How to query parent data from references in GROQ?

No, references in Sanity do not store parent data - they only store the ID of the referenced document in a _ref field. A reference is essentially just a pointer to another document.

For example, when you have a reference field, it's stored like this:

{
  "_id": "alice",
  "_type": "employee",
  "name": "Alice Anderson",
  "department": {"_ref": "engineering"}
}

Notice that department only contains {"_ref": "engineering"} - no actual department data is stored in the parent document.

Querying References with GROQ

To retrieve the actual referenced document data, you use the dereference operator -> in GROQ:

*[_type == "employee"] {
  name,
  department->
}

This resolves the reference and returns the full department document:

{
  "name": "Alice Anderson",
  "department": {
    "_id": "engineering",
    "_type": "department",
    "name": "Engineering"
  }
}

You can also project specific fields from the referenced document:

*[_type == "employee"] {
  name,
  department->{
    name,
    location
  }
}

Array References

For arrays of references, dereference all items like this:

*[_type == "footer"] {
  socials[]->{
    name,
    url
  }
}

Reverse Lookups

If you need to find documents that reference a specific document (reverse lookup), use the references() function:

*[_type == "artist"][0] {
  name,
  "events": *[_type == "event" && references(^._id)] {
    name
  }
}

This finds all events that reference the current artist.

The key takeaway: references are lightweight pointers that only store IDs, and you use the -> operator to fetch the actual referenced document data when querying.