started implementing teams

app/models/exercise.rb

@@ -7,6 +7,7 @@ class Exercise < ActiveRecord::Base
 
   belongs_to :execution_environment
   has_many :submissions
+  belongs_to :team
   has_many :users, source_type: ExternalUser, through: :submissions
 
   scope :with_submissions, -> { where('id IN (SELECT exercise_id FROM submissions)') }

app/models/internal_user.rb

@@ -3,6 +3,8 @@ class InternalUser < ActiveRecord::Base
 
   authenticates_with_sorcery!
 
+  has_and_belongs_to_many :teams
+
   validates :email, presence: true, uniqueness: true
   validates :password, confirmation: true, on: :update, presence: true, unless: :activated?
   validates :role, inclusion: {in: ROLES}

app/models/team.rb

@@ -0,0 +1,10 @@
+class Team < ActiveRecord::Base
+  has_and_belongs_to_many :internal_users
+  alias_method :members, :internal_users
+
+  validates :name, presence: true
+
+  def to_s
+    name
+  end
+end