Join Table

class CreateProjectUsers < ActiveRecord::Migration
  def change
    create_table :project_users do |t|
      t.integer :user_id
      t.integer :project_id

      t.timestamps
    end
    
    add_index :project_users, [ :user_id, :project_id], unique: true
  end
end

Project Model

class Project < ActiveRecord::Base
  attr_accessible :author_id, :description, :name

  has_and_belongs_to_many :users
end

User Model

class User < ActiveRecord::Base
  # Include default devise modules. Others available are:
  # :token_authenticatable, :confirmable,
  # :lockable, :timeoutable and :omniauthable
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable

  # Setup accessible (or protected) attributes for your model
  attr_accessible :email, :password, :password_confirmation, :remember_me
  # attr_accessible :title, :body

  has_and_belongs_to_many :roles
  has_many :blogPosts

  def role?(role)
    return true 
    # roles.include? role.to_s
  end

  def to_s
    email
  end
end