如何将find_by_sql语句转换为named_scope？

Question

如何将以下内容转换为named_scope？

  def self.commentors(cutoff=0)
    return User.find_by_sql("select users.*, count(*) as total_comments from users, comments 
      where (users.id = comments.user_id) and (comments.public_comment = 1) and (comments.aasm_state = 'posted') and (comments.talkboard_user_id is null) 
      group by users.id having total_comments > #{cutoff} order by total_comments desc")
  end

这就是我现在所拥有的，但它似乎不起作用：

  named_scope :commentors, lambda { |count=0|
    { :select => "users.*, count(*) as total_comments",
      :joins => :comments,
      :conditions => { :comments => { :public_comment => 1, :aasm_state => 'posted', :talkboard_user_id => nil} },
      :group => "users.id",
      :having => "total_comments > #{count.to_i}",
      :order => "total_comments desc"
    }
  }

最终，这就是起作用的；

  named_scope :commentors, lambda { |*args|
      { :select => 'users.*, count(*) as total_comments',
        :joins => :comments,
        :conditions => { :comments => { :public_comment => 1, :aasm_state => 'posted', :talkboard_user_id => nil} },
        :group => 'users.id',
        :having => ['total_comments > ?', args.first || 0],
        :order => 'total_comments desc' }
      }  

Answer 1

您遇到的问题是因为您用 comments 的内部联接替换了从 users, comments 中进行选择。要将 SQL 正确转换为 named_scope，请使用以下命令：

named_scope :commentors, lambda { |cutoff|
    { :select => 'users.*, count(*) as total_comments',
      :conditions => { :comments => { :public_comment => 1, :aasm_state => 'posted', :talkboard_user_id => nil } },
      :from => 'users, comments',
      :group => 'users.id',
      :having => ['total_comments > ?', cutoff],
      :order => 'total_comments desc' } }

并且 lambda 参数不能有默认值，因此不能使用 |cutoff = 0|。