То как я все сделал

file.rb

#Вот модель task.rb
class Task < ActiveRecord::Base
	extend FriendlyId
	friendly_id :title, use: [:slugged, :finders]

  has_many :taskstatus
  has_many :users, through: :taskstatus
  
#Вот модель user.rb
class User < ActiveRecord::Base
  # Include default devise modules. Others available are:
  # :confirmable, :lockable, :timeoutable and :omniauthable
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable,
         :omniauthable
         
  validates :name, presence: true, length: {maximum: 25}
  
  has_many :taskstatus
  has_many :tasks, through: :taskstatus
  
#Вот модель Taskstatus
class Taskstatus < ActiveRecord::Base
  belongs_to :user
  belongs_to :task
end