form_for collection_select编辑时未显示已保存的选择

问：

我有一个用于新建和编辑的表单。该表格填写了产品名称、描述等。

此外，用户可以从嵌套下拉列表 （） 中选择一个项目，也可以创建一个新项目。在“新建”上，表单工作正常 - 所有条目和选择都保存。collection_select

当用户去编辑保存的产品时，表单会预加载该项目的所有已填写条目，但不会在collection_select内预加载其原始选择。

而且，如果用户想要编辑项目并决定创建一个新项目而不是之前选择的collection_select项目，则会出现一个错误，指出产品已使用该化学组创建。 对这种双重困境的任何帮助将不胜感激。我是 RoR 的新手，我确定我在某个地方遗漏了一些东西。

这是我的表格

<%= render partial: 'layouts/errors', locals: {object: @product} %>

<%= form_for(@product) do |f| %>
    <div>
        <%= f.label :name %><br>
        <%= f.text_field :name %><br>
    <div>
    <div>
        <%= f.label :active_ingredient %><br>
        <%= f.text_field :active_ingredient %><br>
    <div>
    <div>
        <%= f.label :description %><br>
        <%= f.text_area :description %><br>
    </div>
    <div>
        <%= f.label :image %><br>
        <%= f.file_field :image %><br>
    </div>
    <div>
        <p>Select a Chemical Group:</p>
        <%= f.collection_select :chem_group_id, ChemGroup.all, :id, :name, include_blank: 'Select One', selected: @product.chem_group, value: @product.chem_group.name %>
    </div>
    <div>
        <p>Or, create a new Chemical Group:</p>
        <!-- NESTED FORM! User writing attributes for another object. Use fields_for -->
        <%= f.fields_for :chem_group do |cg| %>
            <%= cg.label :name %>
            <%= cg.text_field :name %>
        <% end %>
    </div>
    <div>
        <p>Select an Application Area:</p>
        <%= f.collection_select :application_area_id, ApplicationArea.all, :id, :area_name, include_blank: 'Select One', selected: @product.application_area, value: @product.application_area.area_name %>
    </div>
    <div>
        <p>Or, create a new Application Area:</p>
        <!-- NESTED FORM! User writing attributes for another object. Use fields_for -->
        <%= f.fields_for :application_area do |aa| %>
            <%= aa.label :area_name %>
            <%=aa.text_field :area_name %>
        <% end %>
    </div>
    <br>
    <%= f.submit "Save" %>
<% end %>

这是我的模型

class Product < ApplicationRecord
  belongs_to :chem_group
  belongs_to :application_area
  belongs_to :user #admin creator
  accepts_nested_attributes_for :chem_group #tells the model to accept chem_group attributes from cg nested form in new product form
  accepts_nested_attributes_for :application_area

  validates :active_ingredient, presence: true
  validates :application_area, presence: true
  validates :description, presence: true
  validates :name, presence: true
  validate :not_a_duplicate #checking for what we DON'T WANT

  def chem_group_attributes=(attributes)
    self.chem_group = ChemGroup.find_or_create_by(attributes) if !attributes['name'].empty?
    self.chem_group
  end

  def application_area_attributes=(attributes)
    self.application_area = ApplicationArea.find_or_create_by(attributes) if !attributes['area_name'].empty?
    self.application_area
  end

  #if there is already a product with that name && chem_group, give error
  def not_a_duplicate
    #calling the instance of the attribute [string/integer: key]
      if Product.find_by(name: name, chem_group_id: chem_group_id)
        errors.add(:name, 'has already been created for that Chemical Group')
      end
    end
end

这是我的控制器

class ProductsController < ApplicationController

    def new
        if logged_in?
            @product = Product.new
            1.times {@product.build_chem_group} #for the nested form. Builds the chem_group attributes
            @product.build_application_area
        else
            flash[:error] = "Sorry, you must be logged in to create a new product."
            redirect_to products_path
        end
    end

    def create
        @product = Product.new(product_params)
        @product.user_id = session[:user_id] #bc product belongs_to user. user_id required from model
        if @product.save #validation
            # @product.image.purge
            # @product.image.attach(params[:product][:image]) # allows image to be replaced if user changes image
            redirect_to product_path(@product)
        else
            @product.build_chem_group
            @product.build_application_area
            render :new
        end
    end

    def edit
        find_product
        1.times {@product.build_chem_group}
        if @product.user != current_user
            flash[:error] = "Sorry, you can only edit your own products"
            redirect_to products_path
        end
    end

    def update
        find_product
        if @product.update(product_params)
            redirect_to product_path(@product)
        else
            render :edit
        end
    end

    private

    def product_params
        params.require(:product).permit(:name, :description, :active_ingredient, :image, :chem_group_id, :application_area_id, chem_group_attributes: [:id, :name], application_area_attributes: [:id, :area_name])
        #chem_group_id and chem_group_attributes [:name] is permitting elements from new product form
    end

    def find_product
        @product = Product.find_by(id: params[:id])
    end

end