未定义的方法 `[]' for nil:NilClass Ruby Object in lib Rails

Question

我有一个形式相当复杂的应用程序，它使用 lib 文件夹中的 Ruby 对象（我第一次使用 ruby​​ 对象）。我无法弄清楚如何在我的更新嵌套属性表单中创建多个 :task_ids，即使参数是在我的 Ruby 对象自定义类中定义的（这是我第一次使用它，我正在学习如何调用它）。我不断收到此错误：

undefined method `[]' for nil:NilClass

我的表单试图做的是基于预制的“模板”任务和里程碑创建启动任务和启动里程碑。因此，当用户创建项目时，他们已经添加了一些常见任务。此代码直接与上一个问题和答案相关： Add Multiple Nested Attributes through checkboxes Rails 4 (maybe with multiple forms)

我的控制器：

class ProjectsController < ApplicationController

def new_milestones
    @project.milestones.build
    @project.tasks.build
    @milestones_templates = MilestoneTemplate.where(template_id: @project.template_id)
  end

 def update
    respond_to do |format|
      result = ProjectUpdater.perform(@project, update_params) == true
      if result == true
        format.html { redirect_to @project, notice: 'Project was successfully updated.' }
        format.json { render :show, status: :ok, location: @project }
      else
        @project = result
        format.html { render :edit }
        format.json { render json: @project.errors, status: :unprocessable_entity }
      end
    end
  end

  def project_params
      params.require(:project).permit(:id, :name, :template_id, milestone_attributes:[{:names => []},  {:ids => []}, { :milestone_ids => []},:id, :name, :project_id, :milestone_template_id, :project_id, task_attributes: [{:names => []},  {:ids => []}, { :task_ids => []}, :id, :name, :milestone_id, :task_template_id, :project_id, :_destroy]])
    end
  end

lib/project_updater.rb

class ProjectUpdater

  def self.perform(project, params)
    **milestones = params[:project][:milestones]** <--- this is the line where the error is
    #Create and save each milestone
    # You might be able to us nested attributes to save tasks.

    if project.update_attributes(params[:project])
      return true
    else
      return project
    end
  end
end

我的表格

<%= form_for @project do |f| %>
  <% @milestones_templates.each_with_index do |milestone, index| %>
    <br>
    <%= f.fields_for :milestones, index: index do |fm| %>
      <%= fm.hidden_field :name, value: milestone.name %>
      <!-- Create a checkbox to add the milestone_id to the project -->
      <%= fm.label milestone.name %>
      <%= fm.check_box :milestone_template_id,{}, milestone.id %>
      <br>
      <% milestone.task_templates.each_with_index do |task, another_index| %>
        <%= fm.fields_for :tasks, index: another_index do |ft| %>
          <!-- Create a checkbox for each task in the milestone -->
          <%= ft.label task.name %>
          <%= ft.check_box :task_ids, {}, task.id %>
        <% end %>
      <% end %>
      <br>
    <% end %>
  <% end %>
  <br>
<%= f.submit %>
  <% end %>

提交的内容：

{"utf8"=>"✓", "_method"=>"patch", "authenticity_token"=>"do/NeMW4wvsh8PCOIYAvuDiH0DwKVr6v0Sm55gOuCHM/Fw5h9T0orRjrspcQpNSx5Vp2JOmtVf+3O18P2XB4vA==", "project"=>{"milestones"=>{"0"=>{"name"=>"Yellow Milestone 1", "milestone_template_id"=>"18", "tasks"=>{"0"=>{"task_ids"=>"1"}, "1"=>{"task_ids"=>"0"}, "2"=>{"task_ids"=>"0"}}}, "1"=>{"name"=>"Yellow Milestone 2", "milestone_template_id"=>"0", "tasks"=>{"0"=>{"task_ids"=>"0"}, "1"=>{"task_ids"=>"0"}, "2"=>{"task_ids"=>"0"}}}, "2"=>{"name"=>"Yellow Milestone 3", "milestone_template_id"=>"0", "tasks"=>{"0"=>{"task_ids"=>"0"}, "1"=>{"task_ids"=>"0"}, "2"=>{"task_ids"=>"0"}}}}}, "commit"=>"Update Project", "controller"=>"projects", "action"=>"update", "id"=>"155"}

config/application.rb

require File.expand_path('../boot', __FILE__)

require 'rails/all'

Bundler.require(*Rails.groups)


module Taskit


    class Application < Rails::Application

        config.autoload_paths += %W(#{config.root}/lib)
        config.active_record.raise_in_transactional_callbacks = true
      end


    end

Answer 1

首先我认为这行有一个错字：

result = ProjectUpdater.perform(@project, update_params)

我没有看到update_params 方法，所以我认为这应该是project_params。

ProjectUpdater 中的问题是因为params.require(:project) 返回一个没有外部 :project 键的哈希，所以在ProjectUpdater.perform 方法中去掉 :project 键：

milestones = params[:milestones]