RubyTutorial.org: Invalid SQL statement generates 500 response on pages#home

While the view contains(what I believe) is the correct UNLESS statement to display a feed, the SQL method from micropost.rb model seems to be invalid when a user is not following anyone. This error is transparent in a deployment environment(such as Heroku) -- here is the log snippet which generates a 500 response from the application:

Started GET "/" for 71.180.163.2 at Mon Jan 31 12:10:07 -0800开发者_StackOverflow 2011
  Processing by PagesController#home as HTML
Completed   in 9ms


ActiveRecord::StatementInvalid (PGError: ERROR:  syntax error at or near ")"
LINE 1: ...* FROM       "microposts"  WHERE     (user_id IN () OR user_...
                                                            ^

: SELECT     "microposts".* FROM       "microposts"  WHERE     (user_id IN () OR user_id = 1) ORDER BY  microposts.created_at DESC LIMIT 30 OFFSET 0):

app/controllers/pages_controller.rb:6:in `home'

The question is, how do I solve this issue without a hack-fix such as automatically following a user on User.create!

It it helps at all, the gist for this issue is here: https://gist.github.com/804754

Removing the initial self.from_users_followed_by method in the micropost model, leaving the private self.followed_by(user) method to stand alone, seems to have resolved the issue. All tests passing.

From models/micropost.rb

class Micropost < ActiveRecord::Base
attr_accessible :content

belongs_to :user

validates :content, :presence => true, :length => { :maximum => 140 }
validates :user_id, :presence => true

default_scope :order => 'microposts.created_at DESC'

#Return microposts from the users being followed by the given user--
scope :from_users_followed_by, lambda { |user| followed_by(user) }
# 
# def self.from_users_followed_by(user)
#   followed_ids = user.following.map(&:id).join(", ")
#   where("user_id IN (#{followed_ids}) OR user_id = ?", user)
# end

private

#Return an SQL condition for users followed by the given user.
#We include the user's own ID as well--
def self.followed_by(user)
  followed_ids = %(SELECT followed_id FROM relationships
                   WHERE follower_id = :user_id)
  where("user_id IN (#{followed_ids}) OR user_id = :user_id",
        :user_id => user)
end
end

It is never necessary to build a query string by hand like you are doing in your from_users_followed_by method. I would do something like:

def self.from_users_followed_by(user)
  followed_ids = user.following.map(&:id) + user.id
  where(:user_id => followed_ids)
end