Question

Command pattern can be used to implement Transactional behavior (and Undo).
But I could not find an example of these by googling. I could only find some trivial examples of a lamp that is switched on or off.
Where can I find a coding example (preferably in Java)of this/these behaviors implemented using the Command Pattern?

Answer 1

In one of our projects, we have the following requirement:

1. Create a record in DB.
2. Call a service to update a related record.
3. Call another service to log a ticket.

To perform this in a transactional manner, each operation is implemented as a command with undo operation. At the end of each step, the command is pushed onto a stack. If the operation fails at some step, then we pop the commands from the stack and call undo operation on each of the command popped out. The undo operation of each step is defined in that command implementation to reverse the earlier command.execute().

Hope this helps.