Rails 5 form_for with checkbox array - ruby-on-rails

Question

I am using a PostgreSQL database and Rails 5.0.6.
I try to build a course allocation WebApp for the school where I am working. For each course the teachers are able to select which forms are allowed to visit the course.
Migration file:
def up
create_table :courses do |t|
t.integer :number, null: false
t.string :name, null: false
t.text :description, null: false
t.decimal :level, array: true, default: []
t.integer :max_visitor, null: false
t.integer :min_visitor
t.integer :pos_visit
t.timestamps
end
end
In my Controller:
params.require(:course).permit(:number, :name, :description, :level [], :max_visitor, :min_visitor, :pos_visits)
I already read this post: Rails 5 strong params with an Array within check boxes values. But the Syntax params.require(:product).permit(:id, **category_ids: []**) doesnt work for me even though I am using rails 5 as well. I am not sure if :level [] really works but it seems to be correct syntax.
This is my Form:
<%= form_for #course do |t| %>
<%= t.text_field :number, class: 'form-control' %>
<%= t.text_field :name, class: 'form-control' %>
<%= t.text_area :description, class: 'form-control' %>
<%= t.check_box :level[], 1%>
<%= t.check_box :level[], 2%>
<%= t.check_box :level[], 3%>
<%= t.check_box :level[], 4%>
<%= t.text_field :max_visitor, class: 'form-control' %>
<%= t.text_field :min_visitor, class: 'form-control' %>
<%= t.text_field :pos_visit, class: 'form-control' %><br/>
<%= t.submit "bestätigen", class: "btn btn-success"%>
<% end %>
This check_box syntax seems to be wrong.
May anyone help me with the right syntax of the check_boxes?
Thanks for help.

Answer 1

There's a collection_check_boxes helper method for this:
<%= form_for #course do |f| %>
<%= f.collection_check_boxes(:level, { 'One': 1, 'Two': 2, 'Three': 3 }, :last, :first) %>
<% end %>
The third argument is the method used to get the value from the "collection", and the fourth is the method used to get the label from the "collection". This helper method automatically converts the Hash into an array, that's why I'm using last and first here.
It's also possible to style it the way you want e.g. using Bootstrap:
<%= f.collection_check_boxes(:level, { 'One': 1, 'Two': 2, 'Three': 3 }, :last, :first) do |b| %>
<div class="form-check form-check-inline">
<%= b.check_box class: 'form-check-input' %>
<%= b.label class: 'form-check-label' %>
</div>
<% end %>

Answer 2

<%= check_box_tag 'level[]', 1%>
<%= check_box_tag 'level[]', 2%>
<%= check_box_tag 'level[]', 3%>
<%= check_box_tag 'level[]', 4%>
But when you use check_box_tags in form_for, then the parameters level[], will be outside off the strong parameters array you usually use in the controller#new function.
Parameters: {"course"=>{"number"=>"12", "name"=>"tanzen", "description"=>"efwefggw", "max_visitor"=>"12", "min_visitor"=>"5", "pos_visit"=>"2"}, "level"=>["1", "3", "4"], "commit"=>"bestätigen"}
So I added the level manually
#course = Course.new(course_params)
#course.level = params[:level]