I have a Collection
class which has many coins.
I am trying to select collections which have more than two coins.
Currently, I have no problem doing that through straight Ruby, but that's extremely inefficient.
My current code:
collections = Collection.all.select { |c| c.coins.count > 2 }
How do I achieve that through a joins
call with Arel?开发者_JAVA技巧
Thanks!
To answer my own question:
Collection.joins(:coins).group("coins.collection_id").having("count(coins.id) > 2")
Hat tip to KJF who asked this similar question and to krakover for answering it.
Add counter_cache columns and query them.
http://railscasts.com/episodes/23-counter-cache-column
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