Question

我在calculation_of_total_cost

中有一个名为model Tippy的方法

它遇到了index.html.erb通过tippies个视图目录调用的问题。

这是我收到的错误：undefined method *＆＃39;为零：NilClass`

我用谷歌搜索过，现在明白这是其中一个变量为nil的结果。

如何解决此问题，即如何使方法在index.html.erb中运行？这是我从中调用它的索引视图，所以我需要一个实例方法，而不是类，对吧？

另外，附录：这个方法在show.html.erb

中工作正常

show.html.erb

<br/><br/>
<h1 class="text-center">Your Total Cost</h1>
<br/><br />


<table class="table table-striped">
    <tr>
        <td>
            Cost of Your Meal:
        </td>
        <td>
            <%= humanized_money_with_symbol @tippy.cost %>
        </td>
    </tr>
    <tr>
        <td>
            Tip You Picked:
        </td>
        <td>
             <%= number_to_percentage(@tippy.tip * 100, format: "%n%", precision: 0) %>
        </td>
    </tr>
    <tr>
        <td>
            The Total Cost:
        </td>
        <td>
            <%= humanized_money_with_symbol @tippy.calculation_of_total_cost %>
        </td>
    </tr>
</table>


<%= link_to 'New Tippy', new_tippy_path %>

<%= link_to "Index", tippies_path %>

以下是Tippy型号：

class Tippy < ApplicationRecord

    validates :tip, presence: true
    validates :cost, presence: true

    #monetize :tip_cents
    monetize :cost_cents, :numericality => {:greater_than => 0}


    TIP_CHOICES = { "10%" => ".10", "20%" => ".20", "30%" => ".30", "40%" => ".40", "50%" => ".50", 
                    "60%" => ".60", "70%" => ".70", "80%" => ".80", "90%" => ".90" }

    def calculation_of_total_cost 
        cost + (tip * cost)
    end

end

以下是index.html.erb文件

<p id="notice"><%= notice %></p>

<h1>Tippies</h1>

<table>
  <thead>
    <tr>
      <th>Tip</th>
      <th>Cost</th>
      <th>Total</th>
      <th colspan="3"></th>
    </tr>
  </thead>

  <tbody>
    <% @tippies.each do |tippy| %>
      <tr>
        <td><%= tippy.tip %></td>
        <td><%= tippy.cost %></td>
        <td><%= tippy.calculation_of_total_cost %></td>
        <td><%= link_to 'Show', tippy %></td>
        <td><%= link_to 'Edit', edit_tippy_path(tippy) %></td>
        <td><%= link_to 'Destroy', tippy, method: :delete, data: { confirm: 'Are you sure?' } %></td>
      </tr>
    <% end %>
  </tbody>
</table>

<br>

<%= link_to 'New Tippy', new_tippy_path %>

Tippy Controller

class TippiesController < ApplicationController
  #before_action :set_tippy, only: [:show, :edit, :update, :destroy]

  # GET /tippies
  # GET /tippies.json
  def index
    @tippies = Tippy.all
  end

  # GET /tippies/1
  # GET /tippies/1.json
  def show
    #@calculation_of_total_cost 
  end

  # GET /tippies/new
  def new
    @tippy = Tippy.new
  end

  # GET /tippies/1/edit
  def edit
  end

  # POST /tippies
  # POST /tippies.json
  def create
    @tippy = Tippy.new(tippy_params)

    respond_to do |format|
      if @tippy.save
        format.html { redirect_to @tippy, notice: 'Tippy was successfully created.' }
        format.json { render :show, status: :created, location: @tippy }
      else
        format.html { render :new }
        format.json { render json: @tippy.errors, status: :unprocessable_entity }
      end
    end
  end

  # PATCH/PUT /tippies/1
  # PATCH/PUT /tippies/1.json
  def update
    respond_to do |format|
      if @tippy.update(tippy_params)
        format.html { redirect_to @tippy, notice: 'Tippy was successfully updated.' }
        format.json { render :show, status: :ok, location: @tippy }
      else
        format.html { render :edit }
        format.json { render json: @tippy.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /tippies/1
  # DELETE /tippies/1.json
  def destroy
    @tippy.destroy
    respond_to do |format|
      format.html { redirect_to tippies_url, notice: 'Tippy was successfully destroyed.' }
      format.json { head :no_content }
    end
  end

  private
    # Use callbacks to share common setup or constraints between actions.
    def set_tippy
      @tippy = Tippy.find(params[:id])
    end

    # Never trust parameters from the scary internet, only allow the white list through.
    def tippy_params
      params.require(:tippy).permit(:tip, :cost)
    end
end

Answer 1

要解决这个问题，你需要在index.html.erb的这一行设置 binding.pry 或断点，以便我们可以在循环中理解你正在执行为什么tippy正在获取价值为零。您需要安装pry gem。还请分享@tippies的值和循环中失败的另一个变量的细节，因为tippy = nil。 pry的替代方法是使用puts tippy.calculation_of_total_cost在日志中打印变量的值。

现在我猜我的@tippies表中包含所有@tippy的{{1}}可能有一个tippies字段。要验证这一点，您应该在calculation of total cost = nil视图中使用调试检查tippy和tippy.calculation_of_total_cost的值。

index.html.erb

最好还是检查<% @tippies.each do |tippy| %> <tr> <% binding.pry %> <td><%= tippy.tip %></td> <td><%= tippy.cost %></td> <td><%= tippy.calculation_of_total_cost %></td> <td><%= link_to 'Show', tippy %></td> <td><%= link_to 'Edit', edit_tippy_path(tippy) %></td> <td><%= link_to 'Destroy', tippy, method: :delete, data: { confirm: 'Are you sure?' } %></td> </tr> <% end %>是否有效。

show.html.erb

在视图中从模型类运行未定义的方法

1 个答案: