Rails: default selection if nothing has been selected in check_box_tag

Question

I have an app where a user can enter a project into a database.

There is an option where they can select a number of different technologies for their project. At the moment, the app flags up an error if the user doesn't select at least 1 technology.

I am wanting to change this so that if they don't select a technology, it automatically goes down as "other" instead.

Here is my project controller actions, new and create:

def new
    @project = Project.new
        @technol = Technol.new(params[:tech])

        @all_technols = Technol.order('tech ASC') 
        @all_technols = Technol.all
        tech_ids = params[:technols][:id].reject(&:blank?) unless params[:technols].nil?


        @project_technol = @project.projecttechnols.build

    respond_to do |format|
      format.html # new.html.erb
      format.json { render json: @project }
    end
  end



def create  
    @project = Project.new(params[:project])
        @project.client = params[:new_client] unless params[:new_client].blank?
        @project.industry = params[:new_industry] unless params[:new_industry].blank?
        @project.business_div = params[:new_business_div] unless params[:new_business_div].blank?


if !params[:technols].nil?

            params[:technols][:id].each do |tech|


                if !tech.empty?

                    @project_technol = @project.projecttechnols.build(:technol_id => tech) 
                    end
            end

end

Here is the new view for the technology field

<ul> 


<% @all_technols.each do |technol| %> 



<li class="split"> 
<%= check_box_tag "project[technol_ids][]", technol.id,  @project.technols.include?(technol) %> 
<%= technol.tech %> 
</li> 

<% end %>
</ul> 

The technology ID for "other" in the technols table is "18". So is there a way to say that if no technology is chosen, then :technol_id => ["18"].

I was given help earlier, and it was suggested that I should add this:

def create
  ...
  technol_ids = params[:technol_ids].blank? ? [18] : params[:technol_ids]
  technol_ids.each do |id|
  ...
  end
  ...
end

I am having trouble getting this to work. I don't think I am putting it in the right bit of my code. I'm still new to rails, so please remember this when trying to help. Thanks very much

EDIT

With no technols_id selected

Processing by ProjectsController#create as HTML
  Parameters: {"utf8"=>"Ô£ô", "authenticity_token"=>"8Hgc1GXqNhWkzO3Wgkfpf6z+fdImf6QvAv0XLbP0a5g=", "project"=>{"project
_name"=>"Test", "archive"=>"0", "username"=>"test", "status"=>"Active", "exception_pm"=>"", "client"=>"", "business_d
iv"=>"", "project_owner"=>"", "start_date"=>"11-12-2012", "first_name"=>"test", "last_name"=>"test", "fullname"=>
"test test", "entry_date"=>"2012-11-26", "end_date"=>"19-12-2012", "techinfo"=>"Test", "role"=>"", "industry"=>""
, "summary"=>"Test", "lessons_learned"=>"Test", "customer_benefits"=>"Test", "financials"=>"£500,000 - £999,999 "}, "n
ew_exception_pm"=>"Test", "new_client"=>"Test", "new_business_div"=>"Test", "new_project_owner"=>"Test", "new_role"=>"Te
st", "new_industry"=>"Test", "commit"=>"Save New Project"}

With 1 technols_id

Started POST "/projects" for 192.168.16.127 at 2012-11-26 16:47:27 +0000
Processing by ProjectsController#create as HTML
  Parameters: {"utf8"=>"Ô£ô", "authenticity_token"=>"8Hgc1GXqNhWkzO3Wgkfpf6z+fdImf6QvAv0XLbP0a5g=", "project"=>{"project
_name"=>"Test", "archive"=>"0", "username"=>"Test", "status"=>"Active", "exception_pm"=>"", "client"=>"", "business_d
iv"=>"", "project_owner"=>"", "start_date"=>"11-12-2012", "first_name"=>"Test", "last_name"=>"McLaughlin", "fullname"=>
"Test Test", "entry_date"=>"2012-11-26", "end_date"=>"20-12-2012", "technol_ids"=>["1"], "techinfo"=>"Test", "rol
e"=>"", "industry"=>"", "summary"=>"Test", "lessons_learned"=>"Test", "customer_benefits"=>"Test", "financials"=>"£250,
000 - £499,999 "}, "new_exception_pm"=>"Test", "new_client"=>"Test", "new_business_div"=>"Test", "new_project_owner"=>"
Test", "new_role"=>"Test", "new_industry"=>"Test", "commit"=>"Save New Project"}

Answer 1

First of all, the name of the field should be used to get the parameters, use like my example. You are receiving an array of tech ids, right? So instead of using if to check nil, use this:

 params[:project][:technol_ids] ||= [18]

It will turn this parameter into array if it is nil.

params[:project][:technol_ids].each do |tech_id|
   @project_technol = @project.projecttechnols.build(:technol_id => tech)
end