Rails: Possible to send a disabled option as a valid params value? - ruby-on-rails

Question

I have a User, and a Country models, and in User model, it has has_many :countries relationship. The country has 3 attributes -> :id, :name, :is_main
Let's say the countries table is currently populated as follow:
id name is_main
----------------------------------
1 USA true
2 Germany nil
3 France nil
4 England nil
Let's say a user is created that has countries USA, and Germany. So in this case the user.countries.pluck(:id) would return [1,2].
What I would like to achieve is that when editing the user's countries, a dropdown will appear and I am only allowed to add (or remove) countries where 'is_main' attribute is nil. In other words, in the dropdown, the USA country should either be disabled or be hidden completely to be selected. At the same time, the USA should remain in the user.countries after form submission plus any new countries that have been added from update action.
In short:
Original => user.countries.pluck(:id) => [1,2]
In edit form, if I add France to the user, the end result should be user.countries.pluck(:id) => [1,2,3]
I have tried the following:
f.collection_select(:countries, Country.where(is_main: nil), :id, :name, {}, {:multiple => true})
In doing this, the dropdown will display all the countries for me to add except for USA, which is what I desired. But the problem is when I click submit, the params[:country_ids] will be [2, 3]. As a result, after update action, the user.countries.pluck(:id) would become [2,3] instead of desired [1,2,3], effectively removing USA's id.
Is there a way to work around this? I have tried also adding :disabled option in collection_select that disables USA option, but the params[:country_ids] would still be [nil, 2, 3]. Appreciate if anyone could advise me on this.

Answer 1

I've come across this issue on my application. In rails 4+, set include_hidden attribute to false in multi-select selet_tags. Here's how i did it.
= f.input :countries, as: :select, collection: Country.where(is_main: nil).map{|country| [country.id, country.name]}, input_html: { multiple: true, data: { placeholder: "Countries"} }, include_hidden: false
Hope this helps you solve your issue

Answer 2

Actually using your example for multiple selection, your params after submit should have params[:country_ids] = [2,3]. If you are not giving the option to select USA, then it just won't be included.
You can disable options doing this:
// Your select id should be 'user_country_ids', if not change it
// This assumes that your first item will always be USA
$('#user_country_ids option:eq(0)').prop('disabled', true);
Anyway, this JS can be bypassed, so you will need to handle this on your backend too adding a validation for this in your User model:
class User
has_many :countries
validate :main_countries_always_associateds
private
def main_countries_always_associateds
errors.add(:countries, "must include main ones") if Country.where(is_main: true).any?{ |c| !self.countries.include? c }
end
end
EDIT:
If you want to always have main countries inside each user countries, then you can use before_validation callback to override this selection. I recommend to also include the disabled options on the multiple select, so the user is aware of this, the validation may become not necessary.
class User
has_many :countries
before_validation :associate_main_countries
# You should use something like this if you want your dropdown to always show marked main countries
def self.new_custom_user
User.new(countries: Country.where(is_main: true))
end
private
def associate_main_countries
Country.where(is_main: true).each do |c|
self.countries << c if !self.countries.include?(c)
end
end
end