activerecord/test/cases/habtm_destroy_order_test.rb


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# frozen_string_literal: true

require "cases/helper"
require "models/lesson"
require "models/student"

class HabtmDestroyOrderTest < ActiveRecord::TestCase
  test "may not delete a lesson with students" do
    sicp = Lesson.new(name: "SICP")
    ben = Student.new(name: "Ben Bitdiddle")
    sicp.students << ben
    sicp.save!
    assert_raises LessonError do
      assert_no_difference("Lesson.count") do
        sicp.destroy
      end
    end
    assert_not_predicate sicp, :destroyed?
  end

  test "should not raise error if have foreign key in the join table" do
    student = Student.new(name: "Ben Bitdiddle")
    lesson = Lesson.new(name: "SICP")
    lesson.students << student
    lesson.save!
    assert_nothing_raised do
      student.destroy
    end
  end

  test "not destroying a student with lessons leaves student<=>lesson association intact" do
    # test a normal before_destroy doesn't destroy the habtm joins
    sicp = Lesson.new(name: "SICP")
    ben = Student.new(name: "Ben Bitdiddle")
    # add a before destroy to student
    Student.class_eval do
      before_destroy do
        raise ActiveRecord::Rollback unless lessons.empty?
      end
    end
    ben.lessons << sicp
    ben.save!
    ben.destroy
    assert_not_empty ben.reload.lessons
  ensure
    # get rid of it so Student is still like it was
    Student.reset_callbacks(:destroy)
  end

  test "not destroying a lesson with students leaves student<=>lesson association intact" do
    # test a more aggressive before_destroy  doesn't destroy the habtm joins and still throws the exception
    sicp = Lesson.new(name: "SICP")
    ben = Student.new(name: "Ben Bitdiddle")
    sicp.students << ben
    sicp.save!
    assert_raises LessonError do
      sicp.destroy
    end
    assert_not_empty sicp.reload.students
  end
end