将下拉菜单重置为所选值

Question

我有一个显示数据库中所有行程的索引页面。页面顶部是一个带有下拉列表的过滤器，您可以在其中选择类别、地区或两者来过滤结果。

当您选择您的选项并单击“显示”时，下拉菜单会返回到“所有类别”和“所有地区”的默认选项。

当我过滤结果时，如何才能让选定的选项显示在下拉列表中？

这是我的下拉菜单：

.row
  = form_tag all_road_trips_path, id: 'filter-trips-form', method: :get do
  .select-intro
    Browse
  .select-wrapper.trip-categories
    = collection_select(:category, :id, Category.all, :id, :name, :prompt => "All categories")
  .select-intro
    trips for
  .select-wrapper
    = collection_select(:region, :id, Region.all, :id, :name, :prompt => "All regions")
  .select-button
    = submit_tag 'Show Trips', class: 'button square'

编辑::

我尝试添加selected 值并得到一个'undefined method `[]' for nil:NilClass' 错误。我认为这是因为我的下拉列表的第一个值是“所有类别”，实际上并不是数据库中的对象，因此缺少 id。这是更新的代码和服务器输出：

.row
  = form_tag all_road_trips_path, id: 'filter-trips-form', method: :get do
  .select-intro
    Browse
  .select-wrapper.trip-categories
    = collection_select(:category, :id, Category.all, :id, :name, :prompt => "All categories", :selected => params[:category][:id])
  .select-intro
    trips for
  .select-wrapper.trip-regions
    = collection_select(:region, :id, Region.all, :id, :name, :prompt => "All regions", :selected => params[:region][:id])
  .select-button
    = submit_tag 'Show Trips', class: 'button square'

和

Started GET "/road-trips/all" for 127.0.0.1 at 2014-01-10 14:03:39 -0600
Processing by RoadTripsController#all as HTML
  Category Load (0.4ms)  SELECT "categories".* FROM "categories"
  Rendered road_trips/_trip_filter.html.haml (4.7ms)
  Rendered road_trips/all.html.haml within layouts/application (5.6ms)
Completed 500 Internal Server Error in 9ms
  User Load (0.4ms)  SELECT "users".* FROM "users" WHERE "users"."id" = 1 LIMIT 1

NoMethodError - undefined method `[]' for nil:NilClass:
  app/views/road_trips/_trip_filter.html.haml:6:in `block in _app_views_road_trips__trip_filter_html_haml__2571960046883419269_70320079055780'
  haml (3.1.8) lib/haml/helpers/action_view_mods.rb:162:in `block (2 levels) in form_tag_with_haml'

Answer 1

使用:selected 选项：

= collection_select(:category, :id, Category.all, :id, :name, :prompt => "All categories", :selected => params[:category_id or however you store this value])

在此处底部评论中简要讨论：http://apidock.com/rails/ActionView/Helpers/FormOptionsHelper/collection_select

发生了什么：通过将一个值传递给collection_select 表单助手的:selected 选项，您是在告诉它在值匹配时将其中一个选项标签标记为选中。例如，给定选项“苹果”、“香蕉”、“巧克力”：

<select name="treat">
  <option value="apple">Apple</option>
  <option value="banana">Banana</option>
  <option value="chocolate">Chocolate</option>
</select>

当您将“巧克力”传递给collection_select 表单助手时，它会将值与选项标签的值匹配，并将匹配的标签标记为选中：

= collection_select :treat, args..., :selected => 'chocolate'
# will render:
<select name="treat">
  <option value="apple">Apple</option>
  <option value="banana">Banana</option>
  <option value="chocolate" selected>Chocolate</option>
</select>

希望对您有所帮助。

编辑： 您错误地调用了 params 值，而不是：

params[:category][:id]

应该是：

params[:category_id]

这也适用于其他参数。

这是因为表单助手：collection_select :category, :id 将生成一个名为 category_id 的选择标记，这将是提交的参数。

no method [] for nilClass 错误是由 params[:category] 返回 nil 引起的，因为没有这样的参数。