E736. Undo Functionality for Expertiza

Contacts: Ed Gehringer (efg@ncsu.edu) and Andrew Kofink (ajkofink@ncsu.edu)
Begin implementing SQL transactions (ActiveRecord:Transactions). This should let the user "roll back" any creation or update of a SQL table (assignments, rubrics, etc.) Several issues arise, that you should discuss with me.
- Should students be able to roll back, e.g., submissions or reviews?
- Suppose an instructor is trying to roll back and a TA is editing the same assignment? How can conflicts be presented?
- Do rollbacks affect only what's in the db, or do they also affect submitted files?
Project Description Doc

Team Members

Undo should cover any edit functionalities and any submissions of links. File submissions do not need to be included for the scope of this project.
User should be able to undo any changes to an item (such as course or assignment) as long as no other user has edited that same item within the user's current session.
If undo is attempted on an item already modified by another user, display a message stating why undo cannot be done.

DRY
- "Don't Repeat Yourself" practice will be followed.
Memento
- The memento pattern is a software design pattern that provides the ability to restore an object to its previous state (undo via rollback). The memento pattern is implemented with two objects: the originator and a caretaker. The originator is some object that has an internal state. The caretaker is going to do something to the originator, but wants to be able to undo the change. The caretaker first asks the originator for a memento object. Then it does whatever operation (or sequence of operations) it was going to do. To roll back to the state before the operations, it returns the memento object to the originator. The memento object itself is an opaque object (one which the caretaker cannot, or should not, change). When using this pattern, care should be taken if the originator may change other objects or resources - the memento pattern operates on a single object. Classic examples of the memento pattern include the seed of a pseudorandom number generator (it will always produce the same sequence thereafter when initialized with the seed state) and the state in a finite state machine.
- The Memento pattern will be followed through open-source Ruby gems leveraged by the project.

Every class method modified will be tested via unit test.
Every new method added will be tested via at least one unit test.
All test methods shall be named with an appropriately descriptive name that is not too long.

The following functional test plans will be followed for all items enhanced with the Undo functionality:
- Test that an item may be changed, then undo performed successfully.
- Test that a sequence of changes may be performed by one user, then undo performed successfully for each action from the sequence.
- Test that an item may be changed by one user, changed again by another user, then undo performed by the original user will display a failure message with description.