Note: New to django. Doing my with project with it. So I certainly lack many understand and the answer could be trivial.
I have a ManyToMany relationship. I have trouble coming up with an analogy but on the "main" side we have a container which contains one or more items. In my case the items aren't "real" things but more like a "template" and templates are unique. This is the background.
The business rules are that changes only happen and are initiated on the container side. So the form shows a container an it's items. A user can change one of the items. If an item in a container changes, the item instance (row in database) must not change, as said, it's a template used in many other containers. So the logic must be that if a user changes an item, a lookup is done if it already exists and if yes, instead of updating the current item, reuse the existing one. If it doesn't exist, create a new one and use that. But under no circumstance should the existing one be changed.
How and where (at which level) can I achieve this? I would really like to keep this out of the model itself (and hence not override the models save method) but do it in some type of service class.
Not really an answer but it seems with how django works doing this in the models save() method is the correct way to go.