Sort by association count in Grails

Question

I have many Topic objects and each Topic hasMany posts:Post How can I order all Topic objects based on their posts count??

Answer 1

You can do it in one HQL query with size() function. This way you get Topic instances in one query:

SELECT topic
FROM Topic topic
ORDER BY size(topic.posts)

I've found this on http://docs.jboss.org/hibernate/core/3.3/reference/en/html/queryhql.html, section 14.16 Tips & Tricks.