Rails has_many update with empty array - ruby-on-rails

Question

There is the following form code:
= form_for #task, html: { class: 'form-horizontal' } do |f|
.form-group
.col-sm-9.col-sm-offset-3
= render partial: 'shared/form_errors', locals: { subject: #task }
.form-group
label.col-sm-3.control-label for='title' Title
.col-sm-9
= f.text_field :title, class: 'form-control', placeholder: 'Title'
.form-group
label.col-sm-3.control-label for='description' Description
.col-sm-9
= f.text_area :description, class: 'form-control', placeholder: 'Description'
.form-group
label.col-sm-3.control-label Teams
.col-sm-9
ul
- Team.all.each do |t|
li
= check_box_tag "team_ids", t.id, #task.teams.include?(t), name: 'task[team_ids][]'
= t.name
.form-group
.col-sm-9.col-sm-offset-3
= f.submit 'Save', class: 'btn btn-success'
As you can see I can select team for my task through checkboxes. My controller:
def update
#task = Task.find(params[:id])
if #task.update(task_params)
redirect_to tasks_path, flash: { alert: TASK_UPDATING_MESSAGE }
else
render 'edit'
end
end
private
def task_params
params.require(:task).permit(:title, :description, team_ids: [])
end
It works good if I update task with some checked teams; but also I want to have ability to check no teams and update taks with empty array of teams. But in this case tasks_params doesn't have team_ids array, and updating doesn't work. How can I fix it? Thanks!

Answer 1

My understanding is that when you submit your form with nothing checked, you have params[:task][:team_ids] = nil.
You can try something like:
def task_params
params[:task][:team_ids] = [] if params[:task][:team_ids].nil?
params.require(:task).permit(:title, :description, team_ids: [])
end

Answer 2

You can do it using collection_check_boxes, just replace the list of teams with:
ul
= f.collection_check_boxes :team_ids ,Team.all, :id, :name do |b|
= content_tag :li, raw("#{b.label { b.check_box } }" + b.object.name)
And this will do the trick.
Note: With this Rails add a hidden field, which fix your issue, also you will fix it only with this:
<input type="hidden" name="task[team_ids][]" value="" autocomplete="off">