form for - Ruby On Rails, form_for specify one attribute on my own -

i have following form_for - structure

  <%= form_for group.new, url: what_to_do_files_path ,method: :get ,:validate => true |f| %>    <div class="field">   <%=f.text_field :group_name, placeholder: "group name" %>   </div>    <%= button_tag :class => "btn btn-primary", :name => 'submit' %> submit <% end %>   <button type="button" id="check_all"> check / uncheck all</button>    lalalala    <%end%> 

model:

class arraygroup < activerecord::base   attr_accessible :group_name, :user_id       no_whitespace=/^[\s]+$/     validates :group_name,                            :format => { :with => no_whitespace} ,                               :uniqueness => { :scope=> :user_id,:case_sensitive => false}     validates_length_of :group_name, :minimum => 3  end 

so, want able client-side-validate database group_name , user_id.

the problem user can specify name of group in text field , user_id 0 then. want specify user_id on own somehow, example <% f.user_id => @user_spec_id%>, @user_spec_id predefined , points id of user. version doesnt work of course. have tried <% user_id => @user_spec_id%> wrong.

thanks in advance

you looking hidden_field_tag

in view, following,

<%= hidden_field_tag #{f.object_name}[user_id], @user_spec_id %> 

obviously inside form_for.

when submit form, see that, in params["group"] hash, added user_id.