Rails：如果表單返回驗證錯誤，則保持 JSON 表單字段的填充

Question

我有一個創建產品的 rails 簡單表單，我在表單中有以下三個字段，以便將產品與適當的類別相關聯：

 <div class="form-group">
   <%= f.input :child_category_id, :collection => @categories.order(:name), :label_method => :name, :value_method => :id, label: "Category", :include_blank => "--Select Category--", input_html: { id: "first_dropdown" } %>
 </div>

 <div class="show_hide">
   <%= f.input :subcategory_id, :collection => [] || @subcategory.order(:name), :label_method => :name, :value_method => :id, label: false, :include_blank => "--Select Category--", input_html: { id: "second_dropdown" } %>
 </div>

 <div class="show_hide_third">
   <%= f.input :child_subcategory_id, :collection => [] || @child_subcategory.order(:name), :label_method => :name, :value_method => :id, label: false, input_html: { id: "third_dropdown" } %>
 </div>

這是路線：

resources :products, :path => "products/select_item", only: [:select_item] do
  get :select_item, on: :collection
end

這是我擁有的控制器內部的方法：

def select_item
  if params[:child_category_id].present?
    @subcategory = Subcategory.where(child_category_id: params[:child_category_id])
    render :json => @subcategory.order(:name)
  end
  if params[:subcategory_id].present?
    @child_subcategory = ChildSubcategory.where(subcategory_id: params[:subcategory_id])
    render :json => @child_subcategory.order(:name)
    end
end

這是我在控制器中的新產品和創建產品方法：

def new; end

def create
  @product = Product.new(product_params)
    respond_to do |format|
      if @product.save
        format.html { redirect_to root_path }
        format.json { render :new, status: :created, location: @product }
        flash[:success] = "Product was successfully added."
      else
        format.html { render :new }
        format.json { render json: @product.errors, status: :unprocessable_entity }
      end
    end
end 

這是我用來根據所選值填充第二個和第三個字段的 Javascript：

    $('#first_dropdown').on('change', function() {
        $.ajax({
            url: '/products/select_item/select_item?child_category_id=' + $(this).val(),
            dataType: 'json',
            success: function(data) {
                let childElement = $('#second_dropdown');
                if( data.length === 0 ) {
                    $('.show_hide').hide();
                    $('.show_hide_third').hide();
                } else {
                    $('.show_hide').show();
                }
                childElement.html('');
                data.forEach(function(v) {
                    let id = v.id;
                    let name = v.name;
                    childElement.append('<option value="' + id + '">' + name + '</option>');
                });
            }
        });
    });

    $('#second_dropdown').on('change', function() {
        $.ajax({
            url: '/products/select_item/select_item?subcategory_id=' + $(this).val(),
            dataType: 'json',
            success: function(data) {
                let childElement = $('#third_dropdown');
                if( data.length === 0 ) {
                    $('.show_hide').hide();
                    $('.show_hide_third').hide();
                } else {
                    $('.show_hide').show();
                    $('.show_hide_third').show();
                }
                childElement.html('');
                data.forEach(function(v) {
                    let id = v.id;
                    let name = v.name;
                    childElement.append('<option value="' + id + '">' + name + '</option>');
                });
            }
        });
    });

一切正常，所有字段都正確填充。 我遇到的唯一問題是，當表單再次呈現時，由於驗證錯誤，JSON 字段顯示為空，即使它們已正確填充。 即使表單返回驗證錯誤，我如何保持 JSON 表單字段填充？

Answer 1

問題是在頁面加載時，下拉列表中沒有選項可供選擇； 因此表單無法選擇正確的值。 你需要像這樣更新你的控制器：

def create
  @product = Product.new(product_params)
    respond_to do |format|
      if @product.save
        format.html { redirect_to root_path }
        format.json { render :new, status: :created, location: @product }
        flash[:success] = "Product was successfully added."
      else
        @categories = Category.all.order(:name)
        @subcategory = Subcategory.where(child_category_id: @product.child_category_id).order(:name)
        @child_subcategory = ChildSubcategory.where(subcategory_id: @product.subcategory_id).order(:name)
        format.html { render :new }
        format.json { render json: @product.errors, status: :unprocessable_entity }
      end
    end
end