Proper way of avoiding to store the same attachment twice
I think building a wizard is the only way that will work, because there isn't a real link between attachment and project.task. If I were you, I would build a wizard that walks the parent relation to build a list of all ancestor task ids, plus the current task id. Then have the wizard open the attachment window using that list of ids as one of the domain search criteria.
I'm using the project.task model where delegation creates a parent/child link between both.
When delegating I would like the person who gets the delegated task to also have access to the attachments on the original task, how could I avoid to have to really copy it?
I've thought about using an <act_window> or a wizard which checks if there is a parent task and if so (also) show the parent task attachments.
The problem with act_window is that you would need to specify 2 different act_window records and that would still only cover one parent and one child relation (the task could be delegated more)
For the wizard approach it seems to be a lot of overkill work for something that could maybe be solved easier (hence the question).