Refactor Microposts so that I don't have ugly SQL

micropost.rb

class Micropost < ActiveRecord::Base
  attr_accessible :content
  belongs_to :user
  
  validates   :content,   :presence => true, :length => { :maximum => 140 }
  validates   :user_id,   :presence		 => true

  paginates_per 10
  
  default_scope :order => "microposts.created_at DESC"

  scope :from_users_followed_by, lambda{ |user| followed_by(user)}

  private 
    
    def self.followed_by(user)
        
      followed_ids  = %(SELECT followed_id FROM relationships WHERE follower_id = :user_id)

      # Confused here, but looking into Arel or some ActiveRecord non-sql solution
      # --------------------------------------------------------------------------------------------
      # followed_ids  = Relationship.select('relationships.followed_id').where(:follower_id => user)
      # m = Micropost.arel_table
      # where(m[:user_id].in(followed_ids).or(m[:user_id].eq(user)))

      # workaround for when followed_ids empty, ugly will refactor
      if followed_ids.present?
        where("user_id in (#{followed_ids}) OR user_id = :user_id", :user_id => user) 
      else 
        where("user_id = ?", user)
      end
    end

end