form_for with has_many：通過

Question

所以我有一個簡單的post模型has_many標籤：通過post_tags。這允許多對多的關係。不過，我一直無法獲得form_for和fields_for的工作。我真的被卡住了，因爲我無法通過has_many：through關係在form_for helper上找到任何文檔。我觀察了軌道投影，閱讀了以前的堆棧問題，甚至在Rails 3 Way中進行了研究。任何人，這是我得到的。

class Post < ActiveRecord::Base 
    belongs_to :blog 

    has_many :post_tags, :dependent => :destroy 
    has_many :tag, :through => :post_tags, :dependent => :destroy 

    has_many :post_categories, :dependent => :destroy 
    has_many :category, :through => :post_categories, :dependent => :destroy 

    attr_accessible(:title, ...) 

    accepts_nested_attributes_for :tag, :allow_destroy => true 

end 

和

class PostTag < ActiveRecord::Base 
    belongs_to :tag 
    belongs_to :post 
end 

和

class Tag < ActiveRecord::Base 
    has_many :post_tags 
    has_many :post, :through => :post_tags 
end 

和我的控制器代碼是

def new 
    @title = "Create a New Post" 
    @user = User.find(params[:user_id]) 
    @blog = @user.blog 
    @post = @blog.post.new 
    @post.ptype = params[:type] 
    3.times { @post.tag.build} 
    end 

    def create 
    @user = User.find(params[:user_id]) 
    @blog = @user.blog 
    @post = @blog.post.new(params[:post]) 

    if @post.save 
     ... 
    end 
    end 

和形式是

<%= form_for([@user,@blog,@post],:url => user_blogs_posts_path, :html => {:multipart=>true}) do |p| %> 
    <%= render 'shared/error_messages', :object => p.object %> 
    ... 
     <%= p.fields_for :tag do |t|%> 
      <%=t.label :tag %> 
      <%=t.text_field :tag %> 
     <% end %> 

     <%=p.submit%> 
<% end %> 

，誤差

Can't mass-assign protected attributes: tag_attributes 

Answer 1

添加:tag_attributes到attr_accessible在Post

attr_accessible :title, ..., :tag_attributes, ...