Display a checkbox list instead of multiple select - ruby-on-rails

Question

I have a model MyModel with a serialized attribute a, describing an array of symbols.
This code works :
<% form_for #my_model do |f| %>
<%= f.select :a, MyModel::AS, :multiple => true) %>
<% end %>
The parameters are correct :
{ :my_model => { :a => [:a_value1, :a_value2] } }
I want to transform this multiple select into a set of checkboxes, like this :
<% form_for #my_model do |f| %>
<% MyModel::AS.each do |a_value|
<%= f.check_box(:a_value) %>
<% end %>
<% end %>
It works too, but the parameters are not the same at all :
{ :my_model => { :a_value1 => 1, :a_value2 => 1 } }
I think of 2 solutions to return to the first solution...
Transform my check_box into check_box_tag, replace multiple select, and add some javascript to 'check' select values when user clic on check_box_tags. Then, the parameter will be the same directly in the controller.
Add a litte code into the controller for 'adapting' my params.
What solution is the less ugly ? Or is there any other one ?

Answer 1

I found a solution, using 'multiple' option that I didn't know.
<% MyModel::AS.each do |a_value| %>
<%= f.check_box(:a, { :multiple => true }, a_value) %>
<% end %>
Result parameters are a little weird, but it should work.
{"my_model" => { "a" => ["0", "a_value1", "0", "a_value2", "0"] }
Edit from #Viren : passing nil at the end of the function like
<%= f.check_box(:a, { :multiple => true }, a_value, nil) %>
works perfectly.

Answer 2

There is another solution worth mentioning that makes it very easy to insert records into the database if you have a has_and_belongs_to_many or has_many through relationship by using the collection_check_boxes form helper. See documentation here.
<%= f.collection_check_boxes :mymodel_ids, MyModel::AS, :id, :name do |m| %>
<%= m.check_box %> <%= m.label %>
<% end %>
Then, in the controller we would allow the mymodel_ids attribute:
params.require(:mymodel).permit(:name, mymodel_ids:[])
We can also set up a model validation to require that at least one of the checkboxes be checked:
validates :mymodel_ids, presence: true
An added benefit of this method is that if you later edit the mymodel record and uncheck one of the checkboxes, its record will be deleted from the many_to_many association table on save.

Answer 3

You can do it like this:
<% MyModel::AS.each do |a_value| %>
<%= f.check_box("a[]", a_value) %>
<% end %>
This will make params come to server as follows
{ :my_model => { :a => [:a_value1, :a_value2] } }

Answer 4

if you already have a select_tag
<%= select_tag "filters", options_from_collection_for_select(filter_values, "id", "name", selected_ids), multiple:true, class:"form-control" %>
and wants to replace it with check_box_tag, you will need to implement something like this:
<div class="checkbox-inline">
<%= check_box_tag "filters[]", value.id, selected_ids.include?(value.id), { :multiple => true} %>
<%= value.name %>
</div>
notice the ending brackets on the name which is needed to catch check box results in the same parameter.
When I implemented this, the parameters were of the same format between the select_tag and the check_box_tag