在Rails中更新嵌套的fields_for和collection_select(Updating nested fields_for and collection_select in Rails)

 真的难倒在这里。 我正在尝试让我的表单更新edit表单上的类别。 问题是，除了类别之外，我提交的表格中的所有内容都会更新。 它最终会插入所选择的新类别，就像它通过create方法而不是update方法一样，所以当提交后再次显示编辑表单时，它会使类别的字段加倍。 每次提交后1，然后是2，然后是4，然后是8等。 请帮助任何人。 欣赏它。 
 
 视图/ blog_posts / edit.html.erb 
 
<div class="col-md-6 col-md-offset-3 blog-submit">
            <%= form_for @blog_post do |b| %>


             <%= b.label :title %>
             <%= b.text_field :title %><br>

                <%= b.fields_for :categorizations do |cat| %>
                <%= cat.label :category_name, "Category 1" %>
                <%= cat.collection_select(:category_id, Category.all, :id, :category_name, {blank: "Select Category"}) %>
                <%= link_to "Add Categories", new_category_path %>
                  <br>
                <% end %>

                <%= b.submit "Submit", class: "btn btn-primary" %>
          <% end %>
        </div>
 
 Blog_post控制器： 
 
class BlogPostsController < ApplicationController
    protect_from_forgery
    before_action :authenticate_admin!, only: [:new, :edit]

    def index
      @blog_posts = BlogPost.order(id: :desc)
    end

    def new
      @blog_post = BlogPost.new
      @blog_post.categorizations.build.build_category
      @blog_post.categories.build
    end

    def edit
         @blog_post = BlogPost.find(params[:id])
    end

    def create
      @blog_post = BlogPost.new(blog_post_params)
      respond_to do |format|
          if @blog_post.save
            format.html { redirect_to @blog_post, notice: 'Your blog was submitted successfully' }
            format.json { render :show, status: :created, location: @blog_post }
          else
            format.html { render :new }
            format.json { render json: @blog_post.errors, status: :unprocessable_entity }
          end
        end
        puts @blog_post.errors.inspect
    end

    def update
        @blog_post = BlogPost.find(params[:id])
        if @blog_post.update_attributes(blog_post_params)
          render 'show'  
        else
          render 'edit'
        end
    end

    def show
        @blog_post = BlogPost.find(params[:id])

    end



private

  def blog_post_params
    params.require(:blog_post).permit(:title, :content, :posted_by, :comments, :blog_pic, {categorizations_attributes: [:category_id, :category_name]})
  end

end
 
 楷模： 
 
class BlogPost < ApplicationRecord
    has_many :categorizations
    has_many :categories, :through => :categorizations
    accepts_nested_attributes_for :categorizations
    has_many :comments
    mount_uploader :blog_pic, BlogPicUploader
end

class Categorization < ApplicationRecord
    belongs_to :blog_post
    belongs_to :category
end

class Category < ApplicationRecord
    has_many :categorizations
    has_many :blog_posts, :through => :categorizations 
end

Really stumped here. I'm trying to get my form to update the categories on the edit form. Problem is, everything in my form updates when submitted except the categories. It ends up inserting the new category chosen like it's going through the create method instead of the update method, so when the edit form is shown again after submission, it keeps doubling the fields of categories. 1, then 2, then 4, then 8, etc. after each submission. Please please help anyone. Appreciate it. 
 
views/blog_posts/edit.html.erb
 
<div class="col-md-6 col-md-offset-3 blog-submit">
            <%= form_for @blog_post do |b| %>


             <%= b.label :title %>
             <%= b.text_field :title %><br>

                <%= b.fields_for :categorizations do |cat| %>
                <%= cat.label :category_name, "Category 1" %>
                <%= cat.collection_select(:category_id, Category.all, :id, :category_name, {blank: "Select Category"}) %>
                <%= link_to "Add Categories", new_category_path %>
                  <br>
                <% end %>

                <%= b.submit "Submit", class: "btn btn-primary" %>
          <% end %>
        </div>
 
Blog_post controller: 
 
class BlogPostsController < ApplicationController
    protect_from_forgery
    before_action :authenticate_admin!, only: [:new, :edit]

    def index
      @blog_posts = BlogPost.order(id: :desc)
    end

    def new
      @blog_post = BlogPost.new
      @blog_post.categorizations.build.build_category
      @blog_post.categories.build
    end

    def edit
         @blog_post = BlogPost.find(params[:id])
    end

    def create
      @blog_post = BlogPost.new(blog_post_params)
      respond_to do |format|
          if @blog_post.save
            format.html { redirect_to @blog_post, notice: 'Your blog was submitted successfully' }
            format.json { render :show, status: :created, location: @blog_post }
          else
            format.html { render :new }
            format.json { render json: @blog_post.errors, status: :unprocessable_entity }
          end
        end
        puts @blog_post.errors.inspect
    end

    def update
        @blog_post = BlogPost.find(params[:id])
        if @blog_post.update_attributes(blog_post_params)
          render 'show'  
        else
          render 'edit'
        end
    end

    def show
        @blog_post = BlogPost.find(params[:id])

    end



private

  def blog_post_params
    params.require(:blog_post).permit(:title, :content, :posted_by, :comments, :blog_pic, {categorizations_attributes: [:category_id, :category_name]})
  end

end
 
models:
 
class BlogPost < ApplicationRecord
    has_many :categorizations
    has_many :categories, :through => :categorizations
    accepts_nested_attributes_for :categorizations
    has_many :comments
    mount_uploader :blog_pic, BlogPicUploader
end

class Categorization < ApplicationRecord
    belongs_to :blog_post
    belongs_to :category
end

class Category < ApplicationRecord
    has_many :categorizations
    has_many :blog_posts, :through => :categorizations 
end

原文：