Return an array using `form_with`?

In my view, I have several checkboxes, and I want to send back an array of which are checked. I have achieved this by writing the HTML myself, but I'm wondering if there's a way to do it using FormBuilder#check_box.

What I have working

<%= form_with model: @dog, local: true do |my_form| %>
  <label>
    <input type="checkbox"
           name="dog[breeds][]"
           value="labrador">
    Labrador
  </label>
  <label>
    <input type="checkbox"
           name="dog[breeds][]"
           value="husky">
    Husky
  </label>
    <%= my_form.submit 'Save' %>
<% end %>

This works perfectly: the params contain what I expect. If I check the "husky" box and submit, the "breeds" array contains "husky":

"dog"=>{"breeds"=>["husky"]}

But I want to know if there's a way to use my_form.check_box for this, instead of writing out the checkbox HTML myself.

What I've tried for FormBuilder#check_box

<%= form_with model: @dog, local: true do |my_form| %>
  <label>
    <%= my_form.check_box 'breeds[]', value: 'labrador'%>
    Labrador
  </label>
  <label>
    <%= my_form.check_box 'breeds[]', value: 'husky'%>
    Husky
  </label>
  <%= my_form.submit 'Save' %>
<% end %>

This doesn't submit what I expect. In the params, no matter which boxes I check, the "breeds" array is always empty:

"dog"=>{"breeds"=>[]}

Is there a way to do use the FormBuilder helpers for what I'm trying to do?

It really seems like there should be, but I've not been able to find it anywhere.

You should be able to do this like so:

<%= form_with model: @dog, local: true do |my_form| %>
  <% ['labrador','husky'].each do |breed| %>
      <%= my_form.check_box :breeds, {multiple: true}, breed%>
      <%= my_form.label :breeds, breed.titleize %>
  <%end%>
  <%= my_form.submit 'Save' %>
<% end %>

The signature for check_box is (object_name, method, options = {}, checked_value = "1", unchecked_value = "0").

Since you are using the form builder the object_name can be omitted as it will be my_form.

So we pass:

• the method :breeds,
• the options {multiple: true} so that it creates a collection
• the checked_value will be the breed name.

ActionView::Helpers::FormHelper#check_box Documentation