Rails：在嵌套模型表单中使用 Accepts_nested_attributes_for答案

【问题标题】：Rails: Using accepts_nested_attributes_for in Nested Model FormRails：在嵌套模型表单中使用 Accepts_nested_attributes_for
【发布时间】：2011-10-07 07:33:47
【问题描述】：

在我的应用中，用户有很多对话，对话有很多消息。我想创建一个新的对话：我必须指定用户（读者）和（第一条）消息。我尝试了以下方法，但失败了。

型号

class Conversation < ActiveRecord::Base

  has_many :conversation_users
  has_many :users, :through => :conversation_users

  has_many :messages

  accepts_nested_attributes_for :users
  accepts_nested_attributes_for :messages

end

class Message < ActiveRecord::Base

  belongs_to :conversation
  belongs_to :user

end

class User < ActiveRecord::Base

  has_many :conversation_users
  has_many :conversations, :through => :conversation_users

end

控制器

def new
  @conversation = Conversation.new
  2.times do
    users = @conversation.users.build
  end
  messages = @conversation.messages.build
end

def create
  @conversation = Conversation.new(params[:conversation])

  if @conversation.save
    redirect_to username_conversations_path(current_username)
  else
    redirect_to new_username_conversation_path(current_username)
  end
end

查看

<% form_for([current_user, @conversation]) do |f| %>

   <% f.fields_for :users do |builder| %>

     <%= builder.text_field :id %>

   <% end %>

   <% f.fields_for :messages do |builder| %>

     <%= builder.text_area :content %>

   <% end %>

   <%= f.submit "Submit" %>

<% end %>

current_user 和 current_username 是 helper 方法，定义如下：

def current_user
  @current_user ||= User.find(session[:user_id]) if session[:user_id]
end

def current_username
  @current_username ||= current_user.username if current_user
end

这是 Rails 服务器的响应：

Started POST "/users/8/conversations" for 127.0.0.1 at Sun Jul 17 23:58:27 +0200 2011
  Processing by ConversationsController#create as HTML
  Parameters: {"commit"=>"Submit", "authenticity_token"=>"z6kL+NmVspgCKMr9whcw+a85mA59j3jssS9QeTiEbxc=", "utf8"=>"✓", "conversation"=>{"users_attributes"=>{"0"=>{"id"=>"9"}, "1"=>{"id"=>"10"}}, "messages_attributes"=>{"0"=>{"content"=>"freee"}}}, "user_id"=>"8"}
  User Load (0.3ms)  SELECT "users".* FROM "users" INNER JOIN "conversation_users" ON "users".id = "conversation_users".user_id WHERE "users"."id" IN (9, 10) AND (("conversation_users".conversation_id = NULL))

ActiveRecord::RecordNotFound (Couldn't find User with ID=9 for Conversation with ID=):
  app/controllers/conversations_controller.rb:26:in `new'
  app/controllers/conversations_controller.rb:26:in `create'

conversations_controller 第 26 行：@conversation = Conversation.new(params[:conversation])

我怎样才能让它工作？

谢谢。

【问题讨论】：

“失败”是什么意思？有什么错误吗？
我添加了错误响应...这是一个找不到记录的错误
我在您的回复中看不到任何错误
什么是current_username？显示此帮助代码
current_username 是当前登录用户的用户名。 current_user 返回当前登录的用户（在这两种情况下，都是正在创建新对话的用户）

标签： ruby-on-rails has-many-through nested-attributes

【解决方案1】：

class Conversation < ActiveRecord::Base
  has_many :conversation_users
  has_many :users, :through => :conversation_users
  has_many :messages
  # NEXT LINE IS CHANGED!
  accepts_nested_attributes_for :conversation_users
  accepts_nested_attributes_for :messages
end

控制器

def new
  @conversation = Conversation.new
  2.times{ users = @conversation.conversation_users.build }
  messages = @conversation.messages.build
end

和形式

<%= form_for([current_user, @conversation]) do |f| %>
  <%= f.fields_for :conversation_users do |builder| %>    
    <%= builder.text_field :user_id %>
    <%= builder.hidden_field :conversation_id %>
  <% end %>
  ...
<% end %>

就是这样。

【讨论】：

对，我正在创建一个新的“conversation_user”对象，而不是“用户”对象！太好了 :) 感谢您的帮助

【解决方案2】：

<% form_for([current_user, @conversation]) do |f| %>

应该是

<%= form_for([current_user, @conversation]) do |f| %>

和

<% f.fields_for :messages do |builder| %>
# and
<% f.fields_for :users do |builder| %>

应该是

<%= f.fields_for :messages do |builder| %>
# and
<%= f.fields_for :users do |builder| %>

【讨论】：

@apneadiving 其实反之亦然:)

【解决方案3】：

替换：

   <% f.fields_for :users do |builder| %>

与：

   <%= f.fields_for :users do |builder| %>

同样缺少 '=' 有点低。

【讨论】：