Tutorial - Extend with Content Collections

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Content collections are a powerful way to manage groups of similar content, such as blog posts. Collections help to organize your documents, validate your YAML frontmatter, and provide automatic TypeScript type-safety for all of your content (even if you don’t write any TypeScript yourself).

ここで学ぶことは…

Move your folder of blog posts into src/data/blog/
Create a schema to define your blog post frontmatter
Use getCollection() to get blog post content and metadata

Prerequisites

You will need an existing Astro project with Markdown or MDX files in the src/pages/ folder.

This tutorial uses the Build a Blog tutorial’s finished project to demonstrate converting a blog to content collections. You can fork and use that codebase locally, or complete the tutorial in the browser by editing the blog tutorial’s code in StackBlitz.

You can instead follow these steps with your own Astro project, but you will need to adjust the instructions for your codebase.

We recommend using our sample project to complete this short tutorial first. Then, you can use what you have learned to create content collections in your own project.

Build a Blog Tutorial Code

In the Build a Blog introductory tutorial, you learned about Astro’s built-in file-based routing: any .astro, .md, or .mdx file anywhere within the src/pages/ folder automatically became a page on your site.

To create your first blog post at https://example.com/posts/post-1/, you created a /posts/ folder and added the file post-1.md. You then added a new Markdown file to this folder every time you wanted to add a new blog post to your site.

Pages vs Collections

Even when using content collections, you will still use the src/pages/ folder for individual pages, such as your About Me page. But, moving your blog posts outside of this special folder will allow you to use more powerful and performant APIs to generate your blog post index and display your individual blog posts.

At the same time, you’ll receive better guidance and autocompletion in your code editor because you will have a schema to define a common structure for each post that Astro will help you enforce. In your schema, you can specify when frontmatter properties are required, such as a description or an author, and which data type each property must be, such as a string or an array. This leads to catching many mistakes sooner, with descriptive error messages telling you exactly what the problem is.

Read more about Astro’s content collections in our guide, or get started with the instructions below to convert a basic blog from src/pages/posts/ to src/data/blog/.

Test your knowledge

Which type of page would you probably keep in src/pages/?
1. Blog posts that all contain the same basic structure and metadata
2. Product pages in an eCommerce site
3. A contact page, because you do not have multiple similar pages of this type
Which is not a benefit of moving blog posts to a content collection?
1. Pages are automatically created for each file
2. Better error messages, because Astro knows more about each file
3. Better data fetching, with a more performant function
Content collections uses TypeScript…
1. To make me feel bad
2. To understand my project, even if I don’t write any TypeScript
3. Only if I have the strict or strictest configuration set

Extending the blog tutorial with content collections

The steps below show you how to extend the final product of the Build a Blog tutorial by creating a content collection for the blog posts.

Upgrade dependencies

Upgrade to the latest version of Astro, and upgrade all integrations to their latest versions by running the following commands in your terminal:
- npm
- pnpm
- Yarn
Terminal window
# Upgrade Astro and official integrations together npx @astrojs/upgrade
Terminal window
# Upgrade Astro and official integrations together pnpm dlx @astrojs/upgrade
Terminal window
# Upgrade Astro and official integrations together yarn dlx @astrojs/upgrade
The blog tutorial uses the base (least strict) TypeScript setting. In order to use content collections, you must set up TypeScript for content collections either by using the strict or strictest setting, or by adding an option in tsconfig.json.

In order to use content collections without writing TypeScript in the rest of the blog tutorial example, add the following two TypeScript configuration options to the config file:
tsconfig.json
```
{
  // Note: No change needed if you use "astro/tsconfigs/strict" or "astro/tsconfigs/strictest"
  "extends": "astro/tsconfigs/base",
  "compilerOptions": {
    "strictNullChecks": true,
  }
}
```

Create a collection for your blog posts

Create a new collection (folder) called src/data/blog/.
Move all your existing blog posts (.md files) from src/pages/posts/ into this new collection.

Create a src/content/config.ts file to define a schema for your postsCollection. For the existing blog tutorial code, add the following contents to the file to define all the frontmatter properties used in its blog posts:

// Import the glob loader
import { glob } from "astro/loaders";
// Import utilities from `astro:content`
import { z, defineCollection } from "astro:content";
// Define a `loader` and `schema` for each collection
const blog = defineCollection({
    loader: glob({ pattern: '**\/[^_]*.md', base: "./src/data/blog" }),
    schema: z.object({
      title: z.string(),
      pubDate: z.date(),
      description: z.string(),
      author: z.string(),
      image: z.object({
        url: z.string(),
        alt: z.string()
      }),
      tags: z.array(z.string())
    })
});
// Export a single `collections` object to register your collection(s)
export const collections = { blog };

In order for Astro to recognize your schema, quit the dev server (CTRL + C) and run the following command: npx astro sync. This will define the astro:content module. Restart the dev server to continue with the tutorial.

Generate pages from a collection

Create a page file called src/pages/posts/[...slug].astro. Your Markdown and MDX files no longer automatically become pages using Astro’s file-based routing when they are inside a collection, so you must create a page responsible for generating each individual blog post.

Add the following code to query your collection to make each blog post’s slug and page content available to each page it will generate:

---
import { getCollection } from 'astro:content';

export async function getStaticPaths() {
  const posts = await getCollection('blog');
  return posts.map(post => ({
    params: { slug: post.id }, props: { post },
  }));
}

const { post } = Astro.props;
const { Content } = await render(post);
---

Render your post <Content /> within the layout for Markdown pages. This allows you to specify a common layout for all of your posts.

---
import { getCollection } from 'astro:content';
import MarkdownPostLayout from '../../layouts/MarkdownPostLayout.astro';

export async function getStaticPaths() {
  const posts = await getCollection('posts');
  return posts.map(post => ({
    params: { slug: post.id }, props: { post },
  }));
}

const { post } = Astro.props;
const { Content } = await render(post);
---
<MarkdownPostLayout frontmatter={post.data}>
  <Content />
</MarkdownPostLayout>

Remove the layout definition in each individual post’s frontmatter. Your content is now wrapped in a layout when rendered, and this property is no longer needed.
src/content/posts/post-1.md
```
---
layout: ../../layouts/MarkdownPostLayout.astro
title: 'My First Blog Post'
pubDate: 2022-07-01
...
---
```

Replace `import.meta.glob()` with `getCollection()`

Anywhere you have a list of blog posts, like the tutorial’s Blog page (src/pages/blog.astro/), you will need to replace Astro.glob() with getCollection() as the way to fetch content and metadata from your Markdown files.

---
import { getCollection } from "astro:content";
import BaseLayout from "../layouts/BaseLayout.astro";
import BlogPost from "../components/BlogPost.astro";

const pageTitle = "My Astro Learning Blog";
const allPosts = Object.values(await import.meta.glob("../pages/posts/*.md", { eager: true }));
const allPosts = await getCollection("blog");
---

You will also need to update references to the data returned for each post. You will now find your frontmatter values on the data property of each object. Also, when using collections each post object will have a page slug, not a full URL.

---
import { getCollection } from "astro:content";
import BaseLayout from "../layouts/BaseLayout.astro";
import BlogPost from "../components/BlogPost.astro";

const pageTitle = "My Astro Learning Blog";
const allPosts = await getCollection("blog");
---
<BaseLayout pageTitle={pageTitle}>
  <p>This is where I will post about my journey learning Astro.</p>
  <ul>
    {
      allPosts.map((post) => (
        <BlogPost url={post.url} title={post.frontmatter.title} />)}
        <BlogPost url={`/posts/${post.id}/`} title={post.data.title} />
      ))
    }
  </ul>
</BaseLayout>

The tutorial blog project also dynamically generates a page for each tag using src/pages/tags/[tag].astro and displays a list of tags at src/pages/tags/index.astro.

Apply the same changes as above to these two files:

fetch data about all your blog posts using getCollection("blog") instead of using import.meta.glob()
access all frontmatter values using data instead of frontmatter
create a page URL by adding the post’s slug to the /posts/ path

The page that generates individual tag pages now becomes:

---
import { getCollection } from "astro:content";
import BaseLayout from "../../layouts/BaseLayout.astro";
import BlogPost from "../../components/BlogPost.astro";

export async function getStaticPaths() {
  const allPosts = await getCollection("blog");
  const uniqueTags = [...new Set(allPosts.map((post) => post.data.tags).flat())];

  return uniqueTags.map((tag) => {
    const filteredPosts = allPosts.filter((post) =>
      post.data.tags.includes(tag)
    );
    return {
      params: { tag },
      props: { posts: filteredPosts },
    };
  });
}

const { tag } = Astro.params;
const { posts } = Astro.props;
---

<BaseLayout pageTitle={tag}>
  <p>Posts tagged with {tag}</p>
  <ul>
    { posts.map((post) => <BlogPost url={`/posts/${post.id}/`} title={post.data.title} />) }
  </ul>
</BaseLayout>

Try it yourself - Update the query in the Tag Index page

Import and use getCollection to fetch the tags used in the blog posts on src/pages/tags/index.astro, following the same steps as above.

Show me the code.

---
import { getCollection } from "astro:content";
import BaseLayout from "../../layouts/BaseLayout.astro";
const allPosts = await getCollection("blog");
const tags = [...new Set(allPosts.map((post) => post.data.tags).flat())];
const pageTitle = "Tag Index";
---
...

Update any frontmatter values to match your schema

If necessary, update any frontmatter values throughout your project, such as in your layout, that do not match your collections schema.

In the blog tutorial example, pubDate was a string. Now, according to the schema that defines types for the post frontmatter, pubDate will be a Date object.

To render the date in the blog post layout, convert it to a string:
src/layouts/MarkdownPostLayout.astro
```
...
<BaseLayout pageTitle={frontmatter.title}>
 {frontmatter.pubDate.toString().slice(0,10)}
 {frontmatter.description}
 Written by: {frontmatter.author}
 <img src={frontmatter.image.url} width="300" alt={frontmatter.image.alt} />
...
```

Update RSS function

Lastly, the tutorial blog project includes an RSS feed. This function must also use getCollection() to return information from your blog posts. You will then generate the RSS items using the data object returned.

import rss from '@astrojs/rss';
import { pagesGlobToRssItems } from '@astrojs/rss';
import { getCollection } from 'astro:content';

export async function GET(context) {
  const posts = await getCollection("blog");
  return rss({
    title: 'Astro Learner | Blog',
    description: 'My journey learning Astro',
    site: context.site,
    items: await pagesGlobToRssItems(import.meta.glob('./**/*.md')),
    items: posts.map((post) => ({
      title: post.data.title,
      pubDate: post.data.pubDate,
      description: post.data.description,
      link: `/posts/${post.id}/`,
    })),
    customData: `<language>en-us</language>`,
  })
}

For the full example of the blog tutorial using content collections, see the Content Collections branch of the tutorial repo.

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Tutorial - Extend with Content Collections

Prerequisites

Build a Blog Tutorial Code

Pages vs Collections

Test your knowledge

Extending the blog tutorial with content collections

Upgrade dependencies

Create a collection for your blog posts

Generate pages from a collection

Replace `import.meta.glob()` with `getCollection()`

Try it yourself - Update the query in the Tag Index page

Update any frontmatter values to match your schema

Update RSS function

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Tutorial - Extend with Content Collections

Prerequisites

Build a Blog Tutorial Code

Pages vs Collections

Test your knowledge

Extending the blog tutorial with content collections

Upgrade dependencies

Create a collection for your blog posts

Generate pages from a collection

Replace import.meta.glob() with getCollection()

Try it yourself - Update the query in the Tag Index page

Update any frontmatter values to match your schema

Update RSS function

Replace `import.meta.glob()` with `getCollection()`