removing duplicated `user_id` def

* Fixing the specific issue

* Added an additional fix for a similar error in #529

Background:
- When an object is modified by SQLAlchemy, it is invalidated so need to be fetched again from the DB
- If there's an exception during a transaction, SQLAlchemy performs a rollback and mark the connection as dirty.

Bug:
- When handling exceptions, the exception handler tries to access the name of the cluster in the main object. Since the name has been invalidated due to a write, SQLAlchemy tries to fetch it on a 'dirty' connection and spits out an error. Solution:
- Fetch the information for handling the exception before starting the process.

…reign keys based on the signature.

It supports also sqlite using batch migrations