belongs_to has_one structure

Question

I have an application which has the following characteristics

There are Clubs
Each Club has Teams
Each Team has Players

I have a users table. The user table basically contains the username and password for the club manager, team manager and the player to login to the system.

How should I structure the models and the tables?

I plan to create tables for Club, Team and Players. But I am not sure show to structure the relationship between them and the users table.

I could create user_id in each of the model, but the relationship would be Club belongs_to User which doesn't seems right. Moreover I would end up with a User model that has the following

has_one :club
has_one :team
has_one :player

Which is not right. A user will have only one of them at any given time.

Is there a better way to structure this?

Answer 1

Under Rails, has_one is really "has at most one". It's perfectly valid to have all three has_one decorators in User. If you want to ensure they only have precisely one, you could add a validation, for instance:

class User < ActiveRecord::Base
  has_one :club
  has_one :team
  has_one :player

  validate :has_only_one

  private

  def has_only_one
    if [club, team, player].compact.length != 1
      errors.add_to_base("Must have precisely one of club, team or player")
    end
  end
end

Since you have the ability to change the users table in the database, I think I would put club_id, team_id, player_id in users, and have the following:

class Club < ActiveRecord::Base
  has_one :user
  has_many :teams
  has_many :players, :through => :teams
end

class Team < ActiveRecord::Base
  has_one :user
  belongs_to :club
  has_many :players
end

class Player < ActiveRecord::Base
  has_one :user
  belongs_to :team
  has_one :club, :through => :team
end

class User < ActiveRecord::Base
  belongs_to :club
  belongs_to :team
  belongs_to :player

  validate :belongs_to_only_one

  def belongs_to_only_one
    if [club, team, player].compact.length != 1
      errors.add_to_base("Must belong to precisely one of club, team or player")
    end
  end
end

I'd even be tempted to rename User as Manager, or have has_one :manager, :class_name => "User" in the Club, Team and Player models, but your call.