http://minus.com/i/Eq1w6akKgYbb
User has_many :memberships, foreign_key :member_id has_many :created_groups has_many :joined_groups, through: :memberships
Group has_many :memberships belongs_to :creator, class_name: "User" has_many :members, through: :memberships
Membership belongs_to :group belongs_to :member, class_name: "User"