Fix create_or_find_by not rolling back a transaction:

- Fix rails#54830 (This indirectly fix the issue)
- ### Problem

  The `create_or_find_by` method doesn't allow rolling back
  a transaction. This is a different behaviour than its counterpart
  method `find_or_create_by`.
  The reason is because we are in the double transaction edge case and
  the outer transaction doesn't see the rollback.

  ### Details

  ```ruby
  class User < ApplicationRecord
    after_save do
      raise ActiveRecord::Rollback
    end
  end

  User.find_or_create_by(name: "John") => Correctly rolled back
  User.create_or_find_by(name: "John") => Does not roll back
  ```

  ### Solution

  We need to be able to know whether the inner transaction succeeded,
  which is not possible using `.create`, as this method always returns
  the record (rather than the status of the transaction).
  https://github.com/rails/rails/blob/1eac7f27748ffa43c5ce91c036c928fc22d4c597/activerecord/lib/active_record/persistence.rb#L39

  Using `new` followed by a save is equivalent to `create`, but
  with `save` we get the transaction return status and we can
  properly rollback the outer transaction.

Author: Edouard-chin

activerecord/lib/active_record/relation.rb

@@ -272,7 +272,12 @@ def find_or_create_by!(attributes, &block)
     # such situation.
     def create_or_find_by(attributes, &block)
       with_connection do |connection|
-        transaction(requires_new: true) { create(attributes, &block) }
+        record = nil
+        transaction(requires_new: true) do
+          record = new(attributes, &block)
+          record.save || raise(ActiveRecord::Rollback)
+        end
+        record
       rescue ActiveRecord::RecordNotUnique
         if connection.transaction_open?
           where(attributes).lock.find_by!(attributes)
@@ -287,7 +292,12 @@ def create_or_find_by(attributes, &block)
     # is raised if the created record is invalid.
     def create_or_find_by!(attributes, &block)
       with_connection do |connection|
-        transaction(requires_new: true) { create!(attributes, &block) }
+        record = nil
+        transaction(requires_new: true) do
+          record = new(attributes, &block)
+          record.save! || raise(ActiveRecord::Rollback)
+        end
+        record
       rescue ActiveRecord::RecordNotUnique
         if connection.transaction_open?
           where(attributes).lock.find_by!(attributes)

activerecord/test/cases/relations_test.rb

@@ -1593,6 +1593,24 @@ def test_create_or_find_by
     assert_not_equal subscriber, Subscriber.create_or_find_by(nick: "cat")
   end
 
+  def test_create_or_find_by_rollbacks_a_transaction
+    assert_no_difference(-> { Car.count }) do
+      car = BrokenCar.create_or_find_by(name: "Civic")
+
+      assert_instance_of(BrokenCar, car)
+      assert_not_predicate(car, :persisted?)
+    end
+  end
+
+  def test_create_or_find_by_bang_rollbacks_a_transaction
+    assert_no_difference(-> { Car.count }) do
+      car = BrokenCar.create_or_find_by!(name: "Civic")
+
+      assert_instance_of(BrokenCar, car)
+      assert_not_predicate(car, :persisted?)
+    end
+  end
+
   def test_create_or_find_by_with_block
     assert_nil Subscriber.find_by(nick: "bob")
 

activerecord/test/models/car.rb

@@ -35,3 +35,9 @@ class CoolCar < Car
 class FastCar < Car
   default_scope { order("name desc") }
 end
+
+class BrokenCar < Car
+  after_save do
+    raise ActiveRecord::Rollback
+  end
+end