相关疑难解决方法(0)

是否可以在rails 3中的habtm关系上使用计数器缓存？

我真的需要它来加速我的应用程序.

我如何优化我的SQL查询,忽略这样的情况:

Meeting.find(5).users.size => SELECT COUNT(*)FROM ... WHERE ...

User.find(123).meetings.size => SELECT COUNT(*)FROm ... WHERE ...

我不知道如何在这里使用counter_cache.

这是我的模型关系:

class Meeting < ActiveRecord::Base
  has_many :meeting_users
  has_many :users, :through => meeting_users
end

class User < ActiveRecord::Base
  has_many :meeting_users
  has_many :meetings, :through => meeting_users
end

class Meeting_user < ActiveRecord::Base
  belongs_to :meeting
  belongs_to :user
end

什么是最优解决方案？

如何在这里实现counter_cache？

我有一个带有关联的Post和Tag模型many-to-many:

post.rb:

class Post < ActiveRecord::Base
  attr_accessible :title, :content, :tag_names

  has_many :taggings, :dependent => :destroy
  has_many :tags, :through => :taggings

  attr_writer :tag_names
  after_save :assign_tags

  def tag_names
    @tag_names || tags.map(&:name).join(" ")
  end

  private

  def assign_tags
    ntags = []
    @tag_names.to_s.split(" ").each do |name|
      ntags << Tag.find_or_create_by_name(name)
    end
    self.tags = ntags
  end
end

tag.rb:

class Tag < ActiveRecord::Base
  has_many :taggings, :dependent => :destroy  
  has_many :posts, :through => :taggings
  has_many :subscriptions
  has_many :subscribed_users, :source => :user, :through => …