Rails - Oct 2010 - Struggling with a complex Rails 3 query (user.friends.checkins)

I''m working on a social networking application and am trying to build
a complex query that efficiently pulls all of a users''
friends''
checkins from the database.  Basically I need: "user.friends.checkins"

I''ve recreated (in simplified form) the data structure below for
reference and included several solutions I''ve found, however I feel
like my solutions are sub-optimal.  I''m hoping that someone can point
out a better way...  So here goes:

# === My Solutions ==I tried this first, which works, but is way too slow given
that users
typically have +1000 friends each:
=> Checkin.where(:user_id => self.friends)

Then I tried this, which also works and is much faster, but feels
sloppy:
=> Checkin.joins(:user).joins(''INNER JOIN "friendships" ON
"users"."id" =
"friendships"."friend_id"'').where(:friendships
=>
{:user_id => 1})

Any help you can provide would be GREATLY appreciated!  Thanks in
advance!!!

# === Data structure ==# Users table columns: id, name
# Friendships table columns: user_id, friend_id
# Checkin table columns: id, location, user_id

# === Models ==class User
  has_many :friendships
  has_many :friends, :through => :friendships
  has_many :checkins
end

class Friendship
  belongs_to :user
  belongs_to :friend, :class_name => ''User''
end

class Checkin
  belongs_to :user
end

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