Enclose naked add calls within UoW

Ordinarialy, `add` method is called from within Command or Event handler
methods. When `add` is invoked by itself, like in independent scripts,
we need to ensure all ops in the `add` method are enclosed within a UoW.

src/protean/core/repository.py

@@ -6,8 +6,10 @@
 
 from protean.container import Element, OptionsMixin
 from protean.core.aggregate import BaseAggregate
+from protean.core.unit_of_work import UnitOfWork
 from protean.exceptions import IncorrectUsageError, NotSupportedError
 from protean.fields import HasMany, HasOne
+from protean.globals import current_uow
 from protean.port.dao import BaseDAO
 from protean.port.provider import BaseProvider
 from protean.reflection import association_fields, has_association_fields
@@ -112,6 +114,14 @@ def add(self, aggregate: BaseAggregate) -> BaseAggregate:  # noqa: C901
         transaction in progress, changes are committed immediately to the persistence store. This mechanism
         is part of the DAO's design, and is automatically used wherever one tries to persist data.
         """
+        # `add` is typically invoked in handler methods in Command Handlers and Event Handlers, which are
+        #   enclosed in a UoW automatically. Therefore, if there is a UoW in progress, we can assume
+        #   that it is the active session. If not, we will start a new UoW and commit it after the operation
+        #   is complete.
+        own_current_uow = None
+        if not (current_uow and current_uow.in_progress):
+            own_current_uow = UnitOfWork()
+            own_current_uow.start()
 
         # If there are HasMany/HasOne fields in the aggregate, sync child objects added/removed,
         if has_association_fields(aggregate):
@@ -123,6 +133,10 @@ def add(self, aggregate: BaseAggregate) -> BaseAggregate:  # noqa: C901
         ):
             self._dao.save(aggregate)
 
+        # If we started a UnitOfWork, commit it now
+        if own_current_uow:
+            own_current_uow.commit()
+
         return aggregate
 
     def _sync_children(self, entity):

tests/event_handler/test_uow_around_event_handlers.py

@@ -27,7 +27,7 @@ def send_email_notification(self, event: Registered) -> None:
 @mock.patch("protean.utils.mixins.UnitOfWork.__enter__")
 @mock.patch("tests.event_handler.test_uow_around_event_handlers.dummy")
 @mock.patch("protean.utils.mixins.UnitOfWork.__exit__")
-def test_that_method_is_enclosed_in_uow(mock_exit, mock_dummy, mock_enter, test_domain):
+def test_that_method_is_enclosed_in_uow(mock_exit, mock_dummy, mock_enter):
     mock_parent = mock.Mock()
 
     mock_parent.attach_mock(mock_enter, "m1")

tests/repository/test_add_uow.py

@@ -0,0 +1,25 @@
+import mock
+
+from .elements import Person
+
+
+@mock.patch("protean.core.repository.UnitOfWork.start")
+@mock.patch("protean.core.repository.UnitOfWork.commit")
+def test_that_method_is_enclosed_in_uow(mock_commit, mock_start, test_domain):
+    mock_parent = mock.Mock()
+
+    mock_parent.attach_mock(mock_start, "m1")
+    mock_parent.attach_mock(mock_commit, "m2")
+
+    test_domain.register(Person)
+    test_domain.init(traverse=False)
+    with test_domain.domain_context():
+        person = Person(first_name="John", last_name="Doe", age=29)
+        test_domain.repository_for(Person).add(person)
+
+    mock_parent.assert_has_calls(
+        [
+            mock.call.m1(),
+            mock.call.m2(),
+        ]
+    )