如何更新，或創建的/對象放入集合

Question

我有一個可以存儲答案和教訓列表的User類

has_many :answers 
    has_many :lessons, :through => :answers 

答案類：

class Answer < ActiveRecord::Base 
    belongs_to :user 
    belongs_to :lesson 

    attr_accessible :finished, :current_solution 
end 

每用戶上課的時間，我想存儲他的最新答案。我試圖做這樣的：

if current_user 
    @lesson = Lesson.find(params[:id]) 
    @code = request.request_parameters["code"] 
    @user = User.find(session[:user_id]) 
    begin  # retrieve an old answer, if possible 
    @answer = Answer.find [params[:id], session[:user_id]] 
    rescue 
    end 
    if not @answer # else create a new one 
    @answer = Answer.new 
    @answer.lesson_id = @lesson.id 
    @answer.user_id = @user.id 
    @user.answers << @answer # store it in the user's answers list 
    end 

    @validation_passed = @lesson.validate(@code) 
    @answer.finished = @validation_passed # update answer 
    @answer.current_solution = @code 

數據庫模式：

create_table "answers", :id => false, :force => true do |t| 
    t.integer "lesson_id",  :null => false 
    t.integer "user_id",   :null => false 
    t.string "finished" 
    t.string "current_solution" 
    end 

    add_index "answers", ["lesson_id", "user_id"], :name => "index_answers_on_lesson_id_and_user_id", :unique => true 

我得到一個異常columns lesson_id, user_id are not unique，或columns lesson_id, user_id are not unique: INSERT INTO "answers" ("current_solution", "finished", "lesson_id", "user_id") VALUES (?, ?, ?, ?)，但我不明白爲什麼這會發生，因爲我只能創建新的對象，如果沒有找到與相應的座標..

如果有人能告訴我我做錯了什麼，我會很高興。

在此先感謝！ :)

Answer 1

你的查詢找到PARAMS的Answer是不正確的 - 它應該是：

@answer = Answer.find_by_lesson_id_and_user_id(@lesson.id, @user.id) 

您也可以跳過begin - 這樣做時這樣end塊 - rescue。

如果你搜索的關聯，可以進一步簡化這個：

@answer = @user.answers.where(:lesson_id => @lesson).first 

此外，您可以將範圍添加到Answer類，如果這是一個常見的查詢：

class Answer < ActiveRecord::Base 
    scope :for_lesson, lambda{ |lesson| where(:lesson_id => lesson) } 
end 

而且那麼你可以簡化爲：

@answer = @user.answers.for_lesson(@lesson).first