在Ruby on Rails 5中验证失败后重新呈现_form.html.erb时失败

Question

My application manages Business Rules, which apply to one business object. When editing a business rule, I meet an unattended failure.

The _form.html.erb view correctly displays current properties, including the dropdown field :

<%= f.collection_select :business_object_id, @business_objects_list, :id, :name  %>

Current value is displayed, available values are shown in the drop down list.

When applying a modification (not related to this drop down) which fails validation, Rails tries to render _form.html.erb, but raises an error due to missing @business_objects_list:

undefined method `map' for nil:NilClass

@business_objects_list is created in the private section of the business rules controller:

    # Retrieve business objects list
    def set_business_objects_list
      if action_name == 'edit'
        my_business_area = @business_rule.business_process.business_flow.business_area_id
      else
        my_business_area = BusinessProcess.find(params[:business_process_id]).business_flow.business_area_id
      end
      @business_objects_list = BusinessObject.where("business_area_id = ?", my_business_area)
end

The set_business_objects_list function is called at the top of the controller:

 before_action :set_business_objects_list, only: [:new, :edit]

EDIT: Controller actions

  # GET /business_rules/1/edit
  def edit
    ### Retrieved by Callback function
  end

  # PUT /business_rules/1
  # PUT /business_rules/1.json
  def update
    ### Retrieved by Callback function
    @business_rule.updated_by = current_user.user_name

    respond_to do |format|
      if @business_rule.update_attributes(business_rule_params)
        format.html { redirect_to @business_rule, notice: 'Business rule was successfully updated.' }
        format.json { head :no_content }
      else
        format.html { render action: "edit" }
        format.json { render json: @business_rule.errors, status: :unprocessable_entity }
      end
    end
end

Can you please help find out what's wrong here? Thanks!

Answer 1

undefined method `map' for nil:NilClass

You need to make @business_objects_list available to the update action as well because render action: "edit" just loads the edit.html.erb . So the scope of @business_objects_list is lost

Solution:

Just add the update action to the list of actions to the before_action :set_business_objects_list

before_action :set_business_objects_list, only: [:new, :edit, :update]