如何在rails one_to_many关联中执行计算？

Question

项目与财务有一对多关联

财务与付款里程碑具有一对多关联

每个付款里程碑都有一个字段amount_invoice和amount_realized。现在我想计算所有payment_milestone的amount_invoice和amount_realized的差值，然后求和并在project＃index中显示它们。我试过了但是我出错了这是我尝试的代码-

<% @projects.each do |project| %>
    <% @financials = Financial.where(project_id: project.id) %>
    <%  @Payment_milestones = PaymentMilestone.where(financial_id: @financials.ids) %>

    <%  outstanding_payment = 0 %>
    <%  @Payment_milestones.each{|s| outstanding_payment += s.amount_invoiced-s.amount_realized if s.amount_invoiced > s.amount_realized } %>
    <% @outstanding_payment = outstanding_payment %>
    <td><%= @outstanding_payment %></td>
<% end %>

Answer 1

由于s.amount_invoiced为零，您得到了错误。>

是否有可能将amount_invoiced和amount_realized的默认值设置为0？（由于[C​​0]不能与nil一起使用，而不能用于整数或浮点数）

OR

您可以将代码更改为：<