轨道3，HAS_ONE /的has_many与拉姆达条件 [英] Rails 3, has_one / has_many with lambda condition

问题描述

下面我的模型：

class User < ActiveRecord::Base
  has_many :bookmarks
end

class Topic < ActiveRecord::Base
  has_many :bookmarks
end

class Bookmark < ActiveRecord::Base
  belongs_to :user
  belongs_to :topic
  attr_accessible :position
  validates_uniqueness_of :user_id, :scope => :topic_id
end

我想获取所有主题用，为 CURRENT_USER ，相关的书签。自动取款机，我做的：

I want to fetch all topics with, for current_user, the associated bookmark. ATM, I do:

Topic.all.each do |t|
    bookmark = t.bookmarks.where(user_id: current_user.id).last
    puts bookmark.position if bookmark
    puts t.name
end

这是丑陋的，做了太多的数据库查询。我想是这样的：

This is ugly and do too much DB queries. I would like something like this:

class Topic < ActiveRecord::Base
  has_one :bookmark, :conditions => lambda {|u| "bookmarks.user_id = #{u.id}"}
end

Topic.includes(:bookmark, current_user).all.each do |t| # this must also includes topics without bookmark
    puts t.bookmark.position if t.bookmark
    puts t.name
end

这可能吗？我有没有任何别的选择吗？

Is this possible? Have I any alternative?

感谢您！

推荐答案

*嗯，我不知道我理解你的问题，但是这可能会帮助您：

*Hmm I'm not sure I understood your question but this may help you:

# code
class Topic < ActiveRecord::Base
  scope :for_user, lambda do |user| 
    includes(:bookmarks).where(bookmarks: { user_id: user.try(:id) || user} ) 
  end

# call
Topic.for_user(current_user) # => Array of Topics

正如你所看到的参数范围 for_user 可以是用户对象或用户ID 。

希望这有助于！

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