Puppy model and Charge model

puppy.rb

## user.rb
class User < ActiveRecord::Base
  ....
  has_many :puppies, dependent: :destroy
  has_many :paid_charges, class_name: 'Charge',
  foreign_key: 'user_id', dependent: :destroy
  has_many :received_charges, class_name: 'Charge',
  foreign_key: 'vendor_id', dependent: :destroy
end
## puppy.rb
class Puppy < ActiveRecord::Base
  belongs_to :user
end
## charge.rb
class Charge < ActiveRecord::Base
  belongs_to :user
  belongs_to :vendor, class_name: 'User', foreign_key: 'vendor_id'
end