Ruby on Rails 按优先级排序

Question

以下是我获取国家和城市列表的查询：

@countries_cities = Product.joins(:user).where("country is not null and country <> ''").where("city is not null and city <> ''").where(:users => {:merchant_status => 1}).group(:country, :city).select("country,city").as_json

输出结果如下：

Object[city:"Bangkok",country:"Thailand"],Object[city:"Phuket",country:"Thailand"],Object[city:"Malaysia",country:"Kuala Lumpur"],Object[city:"Malaysia",country:"Penang"],Object[city:"Shanghai",country:"China"],Object[city:"Beijing",country:"China"]

cchs = @countries_cities.group_by{|cc| cc["country"]}
@search_location_country = cchs

而观点是：

    <ul id="color-dropdown-menu" class="dropdown-menu dropdown-menu-right" role="menu">
      <% @search_location_country.each do |country, cities| %>
        <li class="input" style="background:#ECECEC; "><a href="#" style="font-weight: bold;"><%= country.upcase %></a></li>
                <%  cities.each do |city| %>
        <li class="input"><a href="#"><%= city["city"].titleize %></a></li>
    <% end %>
   <% end %>
</ul>

现在下拉结果遵循以下模式：

Thailand
  -Bangkok
  -Phuket
Malaysia
  -Kuala Lumpur
  -Penang
China
  -Beijing
  -Shanghai

如何确保Malaysia 始终位于下拉列表的顶部？谢谢！！

Answer 1

怎么样：

@countries_cities = Product.joins(:user)
                           .where.not(country: [nil, ''])
                           .where(users: {merchant_status: 1})
                           .group(:country, :city)
                           .order("country!= 'Malaysia'")
                           .select(:country, :city)
                           .as_json

在 Postgres 中，false 排在 true 之前（在此处查看此答案：Custom ORDER BY Explanation）

Answer 2

您可以像这样自定义查询：

@countries_cities = Product.joins(:user)
                           .where.not(country: [nil, ''])
                           .where(:users => {:merchant_status => 1})
                           .group(:country, :city)
                           .order("ORDER BY 
                                   CASE WHEN country = 'Malaysia' THEN 1
                                   ELSE 2
                                   END ASC")
                           .select(:country, :city)
                           .as_json

所以我们设置了马来西亚 = 2，其他 = 1 的顺序，以确保马来西亚的结果会在最前面。