Association function in Rails

I have Users, Hosts, and Checkins.

Users -> has_many -> Hosts -> has_many -> Checkins

Checkin -> belongs_to 开发者_开发知识库-> Host -> belongs_to -> User

How can I easily do a query for all checkins for a particular user without writing my own SQL?

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Use a has_many :through association, like this:

has_many :checkins, :through => :hosts

You can then simply use checkins as your direct association. Whoo hoo!