How to use multiple nested dynamic routes with getStaticPaths?

When using getStaticPaths in Next.js, if you have multiple nested dynamic routes, for example, your page directory structure looks like this:

shell
pages
└── posts
    └── [year]
        └── [month]
            └── [slug].js

In this scenario, you must supply parameters for each dynamic route segment ([year], [month], [slug]). Here's an example of getStaticPaths that demonstrates how to generate paths for the above nested route structure:

javascript
export async function getStaticPaths() {
  // Assume you have a function that returns all post data
  const posts = await getAllPosts();

  // Generate paths using post data
  const paths = posts.map((post) => {
    // Ensure year, month, and slug match the dynamic route folder names
    const { year, month, slug } = post;

    return {
      params: {
        year: year.toString(),
        month: month.toString(),
        slug: slug
      }
    };
  });

  return {
    paths,
    fallback: false // Or use 'blocking' or true
  };
}

In the above code, getAllPosts is a hypothetical function that you need to replace based on your data source. It should return an array of all posts, each with year, month, and slug properties.

paths is an array of objects, each with a params key corresponding to the dynamic route parameters. These parameters must be strings, which is why we call toString() in the example to ensure the values are string-formatted.

The fallback key instructs Next.js on how to handle paths not listed in the paths array. If fallback is set to false, any path not in the paths array results in a 404 error. If set to true or blocking, Next.js will attempt to dynamically generate the page.

Note that getStaticPaths runs only during the build phase. Therefore, if your post data is dynamically updated, you need to regenerate the site to update the path list. For fully static incremental generation, consider using fallback: 'blocking'. In production, when a request is made for a path not in paths, Next.js renders the page on the server and caches it for future requests.