Grails: Use results of Criteria + projections as a filter on the original table

Question

I have the following table/model:

class Post {
  int id;
  String comment;
  static belongsTo = [category_id:Category];
}

I wish to create a query that can filter out the last Post (highest id) per Category. I want the results in List<Post> form.

In other words (I believe) in SQL the query would look as follows:

SELECT *
FROM
  Post AS source
  JOIN (
    SELECT MAX(id) AS id, category_id 
    FROM Post
    GROUP BY category_id
  ) AS filter
  ON source.id = filter.id;

If I understand correctly, the first step is to use a HibernateCriteriaBuilder:

def c = Post.createCriteria();
  def results = c.list {
    projections {
      groupProperty("category_id", "myid")
      max("id", "version")
    }
  }

So my question is a two part:

1. Am I on the right track?

2. How can I use the results object to obtain a List<Post> array?

   (Something like: def latest = Post.FindAllByXXX(result); )

Answer 1

Yes, you are on the right track. I would also add the id property for the Post to my projections:

projections {
    property('id')
}

and then collect all Posts using the id to get a list of posts, something like:

def latestPosts = results?.collect{Post.read(it[0])}