Product orders between 2 users

Question

I have three models: User, Product, Offer and a problem with the relationship between these models.

Scenario:

User 1 posts a product

Answer 1

How about

class User < ActiveRecord::Base
  has_many :products  # All products posted by this user
  has_many :offers    # All offers created by this user
end

class Product < ActiveRecord::Base
  belongs_to :user   # This is the user who posts the product (User 1)
  has_many :offers
end

class Offer < ActiveRecord::Base
  belongs_to :product
  belongs_to :user   # This is the user who creates the offer (User 2)

  # Use a 'state' field with values 'nil', 'accepted', 'rejected' 
end 

For your scenario:

# User 1 posts a product
product = user1.products.create

# User 2 can send User 1 an offer with an price e.g $ 10
offer = user2.offers.create(:product => product)

# User 1 can accept or reject the offer
offer.state = 'rejected'

You could refine this depending on your needs - e.g. if the same product could be posted by different users.