Add Generate Types For A Content Collection as an Astro TIL

astro/generate-types-for-a-content-collection.md

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+# Generate Types For A Content Collection
+
+Let's say I'm using Astro to publish posts via markdown. One of the best ways
+to do that is as a _Content Collection_. The posts will live in `src/content`
+probably under a `posts` directory. Plus a config file will define the
+collection and specify validations for the frontmatter.
+
+```typescript
+// src/content/config.ts
+import { defineCollection, z } from 'astro:content';
+
+const postsCollection = defineCollection({
+  schema: z.object({
+    title: z.string(),
+    description: z.string(),
+    tags: z.array(z.string())
+  })
+});
+
+export const collections = {
+  'posts': postsCollection,
+};
+```
+
+When I first add this to my project and get the collection, it won't know what
+the types are.
+
+```astro
+---
+import { getCollection } from "astro:content";
+
+export async function getStaticPaths() {
+  const blogEntries = await getCollection("posts");
+  //    ^^^ any
+
+  return blogEntries.map((entry) => ({
+    params: { slug: entry.slug },
+    props: { entry },
+  }));
+}
+---
+```
+
+I can tell Astro to generate a fresh set of types for things like content
+collections by running the [`astro sync`
+command](https://docs.astro.build/en/reference/cli-reference/#astro-sync).
+
+```bash
+$ npm run astro sync
+```
+
+This updates auto-generated files under the `.astro` directory which get pulled
+in to your project's `env.d.ts` file.
+
+All of these types will also be synced anytime I run `astro dev`, `astro
+build`, or `astro check`.