Question

I am getting a 500 error when I try to deploy my app to Heroku (it works fine on my localhost). Not sure why this is happening.

How can I fix it? Error details are below…

Error Details

2012-01-03T10:33:49+00:00 app[web.1]: Started GET "/" for 

2012-01-03T10:33:49+00:00 app[web.1]:   Processing by PagesController#home as HTML
2012-01-03T10:33:49+00:00 app[web.1]: 
2012-01-03T10:33:49+00:00 app[web.1]: Completed   in 15ms
2012-01-03T10:33:49+00:00 app[web.1]: 
2012-01-03T10:33:49+00:00 app[web.1]:   app/controllers/pages_controller.rb:7:in `home'
2012-01-03T10:33:49+00:00 app[web.1]: ActiveRecord::StatementInvalid (PGError: ERROR:      syntax error at or near "["
2012-01-03T10:33:49+00:00 app[web.1]: : SELECT     "posts".* FROM       "posts"  WHERE        (user_id IN ([]) OR user_id = 2) ORDER BY  posts.created_at DESC LIMIT 30 OFFSET 0):
2012-01-03T10:33:49+00:00 app[web.1]: 
2012-01-03T10:33:49+00:00 app[web.1]: LINE 1: ...sts".* FROM       "posts"  WHERE       (user_id IN ([]) OR use...
2012-01-03T10:33:49+00:00 app[web.1]:             

Pages Controller

class PagesController < ApplicationController

def home
  @title = "Home"
  if signed_in?
      @post = Post.new
      @feed_items = current_user.feed.paginate(:page => params[:page])
  end
end

User Model

class User < ActiveRecord::Base

has_many :posts, :dependent => :destroy

has_many :relationships, :foreign_key => "follower_id",
:dependent => :destroy
has_many :reverse_relationships, :foreign_key => "followed_id",
:class_name => "Relationship",
:dependent => :destroy

has_many :following, :through => :relationships, :source => :followed
has_many :followers, :through => :reverse_relationships, :source => :follower

attr_accessor :password
attr_accessible :name, :email, :password, :password_confirmation

email_regex = /\A[\w+\-.]+@[a-z\d\-.]+\.[a-z]+\z/i

validates :name,     :presence => true,
                     :length => { :maximum => 50 }

validates :email,    :presence => true,
                     :format => { :with => email_regex },
                     :uniqueness => { :case_sensitive => false}

validates :password, :presence     => true,
                     :confirmation => true,
                     :length       => { :within => 6..40 }

before_save :encrypt_password

def has_password?(submitted_password)
    encrypted_password == encrypt(submitted_password)
end

def self.authenticate(email, submitted_password)
    user = find_by_email(email)
    return nil  if user.nil?
    return user if user.has_password?(submitted_password)
end

def self.authenticate_with_salt(id, cookie_salt)
    user = find_by_id(id)
    (user && user.salt == cookie_salt) ? user : nil
end

def following?(followed)
    relationships.find_by_followed_id(followed)
end

def follow!(followed)
    relationships.create!(:followed_id => followed.id)
end

def unfollow!(followed)
    relationships.find_by_followed_id(followed).destroy
end

def feed
    Post.from_users_followed_by(self)
end

private

def encrypt_password
    self.salt = make_salt unless has_password?(password)
    self.encrypted_password = encrypt(password)
end

def encrypt(string)
    secure_hash("#{salt}--#{string}")
end

def make_salt
    secure_hash("#{Time.now.utc}--#{password}")
end

def secure_hash(string)
    Digest::SHA2.hexdigest(string)
end

end

Post Model

class Post < ActiveRecord::Base
attr_accessible :content

belongs_to :user

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

default_scope :order => 'posts.created_at DESC'

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

def self.from_users_followed_by(user)
  following_ids = user.following_ids
  where("user_id IN (#{following_ids}) OR user_id = ?", user)
end

private

def self.followed_by(user)
  following_ids = %(SELECT followed_id FROM relationships
        WHERE follower_id = :user_id)
  where("user_id IN (#{following_ids}) OR user_id = :user_id",
       { :user_id => user })
end
end

Answer 1

Your problem is here:

def self.from_users_followed_by(user)
  following_ids = user.following_ids
  where("user_id IN (#{following_ids}) OR user_id = ?", user)
  #------------------^^^^^^^^^^^^^^^^
end

Your following_ids will be an array and when you "#{array}", you get things like [] and [11, 23, 42]. So that where will end up looking like this:

where("user_id IN ([]) OR user_id = ?", user)
where("user_id IN ([11, 23, 42]) OR user_id = ?", user)

neither of those contain valid SQL. Some databases might ignore the stray brackets but PostgreSQL will not.

You need to make two changes:

1. Don’t include the user_id IN (...) at all if following_ids is empty. Doing c in () isn’t valid SQL so you don’t want to do that. Again, some databases are lenient and forgiving, PostgreSQL is (thankfully) neither of those things.
2. Don’t use simple string interpolation to supply values for your IN; for that matter, don’t use string interpolation for your SQL at all (unless there is absolutely no other way and that’s rare): we’re not writing PHP in 1999, we’re supposed to know better now. Lucky for you (and the rest of us), AR will do the Right Thing if you hand it an array for a placeholder value.

Something like this should work better:

def self.from_users_followed_by(user)
  following_ids = user.following_ids
  if(following_ids.empty?)
    where('user_id = ?', user)
  else
    where('user_id in (?) or user_id = ?', following_ids, user)
  end
end

You could also do it like this:

def self.from_users_followed_by(user)
  following_ids = user.following_ids
  if(following_ids.empty?)
    where('user_id = ?', user)
  else
    following_ids.push(user.id)
    where('user_id in (?)', following_ids
  end
end

or, my favorite, like this:

def self.from_users_followed_by(user)
  where('user_id in (?)', user.following_ids + [user.id])
end