Order documents by referenced field values in Sanity GROQ

This is a classic GROQ challenge! You want to order celebs based on when their related facts were most recently updated. The key is to use a subquery to find each celeb's most recent fact, then sort by that.

Here's the solution from the Stack Overflow thread you posted:

*[_type == "celeb"] {
  _id,
  name,
  "latestFact": *[_type == "fact" && celeb._ref == ^._id] | order(_updatedAt desc)[0]
}
| order(latestFact._updatedAt desc)

How this works:

1. Query all celebs: *[_type == "celeb"] gets all celebrity documents

2. Project with subquery: Inside the projection {}, we create a latestFact field that runs a nested query:

   • *[_type == "fact" && celeb._ref == ^._id] finds all facts where the celeb reference matches the current celeb's _id (the ^ operator references the parent document)
   • | order(_updatedAt desc)[0] sorts those facts by most recent first and takes the first one

3. Sort by the nested field: The outer | order(latestFact._updatedAt desc) sorts all celebs by their most recent fact's update time

This assumes your fact document has a celeb field that's a reference to a celeb document. If your reference field has a different name, just adjust celeb._ref accordingly.

Performance note: This pattern can be expensive on large datasets since it runs a subquery for each celeb. If you need better performance with many documents, consider denormalizing by storing the latest fact timestamp directly on the celeb document and updating it whenever a fact changes (you could automate this with Sanity Functions).