Rails 3中，HAS_ONE /的has_many與拉姆達條件

Question

這裏我的模型：

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 

我想獲取所有topics用，爲current_user，相關bookmark。 ATM，我這樣做：

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

這是醜陋的，做太多的數據庫查詢。我想這樣的事情：

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 

這可能嗎？我有其他選擇嗎？

謝謝！

Answer 1

*嗯，我不知道我理解你的問題，但是這可能會幫助您：

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

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

正如你可以看到範圍的參數for_user可以是用戶對象或用戶ID。

希望這會有所幫助！

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