Question

我有以下型号。

class Candidate <  ActiveRecord::Base
  belongs_to :accommodation
  has_many :rates, :foreign_key => :candidate_id
end

class Accommodation < ActiveRecord::Base
  has_many :rates, :through => :candidates
end

class Rate < ActiveRecord::Base
  belongs_to :candidate
  delegate :accommodation, :to => :candidate
end

class City < Location
  has_and_belongs_to_many :accommodations, :foreign_key => 'location_id'
end

现在我获得了所有位置，以便迭代它们并获得所有位置及其住宿和费率。问题是我希望只有最近的住宿费率，但是按照名为：supplier_id的列分组在我看来：

 <% acc.rates.each do |rate| %>
                  <div class="rate">
                    <div class="">
                      <h3>
                        <%= rate.promo %>
                        <small><%= rate.supplier %></small>
                        <span class="rate-price text-right"><strong><%= rate.try(:nightly_rate).try(:ceil) %></strong></span>
                        <small>€</small>
                      </h3>
                    </div>
                  </div>

              <% end  %>

那么我怎样才能获得每个供应商的最新费率（按供应商分组），以一种我可以加载的方式，否则性能会太慢。

Answer 1

我认为您需要在2个单独的查询中划分此查询：

locations = Location.includes(:accomodations)
accomodation_ids = locations.map(&:accomodation_ids).flatten
rates = Rate.by_accomodation_and_supplier(accomodation_ids)

class Rate    
  def self.by_accomodation_and_supplier(accomodation_ids)
    joins(candidate: { accomodation: accomodation_ids}).
      order(created_at: :desc).group(:supplier_id)
  end
end

如何获取关联组中的最新记录

1 个答案: