From 4576a407e0cf16b92e18f1a3654d0c2f190e36c6 Mon Sep 17 00:00:00 2001
From: Kyle Sferrazza <kyle.sferrazza@gmail.com>
Date: Fri, 8 Oct 2021 07:02:01 -0400
Subject: [PATCH 1/3] registrations are unique for examversion,user pairs

---
 app/models/registration.rb | 2 ++
 test/models/user_test.rb   | 8 ++++++++
 2 files changed, 10 insertions(+)

diff --git a/app/models/registration.rb b/app/models/registration.rb
index 3ede8051b..30c9d0df8 100644
--- a/app/models/registration.rb
+++ b/app/models/registration.rb
@@ -24,6 +24,8 @@ class Registration < ApplicationRecord
   delegate :course, to: :exam
   delegate :term, to: :course
 
+  validates :user, uniqueness: { scope: :exam_version }
+
   def room_version_same_exam
     return unless room
 
diff --git a/test/models/user_test.rb b/test/models/user_test.rb
index 83cbe5453..05ea8df11 100644
--- a/test/models/user_test.rb
+++ b/test/models/user_test.rb
@@ -10,4 +10,12 @@ class UserTest < ActiveSupport::TestCase
   test 'admin factory builds admins' do
     assert build(:admin).admin?
   end
+
+  test 'cannot create two registrations for the same ExamVersion-User pair' do
+    r1 = create(:registration)
+    r2 = build(:registration, user: r1.user, exam_version: r1.exam_version)
+    assert_not r2.valid?
+    assert_match(/has already been taken/, r2.errors.full_messages.to_sentence)
+    assert_not r2.save
+  end
 end

From e7bd0cab5f5cc8c3c0b33074f946a85e1ba378ce Mon Sep 17 00:00:00 2001
From: Kyle Sferrazza <kyle.sferrazza@gmail.com>
Date: Fri, 8 Oct 2021 07:54:25 -0400
Subject: [PATCH 2/3] registrations are unique for exam,user pairs

---
 app/models/registration.rb | 11 +++++++++++
 test/models/user_test.rb   |  9 +++++++++
 2 files changed, 20 insertions(+)

diff --git a/app/models/registration.rb b/app/models/registration.rb
index 30c9d0df8..e7c882f8f 100644
--- a/app/models/registration.rb
+++ b/app/models/registration.rb
@@ -26,6 +26,17 @@ class Registration < ApplicationRecord
 
   validates :user, uniqueness: { scope: :exam_version }
 
+  validate :user_exam_uniqueness
+  def user_exam_uniqueness
+    other_reg_exists =
+      user
+      .registrations
+      .where(exam_version: exam.exam_versions)
+      .where.not(exam_version: exam_version)
+      .any?
+    errors.add(:user, 'already has a registration for another version of that exam') if other_reg_exists
+  end
+
   def room_version_same_exam
     return unless room
 
diff --git a/test/models/user_test.rb b/test/models/user_test.rb
index 05ea8df11..8421daa6e 100644
--- a/test/models/user_test.rb
+++ b/test/models/user_test.rb
@@ -18,4 +18,13 @@ class UserTest < ActiveSupport::TestCase
     assert_match(/has already been taken/, r2.errors.full_messages.to_sentence)
     assert_not r2.save
   end
+
+  test 'cannot create two registrations for the same Exam-User pair' do
+    r1 = create(:registration)
+    second_version = create(:exam_version, exam: r1.exam)
+    r2 = build(:registration, user: r1.user, exam_version: second_version)
+    assert_not r2.valid?
+    assert_match(/has a registration for another version/, r2.errors.full_messages.to_sentence)
+    assert_not r2.save
+  end
 end

From d0c7b429816bea5430e041dcfbfd702660bf196e Mon Sep 17 00:00:00 2001
From: Kyle Sferrazza <6677292+kylesferrazza@users.noreply.github.com>
Date: Fri, 8 Oct 2021 13:09:36 -0400
Subject: [PATCH 3/3] Add note to uniqueness checks in registration

---
 app/models/registration.rb | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/app/models/registration.rb b/app/models/registration.rb
index e7c882f8f..6f6d2d310 100644
--- a/app/models/registration.rb
+++ b/app/models/registration.rb
@@ -26,6 +26,8 @@ class Registration < ApplicationRecord
 
   validates :user, uniqueness: { scope: :exam_version }
 
+  # note: we are not sure whether the current reg will show up in the association,
+  # so this validation remains separate from the previous uniqueness check
   validate :user_exam_uniqueness
   def user_exam_uniqueness
     other_reg_exists =