Resolving internal link references in Sanity queries with Astro

Looking at your query, I can see the issue with how you're trying to resolve internal link references in your Portable Text content. The problem is in the structure of your projection - you have an unnecessary nested check that's preventing proper dereferencing.

Here's the corrected query:

*[_type == "page" && slug == "what-is-veterinary-physiotherapy"]{
    ...,
    content[]{
        ...,
        markDefs[]{
            ...,
            _type == "internalLink" => {
                "slug": @.reference->slug
            }
        }
    }
}

What changed:

1. Removed the nested _type == "reference" check - this was causing the issue
2. Simplified to just @.reference->slug to properly dereference

How it works:

• The @ symbol refers to the current element in the markDefs array (your internalLink object)
• .reference-> follows the reference field using GROQ's dereference operator (->)
• slug grabs the slug field from the referenced document

Important note: If your slug is stored as an object with a current property (which is common in Sanity), you'll need:

*[_type == "page" && slug == "what-is-veterinary-physiotherapy"]{
    ...,
    content[]{
        ...,
        markDefs[]{
            ...,
            _type == "internalLink" => {
                "slug": @.reference->slug.current
            }
        }
    }
}

This pattern is documented in Sanity's guide on joining references in Portable Text. The arrow operator (->) is the key to dereferencing and fetching data from related documents in GROQ queries.

If you need to fetch additional fields from the referenced document (like title, or the entire slug object), you can expand the projection:

markDefs[]{
    ...,
    _type == "internalLink" => {
        "slug": @.reference->slug.current,
        "title": @.reference->title
    }
}