GROQ query: Include author reference fields across multiple content types

You need to add a projection to your query that includes the author reference. Here's how to modify your query:

*[_type in ["homePage", "page", "article", "case"] && defined(slug.current)]{
  "slug": slug.current,
  author->{
    name,
    image
  }
}

The key changes:

1. Replace the [] with {} - The [] at the end was just selecting the slug values directly. You need a projection (curly braces) to shape the data and include multiple fields.

2. Use the -> operator - This dereferences the author reference, following it to the actual author document and pulling the fields you need.

3. Rename slug for clarity - Since you're now returning an object with multiple fields, I've used "slug": slug.current to make it explicit, though you could also just use slug if you want the whole slug object.

If you want to keep the flat array of just slug strings AND get author data, you'd need to decide on your data structure. Most likely you want something like:

*[_type in ["homePage", "page", "article", "case"] && defined(slug.current)]{
  slug,
  author->{
    name,
    image
  }
}

This returns an array of objects, each containing the full slug object and the dereferenced author data. The -> operator is what makes reference dereferencing work in GROQ projections - it follows the reference and lets you select specific fields from the referenced document.