问在rails中使用#includes，对Stocks表运行两次

EN

<% @portfolio.transactions.each do |trans| %>
  <tr>
    <td class="col-md-1"><%= trans.stock.symbol %></td>
    <td class="col-md-1"><%= number_to_currency(trans.stock.last_price) %></td>
    <td class="col-md-1"><%= trans.stock.name %></td>
    <td class="col-md-1"><%= trans.stock.stock_exchange %></td>
    <td class="col-md-1"><%= trans.num_of_shares %></td>
  </tr>
<% end %>

def show
  @portfolio = Portfolio.includes(:transactions, :stocks).find(params[:id])
  @transaction = Transaction.new
end

class Transaction < ActiveRecord::Base
  belongs_to :portfolio
  belongs_to :stock
end

class Stock < ActiveRecord::Base
  has_many :transactions
end

class Portfolio < ActiveRecord::Base
  belongs_to :user
  has_many :transactions
  has_many :stocks, through: :transactions
end

Started GET "/portfolios/2" for ::1 at 2016-09-24 17:59:13 -0400
Processing by PortfoliosController#show as HTML
  Parameters: {"id"=>"2"}
  Portfolio Load (0.2ms)  SELECT  "portfolios".* FROM "portfolios"
    WHERE "portfolios"."id" = $1 LIMIT 1  [["id", 2]]
  Transaction Load (0.4ms)  SELECT "transactions".* FROM "transactions"
    WHERE "transactions"."portfolio_id" IN (2)
  Stock Load (0.3ms)  SELECT "stocks".* FROM "stocks" WHERE
    "stocks"."id" IN (3, 1, 14, 9)
  Stock Load (0.3ms)  SELECT "stocks".* FROM "stocks"
  Rendered transactions/_form.html.erb (2.8ms)
  Rendered portfolios/show.html.erb within layouts/application (5.5ms)
  Rendered application/_nav.html.erb (0.7ms)
Completed 200 OK in 39ms (Views: 33.8ms | ActiveRecord: 1.1ms)