Ruby rails 3 Nested Form无法保存，因为before_save方法访问对象为nil的父模型

Question

我的rails应用程序中有一个嵌套的窗体/模型，除了before_save方法在使用嵌套窗体时无法访问父@user对象外，它可以正常工作。不过，在保存子模型本身时，它可以很好地工作。。

这是简化代码

class Forum < ActiveRecord::Base
  has_many :forum_post, :dependent => :destroy
  belongs_to :project
  accepts_nested_attributes_for :forum_post,  :reject_if => :all_blank
end
class ForumPost < ActiveRecord::Base
    belongs_to :forum    
    belongs_to :user
    before_save :toggle_forum              
    has_attached_file :attachment
 def toggle_forum   
    #a bunch of code
    #one line tries to access @user.id but it fails because @user is nil
    @user.id

  end
 end

然后在我的ForumControler控制器中，它更新了这一点，我有

def update
 @forum = Forum.find(params[:id])    
 if @forum.update_attributes(params[:forum])               
     redirect_to(user_forum_path(@user,@forum.project,@forum), :notice => 'Forum was successfully updated.')
  else        
     render :action => 'submit'        
  end

结束

在我看来：

<%= form_for(@forum, :url => user_forum_path, :html => { :multipart => true, :id => :project } ) do |f| %>    
    <div class="form-label-row summary-text">
      <%= f.label(:summary_text, 'Final Summary') %>
      <%= f.text_area :summary_text %>
    </div>
    <%= f.fields_for :forum_post,$forum_post do |child_form| %>
        <div class="form-row-left attachment">
            <%= child_form.label :attachment %>
            <%= child_form.file_field :attachment %>    
        </div>
        <!-- I tried adding with and without the next 2 hidden fields and it failed either way -->
        <%= child_form.hidden_field :user_id, :value=>@user.id %>               
        <%= child_form.hidden_field :forum_id, :value=>@forum.id %>
    <% end %>
    <%= hidden_field(:forum, :state, :value => :student_completed) %>
    <div class="form-buttons" id="submit">
        <%= f.submit "Submit Project" %>
    </div>
<% end %>

问题是，如果@user在将forum_post保存为嵌套对象时为nil。。如果我将forum_post保存在它自己的模型中，它就可以正常工作。知道为什么从父对象保存时没有填充@user变量吗？

Answer 1

您确定要使用实例变量而不是关联吗？尝试：

 def toggle_forum   
   #a bunch of code
   #one line tries to access @user.id but it fails because @user is nil
   user.id
 end