PsqlDosMigrator: Commit changes when migrating existing schema

There was a bug in the `PsqlDosMigrator.migrate` method where the final
step of migrating a database with a pre-existing schema to the latest
schema version, would not be committed. This would manifest itself if a
new database migration was added. When the user requested to migrate the
storage, the migration would be performed, but since it wasn't committed
as soon as the command terminated, the changes would be undone.

The fix is to explicitly commit the changes in `migrate` after the final
migration to the head version, by calling `Connection.commit`. A test is
added to explicitly test the pathway of migrating a database with a
pre-existing schema to the head version.

aiida/storage/psql_dos/migrator.py

@@ -384,6 +384,7 @@ def migrate(self) -> None:
         # finally migrate to the main head revision
         MIGRATE_LOGGER.report('Migrating to the head of the main branch')
         self.migrate_up('main@head')
+        self.connection.commit()
 
     def migrate_up(self, version: str) -> None:
         """Migrate the database up to a specific version.

tests/storage/psql_dos/migrations/test_all_schema.py

@@ -21,6 +21,27 @@ def test_main(version, uninitialised_profile, reflect_schema, data_regression):
     data_regression.check(reflect_schema(uninitialised_profile))
 
 
+def test_main_initialized(uninitialised_profile):
+    """Test that ``migrate`` properly stamps the new schema version when updating database with existing schema."""
+    migrator = PsqlDosMigrator(uninitialised_profile)
+
+    # Initialize database at first version of main branch
+    migrator.migrate_up('main@main_0001')
+    assert migrator.get_schema_version_profile(check_legacy=False) == 'main_0001'
+    migrator.close()
+
+    # Reinitialize the migrator to make sure we are fetching actual state of database and not in-memory state and then
+    # migrate to head schema version.
+    migrator = PsqlDosMigrator(uninitialised_profile)
+    migrator.migrate()
+    migrator.close()
+
+    # Reinitialize the migrator to make sure we are fetching actual state of database and not in-memory state and then
+    # assert that the database version is properly set to the head schema version
+    migrator = PsqlDosMigrator(uninitialised_profile)
+    assert migrator.get_schema_version_profile(check_legacy=False) == migrator.get_schema_version_head()
+
+
 def test_head_vs_orm(uninitialised_profile, reflect_schema, data_regression):
     """Test that the migrations produce the same database schema as the models."""
     migrator = PsqlDosMigrator(uninitialised_profile)