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

Your models are good enough, except for the relations. The confusion starts when you are trying to differentiate the owned products vs interested products(offered) and product owner vs interested users(users who placed the offer). If you can come up with a better naming convention, you can easily fix it.

1. Better relations

class User < ActiveRecord::Base
  attr_accessible :name, :email, :password, :password_confirmation, :remember_me, :avatar, :screen_name
  has_many :owned_products, :class_name => "Product"
  has_many :offers 
  has_many :interested_products, :through => :offers
end

class Offer < ActiveRecord::Base
  attr_accessible :offer_price, :status, :user_id, :product_id
  belongs_to :interested_user, :class_name => "User", :foreign_key => :user_id
  belongs_to :interested_product, :class_name => "Product", :foreign_key => :product_id
end

class Product < ActiveRecord::Base
  attr_accessible :content, :price, :title, :tag_list, :productimage, :user_id
  belongs_to :owner, :foreign_key => :user_id, :class_name => "User"
  has_many :offers 
  has_many :interested_users, :through => :offers
end

With these relations I think you can get all the basic information you would be interested. For Example,

@product = Product.find(1)
@product.owner # would give you the user who created the product
@product.interested_users # would give you users who placed an offer for this product

@user = User.find(1)
@user.owned_products # would give you the products created by this user
@user.interested_products # would give you the products where the user placed an offer

2. Handling accept and reject actions.

From your description, I see there can be 2 possible state changes to an offer, "created" -> "accept" or "created" -> "reject". I suggest you to look at state_machine. State machine will add nice flavor to your model with its helper methods, which I think will be very useful in your case. So your Offer model will look something like this,

class Offer < ActiveRecord::Base
  # attr_accessible :title, :body
  attr_accessible :offer_price, :status, :user_id, :product_id
  belongs_to :interested_user, :class_name => "User", :foreign_key => :user_id
  belongs_to :interested_product, :class_name => "Product", :foreign_key => :product_id

  state_machine :status, :initial => :created do
    event :accept do
      transition :created => :accepted
    end
    event :reject do
      transition :created => :reject
    end
  end
end

#cool helper methods
@offer = Offer.new
@offer.accepted? #returns false
@offer.reject #rejects the offer
@offer.rejected? #returns true

I hope this gives you a better picture.