Adding @nested_transactional for transactions that require more than one

db update/insert.

Using a savepoint for the multiple transactions allows us to rollback if
there is an error when executing the second db transaction.
However, this does add a bit of complexity. Developers need to manage
the db session when calling multiple nested tranactions.

Unit tests have been added to test this functionality and some end to
end tests have been done to make sure all transactions are rollback if
there is an exception while executing the transaction.

tests/app/organisation/test_rest.py

@@ -505,14 +505,54 @@ def test_post_link_service_to_organisation(admin_request, sample_service):
         organisation_id=organisation.id,
         _expected_status=204
     )
-
     assert len(organisation.services) == 1
     assert sample_service.organisation_type == 'central'
+
+
+def test_post_link_service_to_organisation_inserts_annual_billing(admin_request, sample_service):
+    data = {
+        'service_id': str(sample_service.id)
+    }
+    organisation = create_organisation(organisation_type='central')
+    assert len(organisation.services) == 0
+    assert len(AnnualBilling.query.all()) == 0
+    admin_request.post(
+        'organisation.link_service_to_organisation',
+        _data=data,
+        organisation_id=organisation.id,
+        _expected_status=204
+    )
+
     annual_billing = AnnualBilling.query.all()
     assert len(annual_billing) == 1
     assert annual_billing[0].free_sms_fragment_limit == 150000
 
 
+def test_post_link_service_to_organisation_rollback_service_if_annual_billing_update_fails(
+        admin_request, sample_service, mocker
+):
+    mocker.patch('app.dao.annual_billing_dao.dao_create_or_update_annual_billing_for_year',
+                 side_effect=SQLAlchemyError)
+    data = {
+        'service_id': str(sample_service.id)
+    }
+    assert not sample_service.organisation_type
+
+    organisation = create_organisation(organisation_type='central')
+    assert len(organisation.services) == 0
+    assert len(AnnualBilling.query.all()) == 0
+    with pytest.raises(expected_exception=SQLAlchemyError):
+        admin_request.post(
+                'organisation.link_service_to_organisation',
+                _data=data,
+                organisation_id=organisation.id,
+                _expected_status=404
+            )
+    assert not sample_service.organisation_type
+    assert len(organisation.services) == 0
+    assert len(AnnualBilling.query.all()) == 0
+
+
 def test_post_link_service_to_another_org(
         admin_request, sample_service, sample_organisation):
     data = {
@@ -582,23 +622,6 @@ def test_post_link_service_to_organisation_missing_payload(
     )
 
 
-def test_link_service_to_organisation_updates_service_if_annual_billing_update_fails(
-        mocker, admin_request, sample_service, sample_organisation
-):
-    mocker.patch('app.organisation.rest.set_default_free_allowance_for_service', raises=SQLAlchemyError)
-    data = {
-        'service_id': str(sample_service.id)
-    }
-    admin_request.post(
-        'organisation.link_service_to_organisation',
-        organisation_id=str(sample_organisation.id),
-        _data=data,
-        _expected_status=204
-    )
-    assert sample_service.organisation_id == sample_organisation.id
-    assert len(AnnualBilling.query.all()) == 0
-
-
 def test_rest_get_organisation_services(
         admin_request, sample_organisation, sample_service):
     dao_add_service_to_organisation(sample_service, sample_organisation.id)