GROQ query not filtering posts by category reference correctly

I can see the issue with your query! The problem is in your filter condition within the subquery. You're comparing category._id (from the post) with ^.categories._ref, but the correct path should be ^._id to reference the parent category's ID.

Here's the corrected query:

*[_type == "category"]{
  _id,
  title,
  "post": *[_type == "post" && references(^._id)]
}

The references() function is actually the cleanest way to handle this. It will find all posts that have a reference to the current category's ID.

Alternatively, if you want to be more explicit about the field path, you can use:

*[_type == "category"]{
  _id,
  title,
  "post": *[_type == "post" && category._ref == ^._id]
}

The key issues with your original query were:

1. You used category._id instead of category._ref - references store the ID in a _ref property
2. You used ^.categories._ref which doesn't exist on the category document - you just need ^._id to access the parent category's ID

The ^ operator allows you to access the parent scope within the subquery, so ^._id refers to the category's _id that you're currently iterating over in the outer query.

If you want to return additional fields from the posts, you can expand the projection:

*[_type == "category"]{
  _id,
  title,
  "posts": *[_type == "post" && references(^._id)]{
    title,
    slug,
    publishedAt
  }
}