01-01)
posts/postB.md (created on 2008-01-01)
posts/post3.md (created on 2007-01-01)
another-posts/post1.md (created on 2011-01-01)

This collection would be sorted like this:

  1. posts/post3.md
  2. posts/postA.md
  3. posts/postB.md
  4. another-posts/post1.md

Sort descending

To sort descending in your template, you can use a filter to reverse the sort order. For example, in Nunjucks it’d look like this (Liquid also has a reverse filter built in):

<ul>
{%- for post in collections.post | reverse -%}
  <li>{{ post.data.title }}</li>
{%- endfor -%}
</ul>

You should not use Array reverse() on collection arrays in your templates, like so:

{%- for post in collections.post.reverse() -%}

This will mutate the array and re-order it in-place and will have side effects for any use of that collection in other templates.

Instead, use one of the many template engine utilities provided for you to do this, such as Liquid’s reverse or Nunjucks’ reverse

This is a Common Pitfall.

Overriding Content Dates

You can modify how a piece of content is sorted in a collection by changing it’s default date. Read more at Content Dates.

---
date: 2016-01-01
---

Advanced: Custom Filtering and Sorting

To get fancier with your collections (and even do a bit of your own custom filtering, if you’d like), you can use our Configuration API.

Inside of your .eleventy.js config file, use the first argument to the config function (eleventyConfig below) to call the API (note that module exports is a function and not an object literal):

Filename .eleventy.js
module.exports = function(eleventyConfig) {
// API is available in `eleventyConfig` argument

return {
// your normal config options
markdownTemplateEngine: "njk"
};
};

You can use eleventyConfig like so:

Filename .eleventy.js
module.exports = function(eleventyConfig) {

eleventyConfig.addCollection("myCollectionName", function(collection) {
// get unsorted items
return collection.getAll();
});

};

New in v0.8.0 addCollection can accept async functions too. Use await in your callback to do some asynchronous things!

Return values

Collection API Methods

The data collection gets passed to the callback. You can use it in all sorts of ways:

getAll()

Returns an array.

Filename .eleventy.js
module.exports = function(eleventyConfig) {
// Unsorted items (in whatever order they were added)
eleventyConfig.addCollection("allMyContent", function(collection) {
return collection.getAll();
});
};
Filename .eleventy.js
module.exports = function(eleventyConfig) {
// Filter using `Array.filter`
eleventyConfig.addCollection("keyMustExistInData", function(collection) {
return collection.getAll().filter(function(item) {
// Side-step tags and do your own filtering
return "myCustomDataKey" in item.data;
});
});
};
Filename .eleventy.js
module.exports = function(eleventyConfig) {
// Sort with `Array.sort`
eleventyConfig.addCollection("myCustomSort", function(collection) {
return collection.getAll().sort(function(a, b) {
return b.date - a.date;
});
});
};

Curious where the date is coming from? Read more about Content Dates.

Note that the last example adding the myCustomSort collection will be available in your templates as collections.myCustomSort.

getAllSorted()

Returns an array.

Filename .eleventy.js
module.exports = function(eleventyConfig) {
// Use the default sorting algorithm (ascending by date, filename tiebreaker)
eleventyConfig.addCollection("allMySortedContent", function(collection) {
return collection.getAllSorted();
});
};
Filename .eleventy.js
module.exports = function(eleventyConfig) {
// Use the default sorting algorithm in reverse (descending dir, date, filename)
// Note that using a template engine’s `reverse` filter might be easier here
eleventyConfig.addCollection("myPostsReverse", function(collection) {
return collection.getAllSorted().reverse();
});
};

Note that while Array .reverse() mutates the array in-place, all Eleventy Collection API methods return new copies of collection arrays and can be modified without side effects to other collections. However, you do need to be careful ⚠️ when using Array .reverse() in templates!

Filename .eleventy.js
module.exports = function(eleventyConfig) {
// Filter using `Array.filter`
eleventyConfig.addCollection("onlyMarkdown", function(collection) {
return collection.getAllSorted().filter(function(item) {
// Only return content that was originally a markdown file
let extension = item.inputPath.split('.').pop();
return extension === "md";
});
});
};

getFilteredByTag( tagName )

Returns an array.

Filename .eleventy.js
module.exports = function(eleventyConfig) {
// Get only content that matches a tag
eleventyConfig.addCollection("myPosts", function(collection) {
return collection.getFilteredByTag("post");
});
};

getFilteredByGlob( glob )

Returns an array. Will match an arbitrary glob (or an array of globs) against the input file’s full inputPath (including the input directory).

Filename .eleventy.js
New in v0.2.14
module.exports = function(eleventyConfig) {
// Filter source file names using a glob
eleventyConfig.addCollection("onlyMarkdown", function(collection) {
return collection.getFilteredByGlob("**/*.md");
});
};
Filename .eleventy.js
New in v0.2.14
module.exports = function(eleventyConfig) {
// Filter source file names using a glob
eleventyConfig.addCollection("posts", function(collection) {
return collection.getFilteredByGlob("_posts/*.md");
});
};
Filename .eleventy.js
New in v0.2.14
module.exports = function(eleventyConfig) {
// Filter source file names using a glob
eleventyConfig.addCollection("posts", function(collection) {
// Also accepts an array of globs!
return collection.getFilteredByGlob(["posts/*.md", "notes/*.md"]);
});
};

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