Trouble With Copying Dictionaries And Using Deepcopy On An Sqlalchemy Orm Object

I'm doing a Simulated Annealing algorithm to optimise a given allocation of students and projects. This is language-agnostic pseudocode from Wikipedia: s ← s0; e ← E(s)

Solution 1:

I have another possible solution: use transactions. This probably still isn't the best solution but implementing it should be faster.

Firstly create your session like this:

# transactional sessionSession = sessionmaker(transactional=True)
sess = Session()

That way it will be transactional. The way transactions work is that sess.commit() will make your changes permanent while sess.rollback() will revert them.

In the case of simulated annealing you want to commit when you find a new best solution. At any later point, you can invoke rollback() to revert the status back to that position.

Solution 2:

You don't want to copy sqlalchemy objects like that. You could implement your own methods which make the copies easily enough, but that is probably not want you want. You don't want copies of students and projects in your database do you? So don't copy that data.

So you have a dictionary which holds your allocations. During the process you should never modify the SQLAlchemy objects. All information that can be modified should be stored in those dictionaries. If you need to modify the objects to take that into account, copy the data back at the end.