ActiveRecord - Find next user in group model - ruby-on-rails

Question

I've four user models: Zone, Product, User, Group
I want to choose what Users can sell a Product in a Zone, this is what Group does, with a many to many relation to User and a foreign key to one Product and one Zone. So I have one group per pair Zone/Product. I will also need to set custom attributes on that many to many relation so I used has_many :through Sell (I was unable to find a better name to describe the relation between Group and User).
So I ended up having 5 models: Zone, Product, User, Group, Sell.
It works fine, but now I'd need to select the next user available in a Group.
I was thinking to exploit Sell.id to find the user assigned to the same group with an higher id, if not present choose the first one again (this allows me to create a ring chain).
It would be useful to have a Group.next_user method.
Unfortunatly I can't figure out how to do this, I'd need help to find the next user available in the group (or the 1st one if there are no more users).
Follows the code for models all the models:
################
# models/group.rb
################
class Group < ActiveRecord::Base
has_many :sells
has_many :users, :through => :sells
belongs_to :zone
belongs_to :product
attr_accessible :priority, :product_id, :user_ids, :zone_id
end
################
# models/zone.rb
################
class Zone < ActiveRecord::Base
belongs_to :location
has_many :cities
has_many :groups
attr_accessible :name, :location_id
validates :location, :presence => true
end
################
# models/user.rb
################
class User < ActiveRecord::Base
after_create :create_calendar
before_destroy :destroy_calendar
belongs_to :location
belongs_to :mall
has_one :event_calendar
has_many :sells
has_many :groups, :through => :sells
# Include default devise modules. Others available are:
# :token_authenticatable, :encryptable, :confirmable, :lockable, :timeoutable and :omniauthable, :registerable,
# :recoverable, :rememberable,
devise :database_authenticatable, :trackable,
:validatable, :authentication_keys => [:username]
# Setup accessible (or protected) attributes for your model
attr_accessible :username, :password, :password_confirmation, :remember_me, :name,
:surname, :role, :location_id
# attr_accessible :title, :body
ROLES = %w[Admin Agente Hostess HostessAdmin]
validates_uniqueness_of :username, :case_sensitive => false
validates :username, :presence => true
validates_presence_of :role, :name, :surname, :location_id
validates :location, :presence => true
validates :role, :inclusion => { :in => ROLES, :message => "%{value} non è un ruolo valido." }
def display_name
"#{self.name} #{self.surname}"
end
def has_role?(role)
# convert the role string to a sybmol
self.role.downcase.gsub(/\s+/, "_").to_sym == role
end
private
def create_calendar
if self.has_role? :agente
calendar = EventCalendar.new({:user_id => self.id})
calendar.save()
end
end
def destroy_calendar
if self.has_role? :agente
calendar = EventCalendar.find_by_user_id(self.id)
calendar.destroy()
end
end
def email_required?
false
end
def email_changed?
false
end
end
################
# models/product.rb
################
class Product < ActiveRecord::Base
after_create :create_groups
before_destroy :destroy_groups
attr_accessible :name
def create_groups
for zone in Zone.all
group = Group.new({:zone_id => zone.id, :product_id => self.id})
group.save()
end
end
def destroy_groups
for zone in Zone.all
group = Group.find_by_product_id(self.id)
group.destroy
end
end
end
################
# models/sell.rb
################
class Sell < ActiveRecord::Base
belongs_to :user
belongs_to :group
end
Can you give me some help to get this done? Thanks!

Answer 1

If I get this right then addd this to your User model
scope :next, lambda { |p| {:conditions => ["id > ?", p.id], :limit => 1, :order => "id"} }
and this to your group model
def self.next_user
return User.first if Group.users.blank?
next_user = User.next(Group.users.last).first
return next_user || Group.users.first
end
This should do the trick. I didn't write test for this so you should test it :)