在Rails 5 中从另一个模型中选择belongs_to 模型的有效方法？

Question

I have 2 models:

Contact -> has_many :messages 

and

Message -> belongs_to :contact

I want to select the last 10 contacts (as array of object, not only ids) from my messages table

this is my attempt (and it works fine):

Contact.where(id: Message.pluck(:contact_id).uniq.last(10))

BUt is there another better or rails way to do this?

EDIT I want to select the last 10 contacts from my messages table

Answer 1

I would do this in one database query.

Contact
  .distinct
  .joins(:messages)
  .order('messages.created_at DESC')
  .limit(10)

Answer 2

You could try the following query:

Contact.where(id: Message.distinct.order(created_at: :desc).limit(10).select(:id))

This would produce the following SQL:

"SELECT  DISTINCT \"messages\".\"id\" FROM \"messages\"   ORDER BY \"messages\".\"created_at\" DESC LIMIT 10"