Ruby on Rails: Keep check boxes selected after search - ruby-on-rails

Question

In my RoR application I have a form whereby users can search for their contacts by first name and select the ones that they want to send an email to. My problem is that after searching for say "Tom", and selecting the checkbox for "Tom", if they then reset the search to display all check boxes "Tom" is no longer selected.
Can someone please tell me how this can be sorted?
The code in the view is:
<div class="panel-body">
<%= form_tag '/emails/contact_search', :method => 'get' do %>
<p>
<%= text_field_tag :search_string, params[:search_string], :placeholder => "Search by firstname" %>
<%= submit_tag "Search" %>
</p>
<% end %>
<%= form_for(#email) do |f| %>
<fieldset>
<div class="form-group">
<label>From Email Address</label></br>
<% #useraccounts.each do |useraccount| %>
<%= f.radio_button :account_id, useraccount.account_id, :checked => false %>
<%= f.label :account_id, useraccount.account.email, :value => "true" %><br>
<% end %>
</div>
<div class="form-group">
<label>Contacts</label></br>
<%= f.collection_check_boxes :contact_ids, #contacts, :id, :fullname, checked: #selected_contact_ids %>
</div>
<div class="form-group">
<label>Groups</label></br>
<%= f.collection_check_boxes :group_ids, Group.where(user_id: session[:user_id]), :id, :name ,{ prompt: "name" } %>
</div>
<div class="form-group">
<label>Attachment</label>
<%= f.file_field :attachment, :size => 42 %><br>
</div>
<div class="actions">
<%= f.submit "Continue", {:class => 'btn btn-primary '} %>
<%= render "/error_messages", :message_header => "Cannot save: ", :target => #email %>
</div></br>
</fieldset>
<% end %>
</div>
The controller code for the search is:
def contact_search
#email = Email.new(session[:email_params])
#email.current_step == session[:email_step]
#useraccounts = Useraccount.where(user_id: session[:user_id])
#contacts = Contact.contact_search(params[:search_string])
if #contacts.empty?
flash[:notice] = "There are no emails with that subject"
#contacts = Contact.all
end
render :action => "new"
end
private
def email_params
params.require(:email).permit(:subject, :message, :account_id, { contact_ids: [] }, { group_ids: [] }, :attachment)
end
And in the model:
def self.contact_search(search_string)
self.where("firstname LIKE ?", search_string)
end
I cannot work out how to keep a checkbox selected after a user then searches for something else or resets the search, can someone please shed some light on how this can be achieved?

Answer 1

This seems to be one of those obscure and badly documented features of Rails. What has to be done is pass an array if ids to be checked into the checked parameter
= f.collection_check_boxes :contact_ids, #contacts, :id, :fullname, checked: #selected_contact_ids
and then check boxes with items of id 1, 2 and 3 will be checked. You will need to pass this array obviously from the controller somehow. E.g.
#selected_contact_ids = email_params.fetch(:contact_ids, [])