Add a "ModelDelta" and "__sub__" method to have a timeline info

[leportella]

We needed to implement a timeline considering the changes made in a specific model. For that, we basically needed the "difference" between two records.

In order to do that, we created a __sub__ method that allowed us to simply do something like this:
history[1] - history[0].

The result of this operation is an instance of a class called ModelDelta, that gives us the following information:

• the new value
• the old value
• the fields that changed in the process
• user that made the change (to the new value)

On this ModelDelta class we implemented a function to_timeline that get every changed field and apply a function to create a timeline entry with some messages like This user changed this fields at this hour.

I would like to know if you would think this is interesting to be a feature in the project, and if you have suggestion for better approach.

[bmampaey]

I would be very interested in such a functionality, as I need the same thing in my project.

Could you already share the code with us? Either with a pull or a djangosnippet?

[michi88]

@leportella Yes! I would love to see this going as a django admin view. There is an old PR #103 that adds a history compare view. Maybe we can combine the 2? Happy to help!

[rossmechanic]

Closed by #416