Dynamic nested route with slug queries returning empty array in Next.js

Looking at your code, I can spot the issue! In your getStaticProps query, you have an extra set of empty brackets [] that's causing problems:

*[_type == "contributionsEcrivain" && defined(slug.current)][] {

That [] after your filter is treating the result as an array and trying to slice it, which is likely returning an empty result. Remove it!

However, there's a bigger issue with your approach: you're fetching ALL contributions documents, not just the specific one for the current route. In getStaticProps, you need to filter by the specific contributions slug from the route params:

export async function getStaticProps({ params }) {
  const { slug, contributions } = params;
  
  const query = groq`
    *[_type == "contributionsEcrivain" && slug.current == $contributionsSlug][0] {
      _id,
      title,
      associatedArtist[0]->{
        "slug": slug.current,
        title,
      },
      associatedNumero[0]->{
        "slug": slug.current,
        number
      },
      body,
      "slug": slug.current,
    }
  `;
  
  const data = await client.fetch(query, { 
    contributionsSlug: contributions 
  });
  
  return {
    props: {
      contribution: data
    }
  };
}

Key changes:

1. Removed the extra [] after the filter
2. Added [0] at the end to get a single document instead of an array
3. Used parameterized query with $contributionsSlug to filter for the specific contribution matching the route
4. Passed the contributions param from the route to the query

You could also verify the artist matches to be extra safe:

*[_type == "contributionsEcrivain" 
  && slug.current == $contributionsSlug 
  && $artistSlug in associatedArtist[]->slug.current][0] {
  // ... rest of projection
}

And pass both slugs: { contributionsSlug: contributions, artistSlug: slug }

Your getStaticPaths logic looks solid - that's correctly building all the possible route combinations. The issue was just in how you were fetching the data for each specific page!