Sync transaction state when accessing primary key

If a record is modified inside a transaction, it must check the outcome
of that transaction before accessing any state which would no longer be
valid if it was rolled back.

For example, consider a new record that was saved inside a transaction
which was later rolled back: it should be restored to its previous state
so that saving it again inserts a new row into the database instead of
trying to update a row that no longer exists.

The `id` and `id=` methods defined on the PrimaryKey module implement
this correctly, but when a model uses a custom primary key, the reader
and writer methods for that attribute must check the transaction state
too. The `read_attribute` and `write_attribute` methods also need to
check the transaction state when accessing the primary key.

1 files changed, 49 insertions, 3 deletions

diff --git a/activerecord/test/cases/transactions_test.rb b/activerecord/test/cases/transactions_test.rb
index 76a997ba8b..a5348e2825 100644
--- a/activerecord/test/cases/transactions_test.rb
+++ b/activerecord/test/cases/transactions_test.rb
@@ -684,7 +684,7 @@ class TransactionTest < ActiveRecord::TestCase
       raise ActiveRecord::Rollback
     end
 
-    assert_nil movie.id
+    assert_nil movie.movieid
   end
 
   def test_assign_id_after_rollback
@@ -707,8 +707,54 @@ class TransactionTest < ActiveRecord::TestCase
       raise ActiveRecord::Rollback
     end
 
-    movie.id = nil
-    assert_nil movie.id
+    movie.movieid = nil
+    assert_nil movie.movieid
+  end
+
+  def test_read_attribute_after_rollback
+    topic = Topic.new
+
+    Topic.transaction do
+      topic.save!
+      raise ActiveRecord::Rollback
+    end
+
+    assert_nil topic.read_attribute(:id)
+  end
+
+  def test_read_attribute_with_custom_primary_key_after_rollback
+    movie = Movie.new(name: "foo")
+
+    Movie.transaction do
+      movie.save!
+      raise ActiveRecord::Rollback
+    end
+
+    assert_nil movie.read_attribute(:movieid)
+  end
+
+  def test_write_attribute_after_rollback
+    topic = Topic.create!
+
+    Topic.transaction do
+      topic.save!
+      raise ActiveRecord::Rollback
+    end
+
+    topic.write_attribute(:id, nil)
+    assert_nil topic.id
+  end
+
+  def test_write_attribute_with_custom_primary_key_after_rollback
+    movie = Movie.create!(name: "foo")
+
+    Movie.transaction do
+      movie.save!
+      raise ActiveRecord::Rollback
+    end
+
+    movie.write_attribute(:movieid, nil)
+    assert_nil movie.movieid
   end
 
   def test_rollback_of_frozen_records