How to join a table and count records in Rails 3?

ruby ruby-on-rails-3 arel
Yuval Karmi picture Yuval Karmi · Aug 10, 2011 · Viewed 8.6k times · Source

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?

Thanks!

Answer

Yuval Karmi picture Yuval Karmi · Aug 14, 2011

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.

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