ruby-on-rails - Rails 4.2 Nested Forms--SQL在加载 'Edit'页面时自动删除嵌套表单内容

Question

我用这个Blog作为在 Ruby on Rails 4.2 上学习嵌套表单 的指南。我尝试使用此指令中的相同步骤在 Post 模型中创建位置嵌套表单。

使用嵌套位置表单创建新的post 后，位置内容正确显示在post 的 显示页面上。但是，当我打开 edit 页面时，位置内容都没有了。仔细查看日志，发现如下信息:

Started GET "/categories/category#name/posts/323/edit"...
Location Load (0.1ms)  SELECT  "locations".* FROM "locations" WHERE "locations"."post_id" = ? LIMIT 1  [["post_id", 323]]
   (0.1ms)  begin transaction
  SQL (0.4ms)  DELETE FROM "locations" WHERE "locations"."id" = ?  [["id", 27]]

似乎嵌套形式创建的内容在加载编辑页面时被 SQL 自动删除。

这是我的代码:

   class Post < ActiveRecord::Base
      belongs_to :user
      belongs_to :category

      has_one :location, dependent: :destroy

      accepts_nested_attributes_for :location, reject_if: lambda { |a| a['street'].blank? },
                                     allow_destroy: true
      def to_s
        title
      end
   end

位置模型:

class Location < ActiveRecord::Base
  belongs_to :post
  has_one :user, through: :post


  validates :city, presence: true
  validates :zipcode, presence: true,
             format: { with: /\A\d{5}\z/i }


end

帖子 Controller :

 class Categories::PostsController < ApplicationController
    ...
    def new
        @category = Category.friendly.find(params[:category_id])
        @post = Post.new
        @post.build_location
      end

      def create
        @category = Category.friendly.find(params[:category_id])
        @post = current_user.posts.build(post_params)
        @post.category = @category

        if @post.save
          flash[:success] = "You have succesfully created a new post."
          redirect_to [@category, @post]
        else
          flash[:error] = "Error occured. Please try again."
          render :new
        end
      end

      def edit
        @category = Category.friendly.find(params[:category_id])
        @post = Post.find(params[:id])
        @post.build_location
      end

      def update
        @category = Category.friendly.find(params[:category_id])
        @post = Post.find(params[:id])
          if @post.update_attributes(post_params)
            flash[:success] = "Post was upated."
            redirect_to [@category, @post]
          else
            flash[:error] = "There was an error saving a post, please try again."
            render :new
          end
      end
    ...
    private 

        def post_params
          params.require(:post).permit(:title, :body, location_attributes: [:id, :street, :city, :zipcode, :_destroy])
        end

app/views/posts/_form.html.erb

<%= form_for [@category, @post] do |f| %>
  ...
  <strong>Location:</strong>
  <div class="well">
    <%= f.fields_for :location do |location| %>
      <%= location.label :street %>
  <%= location.text_field :street, placeholder: "If you don't want to provide your address, just put 'NA' in this field" %>

  <%= location.label :city %>
  <%= location.text_field :city %>

  <%= location.label :zipcode%>
  <%= location.text_field :zipcode %>

  <%= location.check_box :_destroy %>
  <%= location.label :_destroy, 'remove' %>
    <% end %>
  </div>

虽然按照我所遵循的说明一切正常，但当我在服务器上测试我的应用程序时，我不断收到“静默”错误。如何使嵌套表单中的现有数据显示在编辑页面上？

欢迎任何见解，并提前致谢!

Answer 1

更新 Controller 中的编辑方法。仅在帖子没有关联位置时构建实例。

@post.build_location if @post.location.blank?