git init

app/models/team.example

@@ -0,0 +1,17 @@
+class Team < ActiveRecord::Base
+  attr_accessible :name, :max_members, :private_team
+
+  belongs_to :captain, :class_name => 'User'
+  has_many :team_memberships
+  has_many :members, :through => :team_memberships, :source => :user
+
+  validates :name, :presence => true, :uniqueness => true, :length => { :minimum => 3 }
+  validates :max_members, :presence => true, :numericality => { :only_integer => true, :greater_than => 0 }
+  validates :captain, :presence => true
+
+  self.per_page = 15
+
+  def to_s
+    "#{name}#{private_team? ? '*' : ''}"
+  end
+end

app/models/team_membership.example

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+class TeamMembership < ActiveRecord::Base
+  belongs_to :team
+  belongs_to :user
+
+  validates :user, :presence => true
+  validates :team, :presence => true
+  validates :user_id, :uniqueness => { :scope => :team_id }
+  validate :no_captains_allowed
+
+
+  private
+
+  def no_captains_allowed
+    if user.present? && team.present? && team.captain == user
+      errors.add(:user, "Captain is already a member.")
+    end
+  end
+end

app/models/user.rb

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+class User < ActiveRecord::Base
+  # Include default devise modules. Others available are:
+  # :token_authenticatable, :encryptable, :confirmable, :lockable, :timeoutable and :omniauthable
+  devise :database_authenticatable, :registerable,
+         :recoverable, :rememberable, :trackable, :validatable, :lockable #TODO ,:confirmable
+
+  # Setup accessible (or protected) attributes for your model
+  attr_accessible :email, :password, :password_confirmation, :remember_me,
+    :first_name, :last_name, :nickname
+
+  validates :first_name, :presence => true
+  validates :last_name, :presence => true
+
+  def to_s
+    "#{first_name} #{last_name}"
+  end
+end