SQL查询顺序问题
所以我在activerecord中有以下模型，我将使用Discussion.user_replied_group_discussions(@user)它返回最近回复的讨论好，但是如何修改私有方法以按最新回复时间订购返回的讨论？
# Table name: discussions # # id :integer not null, primary key # title :string(255) not null # content :text(255) not null # created_at :datetime # updated_at :datetime # user_id :integer # discussable_id :integer # discussable_type :string(255) class Discussion :commentable, :dependent => :destroy # #this is the scope that I am having trouble with: # scope :user_replied_group_discussions, lambda {|user| replied_by(user) } private def self.replied_by(user) discussion_ids = %(SELECT commentable_id FROM comments WHERE commentable_type = 'Discussion' AND user_id = :user_id) where("discussable_type = 'Group' AND id IN (#{discussion_ids}) ", { :user_id => user }) end end # Table name: comments # # id :integer not null, primary key # content :text # created_at :datetime # updated_at :datetime # commentable_id :integer # commentable_type :string(255) # user_id :integer # class Comment true belongs_to :user end
更新： @ypercube提供的sql查询帮助，我现在使用它与find_by_sql。 但是把它放在控制器中似乎很尴尬。
有更好的解决方案吗？ 谢谢！
这将根据最新的discussions.updated_at订购discussions.updated_at时间：
where("discussable_type = 'Group' AND id IN (#{discussion_ids}) order by updated_at DESC ",
如果您想通过comment.created_at订购，请使用以下查询：
SELECT d.* , MAX(c.created_at) AS lastCommentTime FROM discussions d JOIN comments c ON d.id = c.commentable_id WHERE c.commentable_type = 'Discussion' AND c.user_id = userIDtoCheck GROUP BY d.id ORDER BY lastCommentTime DESC <--- latest first