When two models (Project, Employee) belong to a parent (Company) and are joined through a join model (ProjectEmployee), what's the best way to ensure that the two instances being joined belong to the same parent? Ex: how do you ensure the joined project and employee belong to the same company?

validate_join_model.rb

class Company < ApplicationRecord
  has_many :employees
  has_many :projects
end


class Project < ApplicationRecord
  belongs_to :company

  has_many :project_employees
  has_many :employees, through: :project_employees
end


class Employee < ApplicationRecord
  belongs_to :company

  has_many :project_employees
  has_many :projects, through: :project_employees
end


class ProjectEmployee < ApplicationRecord
  belongs_to :project
  belongs_to :employee

  # There has to be a better way! 👇

  validate :project_and_employee_belong_to_same_company

  def project_and_employee_belong_to_same_company
    if project.company != employee.company
      errors.add(:base, 'Project and employee do not belong to same company.')
    end
  end
end