action update only last object - ruby-on-rails

Question

From last two days i try expect whats going on in my app. This is my problem:
My model:
class User
has_many :orders
---
class Order
belongs_to :user
has_and_belongs_to_many :contributors, class_name: 'User'
Situation:
User can create order, next for this order can add contributors(other users) with
<%= collection_check_boxes(:order, :contributor_ids, #prac, :id, :to_s) %>
After that in my custom action in OrdersController i have something like this:
#order.contributors.each do |u|
u.orders << #order
end
Here i want add this order to list of contributors(users) orders. Unfortunately this work only for last contributor(user). Below log from my console:
Started PATCH "/orders/282/zatwierdz" for 127.0.0.1 at 2014-07-01 08:48:59 +0200
Processing by OrdersController#zatwierdz as HTML
Parameters: {"authenticity_token"=>"hxWUnazKLoS9t8bVmOAMeIxdo/KYuO33bUeuQZYgeV
k=", "id"=>"282"}
User Load (0.0ms) SELECT "users".* FROM "users" WHERE "users"."id" = 32 OR
DER BY "users"."id" ASC LIMIT 1
Role Load (0.0ms) SELECT "roles".* FROM "roles" WHERE "roles"."id" = ? LIMI
T 1 [["id", 4]]
Order Load (0.0ms) SELECT "orders".* FROM "orders" WHERE "orders"."id" = ?
ORDER BY created_at DESC LIMIT 1 [["id", 282]]
OrderItem Exists (0.0ms) SELECT 1 AS one FROM "order_items" WHERE "order_it
ems"."order_id" = ? LIMIT 1 [["order_id", 282]]
(0.0ms) begin transaction
SQL (0.0ms) UPDATE "orders" SET "status" = ?, "updated_at" = ? WHERE "orders"
."id" = 282 [["status", 1], ["updated_at", "2014-07-01 06:48:59.486472"]]
(62.5ms) commit transaction
User Load (0.0ms) SELECT "users".* FROM "users" INNER JOIN "orders_users" ON
"users"."id" = "orders_users"."user_id" WHERE "orders_users"."order_id" = ? [["
order_id", 282]]
(0.0ms) begin transaction
(0.0ms) commit transaction
(0.0ms) begin transaction
SQL (0.0ms) UPDATE "orders" SET "updated_at" = ?, "user_id" = ? WHERE "orders
"."id" = 282 [["updated_at", "2014-07-01 06:48:59.564595"], ["user_id", 33]]
(78.1ms) commit transaction
(0.0ms) begin transaction
SQL (0.0ms) UPDATE "orders" SET "updated_at" = ?, "user_id" = ? WHERE "orders
"."id" = 282 [["updated_at", "2014-07-01 06:48:59.642719"], ["user_id", 35]]
(78.1ms) commit transaction
(0.0ms) begin transaction
SQL (0.0ms) UPDATE "orders" SET "updated_at" = ?, "user_id" = ? WHERE "orders
"."id" = 282 [["updated_at", "2014-07-01 06:48:59.720842"], ["user_id", 36]]
(109.4ms) commit transaction
(0.0ms) begin transaction
SQL (0.0ms) UPDATE "orders" SET "updated_at" = ?, "user_id" = ? WHERE "orders
"."id" = 282 [["updated_at", "2014-07-01 06:48:59.830215"], ["user_id", 37]]
(78.1ms) commit transaction
Redirected to http://localhost:3000/orders/282
Completed 302 Found in 437ms (ActiveRecord: 406.2ms)
I try use this action with callbacks and from model methods but nothing happened. Maybe better for this aprouch is to use other associations? Anny sugestions welcome.
Thx for help.

Answer 1

By doing:
#order.contributors.each do |u|
u.orders << #order
end
You are adding your order to the user.orders relationship, which you define as a many (Order) to one (User). The "has_many" orders on the User class is just the other side of the "belongs_to" user on the Order class. So yes, as per your model, an Order has one and only one user.
Now, if you want to be able to navigate your has_and_belongs_to_many relation from the User side, you need to define it there too.