How to extract URL from referenced schema in Sanity?

The issue you're experiencing is expected behavior - reference fields in Sanity only store the _ref and _type by default. To get the actual data from the referenced document (including any URL/slug fields), you need to dereference the reference in your GROQ query using the -> operator.

Here's how to resolve your linkToNews reference:

*[_type == "yourDocumentType"] {
  ...,
  linkToNews->
}

The -> operator tells GROQ to fetch the full referenced document. So if your nouvelles document has a slug field, you'll now get access to it.

If you only need specific fields from the referenced document (like just the slug for building a URL), you can be more selective:

*[_type == "yourDocumentType"] {
  ...,
  linkToNews->{
    title,
    slug
  }
}

Or if you need to construct a full URL path:

*[_type == "yourDocumentType"] {
  ...,
  "newsUrl": "/news/" + linkToNews->slug.current
}

The reference access operator documentation has more details, but the key takeaway is: references are just pointers until you explicitly dereference them with -> in your queries.

If you're working with arrays of references, you'd do:

{
  newsLinks[]->
}

This pattern works whether you're querying from the CLI, using the HTTP API, or fetching data in your frontend with @sanity/client or framework integrations like next-sanity.