has_many through form and adding attribute to join table - ruby-on-rails

Question

This is my first stakoverflow question and fairly new to Rails. I've searched through previous similar questions but can't seem to figure this one out. I have a has_many through relationship with Users and Accounts and I have an extra boolean attribute "account_admin" on the UserAccount model (join table). I'm trying to figure out how to set this when I create a new Account.
User:
class User < ActiveRecord::Base
has_many :user_accounts, :dependent => :destroy
has_many :accounts, :through => :user_accounts
..
end
Account:
class Account < ActiveRecord::Base
has_many :user_accounts, :dependent => :destroy
has_many :users, :through => :user_accounts
end
UserAccount:
class UserAccount < ActiveRecord::Base
belongs_to :user
belongs_to :account
# includes account_admin boolean
end
I would like to be able to create an account, assign users to that account, and designate an account_admin all in one form. I have this so far which allows me to select the users in an account but I'm not sure how to set the account_admin boolean here as well.
= simple_form_for #account do |f|
= f.input :name
= f.input :description
= f.association :users, label_method: :to_label, :as => :check_boxes
= f.button :submit
Appreciate any tips. Thanks

Answer 1

Account model:
class Account < ActiveRecord::Base
attr_accessible :name, :description, :user_accounts_attributes
has_many :user_accounts, :dependent => :destroy
has_many :users, :through => :user_accounts
has_many :user_without_accounts, :class_name => 'User', :finder_sql => Proc.new {
%Q{
SELECT *
FROM users where id NOT IN (Select user_id from user_accounts where account_id = #{id})
}
}
accepts_nested_attributes_for :user_accounts, reject_if: proc { |attributes| attributes['user_id'] == '0' }
def without_accounts
new_record? ? User.all : user_without_accounts
end
end
In form:
= simple_form_for #account do |f|
= f.input :name
= f.input :description
- #account.user_accounts.each do |user_account|
= f.simple_fields_for :user_accounts, user_account do |assignment|
= assignment.check_box :user_id
= assignment.label :user_id, user_account.user.name rescue raise user_account.inspect
= assignment.input :account_admin
%hr
- #account.without_accounts.each do |user|
= f.simple_fields_for :user_accounts, #account.user_accounts.build do |assignment|
= assignment.check_box :user_id
= assignment.label :user_id, user.name
= assignment.input :account_admin
%hr
= f.button :submit