ruby on rails - Using form_for with "becomes" loses child association -

when building out form handles sti, if use becomes transform object parent class, lose ability use nested fields it.

i have 2 models

class login < activerecord::base   belongs_to :user end  class user < activerecord::base   has_one :login    accepts_nested_attributes_for :login end 

i have few subclasses of user.

class consumer < user end  class admin < user end  class agent < user end 

initially had problems routing, since rails assume wanted route specific current class rather parent class, used @user.becomes(user), apparently way handle that. part works fine, causes @user.login disappear.

controller

class admin::userscontroller < admincontroller   load_and_authorize_resource   before_filter :authenticate_user!    def index     render 'index'   end    def new     @user = user.new     @user.build_login     render 'new'   end    def create     @user = user.new(user_params)      if @user.save       flash[:notice] = "account confirmation instructions sent #{@user.login.email}"       redirect_to new_user_path     else       flash.now[:error] = @user.errors.full_messages.to_sentence       # @ point, can confirm @user.login still exists...       render 'new'     end   end    private     def user_params       params.require(:user).permit(         :type,         :dealership_id,         login_attributes: [           :email         ])     end  end 

here's relevant form view bit

<%= simple_form_for(@user.becomes(user), html: {class: "user-form"}) |f| %>    <%= f.simple_fields_for :login |l| %>     <div class="field">       <%= l.label :email %><br />       <%= l.email_field :email %>     </div>   <% end %>    <div class="field">     <%= f.label :type %>     <%= f.select :type, options_for_select(current_user.types_can_create), include_blank: "- select -", class: "form-control", id: "select_type" %>   </div>    <div class="actions">     <%= f.submit "register" %>   </div> <% end %> 

the text field :email doesn't display because @user.login nil. expected behavior when using becomes?

having used becomes once before, can attest scant experience -- whenever use it, invokes new instance of class.

i'm not sure specifics, bottom line surmise @user.becomes(user) overriding @user.build_login...

returns instance of specified klass attributes of current record.

--

in case, set path explicitly (as you're using user anyway):

<%= simple_form_for @user, url: user_path, method: :post html: {class: "user-form"} |f| %>