Final has_one code

has_one_final.rb

class Employee
  belongs_to: :department
  has_one :organization, through: :department 
end

class Departmet
  belongs_to :organization
  has_many :project_departments
  has_many :projects, through: :project_departments
  has_many :employees
  has_one :head_of_department, -> { where role: 'department_head' }, class_name: 'Employee'
end

class Organization
  has_many :departments
  has_many :employees through: :departments
end


class Project
  has_many :project_departments
  has_many :departments, through: :project_departments
  has_one :project_department, ->(department) { where department: department }, class_name: 'ProjectDepartment'  
end

class ProjectDepartment
  belongs_to :project
  belongs_to :project
end

"class Departmet" should be "class Department"