You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: delete_dispensed_exams_and_frequencies_service.rb
    path of file: ./repos/i-diario/app/services
    
    the code of the file until where you have to start completion: class DeleteDispensedExamsAndFrequenciesService
  def initialize(student_enrollment_id, discipline_id, steps)
    @student_enrollment_id = student_enrollment_id
    @discipline_id = discipline_id
    @steps = steps
  end

  def 
    
  def destroy_invalid_descriptive_exams(student_id, classroom_id, step_number)
    descriptive_exam_ids = DescriptiveExam.by_discipline_id(@discipline_id)
                                          .by_classroom_id(classroom_id)
                                          .by_step_number(step_number)
                                          .pluck(:id)

    DescriptiveExamStudent.by_student_id(student_id)
                          .by_descriptive_exam_id(descriptive_exam_ids)
                          .destroy_all
  end