如何使用 Kaminari Gem 计算所有分页页面的总金额？

Question

我在使用 Kaminari Gem 进行分页时遇到问题，我想计算应用程序中所有费用的总和，但是，在我看来，我只能获得当前查看的单个分页页面的总费用。如何计算所有分页页面的总费用？

在我的控制器中

def index
 @expenses = Expense.order(:batch_id).page(params[:page])
 @total_expenses = @expenses.map(&:total).sum
end

在我的模型中，我已经分配了我想要的每页

class Expense < ApplicationRecord
  belongs_to :batch

  paginates_per 10

  def total
    unit_price.to_i * quantity.to_i
  end
end

在我看来

 <div>
   <table>
     <thead>
       <tr>
         <th></th>
         <th>Batch No.</th>
         <th>Date</th>
         <th>Category</th>
         <th>Quantity</th>
         <th>Unit Price</th>
         <th>Total Expense</th>
         <th>Description</th>
         <th>Action</th>
        </tr>
        </thead>
        <tbody>
          <% @expenses.each do |expense| %>
            <tr>
              <td>
                <div>
                  <input id="checkbox-table-search-1">
                  <label for="checkbox-table-search-1">checkbox</label>
                </div>
              </td>
                <th><%= expense.batch.batch_no %></th>
                <td><%= expense.date.strftime('%d %b %Y') %></td>
                <td><%= expense.category %></td>
                <td><%= expense.quantity %></td>
                <td><%= expense.unit_price %></td>
                <td><%= number_to_currency(expense.total, :unit => "") %></td>
                <td><%= expense.description %></td>
                <td><%= link_to "Show", expense %>
                    <%= link_to 'Edit', edit_expense_path(expense) %>
                    <%= link_to 'Destroy', expense, data: { turbo_method: "delete", turbo_confirm: 'Are you sure?' }%>
                </td>
            </tr>
          <% end %>
      </tbody>
   </table>
</div>

<div>
 Total Expense per page = <%= number_to_currency(@total_expenses, :unit => "Tshs. ", :delimiter => ",") %>
</div>


<div>
 <%= paginate @expenses %>
</div>

Answer 1

我更喜欢使用 SQL

sum

。您可以在这里阅读更多内容。使用

map

，所有记录都必须在计算之前加载到内存中。

 # you can also group, or adding conditions before calculation
 @total_expenses = Expense.sum("unit_price*quantity")
 # or
 @total_expenses = Expense.group("category").sum("unit_price*quantity")