Rails: Access params of a form with a nested model

I have the following models

class GymUser < ActiveRecord::Base
  belongs_to :user 
  belongs_to :gym 
end

class User < ActiveRecord::Base
  has_many :gym_users
  has_one :gym

  attr_accessible :gym_users_attributes, :gym_users
  accepts_nested_attributes_for :gym_users
end

I have a form for a new user, with a nested model gym_user. I want to make sure the user doesn't exist already. This is what I'm trying:

def create_member
  @user = User.new(params[:user])
  @user.generate_password
  @dupe = User.find_all_by_email(@user.email)
  if(@dupe)
    @gym_user = GymUser.new(params[:user][:gym_users_attributes])
    @gym_user.user_id = @dupe.id
  elsif @user.save
    @gym_user = @user.gym_users.order('created_at DESC').first
    @gym = Gym.find(@gym_user.gym_id)
  end
end

I know there's only one nested model here, but I can't figure out how to access those nested parameters.

Here's the form itself

<%= form_for @user, :as => :user, :remote => true, :url => { :controller => 'users', :action => 'create_member'} do |f| %>
    <table border="0" cellpadding="10" cellspacing="0">
        <tr>
            <td colspan="2">
                <%= f.label :name %><br />
                <%= f.text_field :name %>
            </td>
            <td colspan="2">
                <%= f.label :email %><br />
                <%= f.text_field :email %>
            </td>
        </tr>
        <% f.fields_for :gym_users do |builder| %>
            <tr>
                <td>
                    <%= builder.label :role_id, "Role" %><br />
                    <%= builder.collection_select(:role_id, @roles, :id, :name, {:include_blank => true}, {:onchange => "new_member_role_changed()"}) %>
                    <%= builder.hidden_field :gym_id, :value => @gym.id %>
                </td>
                <td>
                    <%= builder.label :item_id, "Membership Level" %><br />
                    <%= builder.collection_select(:item_id, @gym.membership_items, :id, :name, {:include_blank => true}) %>
                </td>
                <td>
                    <%= builder.label :has_monthly_billing, "Recurring Billing?" %><br />
                    <%= builder.radio_button :has_monthly_billing, "1" %>Yes &nbsp;
                    <%= builder.radio_button :has_monthly_billing, "0" %>No
                </td>
                <td>
                    <%= builder.label :billing_date %><br />
                    <%= builder.collection_select(:billing_date, (1..31).to_a, :to_s, :to_s, {:include_blank => true}) %>
            开发者_运维问答    </td>
            </tr>
            <tr>
                <td colspan="4">
                    <%= f.submit %>
                    <a href="javascript:close_new_member()">Cancel</a>
                </td>
            </tr>
        <% end %>
    </table>
<% end %>

I found the answer. I'm not sure if this is the best way but it works

params[:user][:gym_users_attributes].values.first

Your association should be

has_one :gym, :through => gym_users

Also, can you post your form paramaters?

Your focus is on not allowing creation of duplicate users, and you are using email to verify this. You should rather use the helper

validates_uniqueness_of :email

in your User model. As you have a nested attribute, your object will be created only after Rails validates that a user with same email doesn't exist already.

I hope I understood your problem right.