How to use :selected with grouped_collection_select

问题

Is it possible to somehow use the :selected option that you'd use on a normal select view helper with the grouped_collection_select function? I'd like to set the value that gets pre-selected in my list. I've tried passing in :selected as an option with no luck!

Here's some code snippts of my tests:

grouped_collection_select 'user[subscription_attributes]', :subscription_plan_id, Trade.order(:name).all, :subscription_plans, :name, :id, :display_name, { :include_blank => true, :selected => 5 }

grouped_collection_select 'user[subscription_attributes]', :subscription_plan_id, Trade.order(:name).all, :subscription_plans, :name, :id, :display_name, :include_blank => true, :selected => 5 

Neither version works. No selected is set. I'm using this to set a value for a nested model. I'm using the railscasts dynamic select list methods: http://railscasts.com/episodes/88-dynamic-select-menus-revised

I couldn't get formtastic to play nicely with the group selects so I had to do it by hand but I don't keep this value selected when a user fails validations. I'd like to keep this set when they fix validation errors.

回答1:

I just ran across the same problem and solved it using the option_groups_from_collection_for_select helper and the select helper documented at: http://api.rubyonrails.org/classes/ActionView/Helpers/FormOptionsHelper.html.

The first step is to create the grouped options. Taking your example, it should look like:

<% options = option_groups_from_collection_for_select(Trade.order(:name).all,
   :subscription_plans, :name, :id, :display_name, 5) %>

Then I created the select object like:

<%= select('user[subscription_attributes]', :subscription_plan_id, options, 
  include_blank: true) %>

You could write it all out in one line, I just broke out the options into a separate variable to illustrate the two different methods.

回答2:

Maybe too late, but the API documentation of grouped_collection_select states: 'The value returned from calling method on the instance object will be selected.'

So, you don't even have to specify a :selected option, since Rails will automatically select based on the current value of your attribute. If subscription_plan_id has value 5, then that's what will be selected.

If that's supposed to be a default value, then you can set it with an after_initialize in your model.

回答3:

Actually you need to send in options include_blank for example

<%= grouped_collection_select :id, model.all, options = {:include_blank => 'Selecione'}%>

来源：https://stackoverflow.com/questions/11817496/how-to-use-selected-with-grouped-collection-select