RubyTutorial.org:无效的SQL语句在pageshome上生成500个响应

虽然视图包含了我认为正确的除非语句来显示提要，但是当用户没有跟踪任何人时，micropost.rb模型中的SQL方法似乎是无效的。此错误在部署环境（如Heroku）中是透明的-以下是从应用程序生成500响应的日志片段：

Started GET "/" for 71.180.163.2 at Mon Jan 31 12:10:07 -0800 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\u controller.rb:6:in'home'

问题是，我如何解决这个问题，没有黑客修复，如自动跟踪用户的user.create

---

这是有帮助的，这个问题的要点如下：

在micropost模型中删除最初的self.from_users_following_by method，而保留private self.following by user方法独立，似乎已经解决了这个问题。所有测试都通过了

来自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

---

不必像在from_users_后面跟着方法中那样手工构建查询字符串。我会这样做：

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

---

谢谢cam，事实上我意识到了这一点，但是Hartl要求我们使用手工构建的SQL查询-可能只是为了给初学者一些SQL的味道。这个过程的整个部分有点像意大利面条——不过谢谢你的代码建议@乔恩·保罗：有趣。在这种情况下，也许您仍然应该将user.id添加到后面的\u id数组中，并删除OR user\u id子句。至少这样您就不会有被传入的危险，我假设用户总是被定义的。编辑：刚刚意识到你已经解决了你的问题。对不起，没问题！谢谢你这么棒，卡姆+