rails3 scope for count of children in has_many relationship

Question

trying to do a scope in rails3.

:book has_many :chapters 

I want scope :long to return books with > 10 chapters.

How best to structure

Answer 1

Ah - to answer my own question in the comment above, I had to put the count in the HAVING:

class Book
  scope :long, joins(:chapters).
    select('books.id').
    group('books.id').
    having('count(chapters.id) > 10')
end