Tracking linked models being assigned/removed

[dracos]

This may not be possible, or I may have missed something obvious :) Say I have two models:

@pghistory.track(pghistory.Snapshot('author.snapshot'))
class Author(models.Model):
    name = models.CharField(max_length=100)

@pghistory.track(pghistory.Snapshot('book.snapshot'))
class Book(models.Model):
    title = models.CharField(max_length=100)
    author = models.ForeignKey(Author)

I have Book A by author AA and Book B by author BB. But it turns out Book B was actually written by AA. So I update the data:

>>> book = Book.objects.get(title='B')
>>> book.author = Author.objects.get(name='AA')
>>> book.save()

If I now look at the history of Book B, what I see is what you would expect:

>>> pghistory.models.AggregateEvent.objects.target(Book.objects.get(title='B')).order_by('pgh_created_at').values()
<AggregateEventQuerySet [
  {'pgh_diff': None,                  'pgh_id': 2, 'pgh_label': 'book.snapshot', 'pgh_data': {'id': 2, 'title': 'B', 'author_id': 2}, ... },
  {'pgh_diff': {'author_id': [2, 1]}, 'pgh_id': 3, 'pgh_label': 'book.snapshot', 'pgh_data': {'id': 2, 'title': 'B', 'author_id': 1}, ... }
]>

The history of Author AA, however is as follows:

>>> for i in pghistory.models.AggregateEvent.objects.target(Author.objects.get(name='AA')).order_by('pgh_created_at').values(): print(i)
{'pgh_id': 1, 'pgh_label': 'author.snapshot', 'pgh_data': {'id': 1, 'name': 'AA'}, 'pgh_diff': None, ... }
{'pgh_id': 1, 'pgh_label': 'book.snapshot', 'pgh_data': {'id': 1, 'title': 'A', 'author_id': 1}, 'pgh_diff': None, ... }
{'pgh_id': 3, 'pgh_label': 'book.snapshot', 'pgh_data': {'id': 2, 'title': 'B', 'author_id': 1}, 'pgh_diff': None, ... }

This does make perfect sense from AA's point of view, the Author B entry is new to it and the docs are clear that pgh_diff only shows the difference "between this event and the previous event on the same object with the same label.", but what ideally I would like is for that last row to include a diff like the one in the Book B history, saying the author ID had changed from 2 to 1. That way I can get a history of Author AA, being able to tell the difference between books being added as new entries, and added as transfers from other authors.

Is there a way to do this that I have missed/ haven't thought of?

[dracos]

Dunno if this is related or not(!), but I've opened https://github.com/Opus10/django-pghistory/pull/16 which lets target() receive a queryset/list of objects, not only one. I thought this potentially could be used for the above, in that you could call pghistory.models.AggregateEvent.objects.target(author_aa.books.all()) to then get the history of all of them at once, maybe. But even if not useful for this ticket, thought it might be more generically useful anyway.

[wesleykendall]

As mentioned in #16 , this was deployed in version 1.4