1 files changed, 61 insertions, 0 deletions
diff --git a/activerecord/test/cases/habtm_destroy_order_test.rb b/activerecord/test/cases/habtm_destroy_order_test.rb
new file mode 100644
index 0000000000..9dbd339fe7
--- /dev/null
+++ b/activerecord/test/cases/habtm_destroy_order_test.rb
@@ -0,0 +1,61 @@
+# 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