History changes do not get tracked for ManyToMany field

[martasd]

I have a model called Beo with a ManyToMany field organizers using a through model as suggested here:

class Beo(HistoryModel):
    ...
    organizers = ManyToManyField(
        UserProfile, related_name="organized_beos", blank=True,
        through="BeoOrganizer", through_fields=("beo", "organizer")
    )


class BeoOrganizer(HistoryModel):
    beo = ForeignKey(Beo, on_delete=CASCADE)
    organizer = ForeignKey(UserProfile, related_name="organized_beo", on_delete=CASCADE)

    class Meta(HistoryModel.Meta):
        verbose_name = "beo organizer"
        verbose_name_plural = "beo organizers"

    def __str__(self):
        return f"{self.beo} - {self.organizer}"

To use django-simple-history with multiple models, I have created an abstract class called HistoryModel, which creates historical records:

class HistoryModel(BaseModel):
    class Meta(BaseModel.Meta):
        abstract = True

    # History
    changed_by = ForeignKey(UserProfile, on_delete=SET_NULL, null=True, blank=True)
    history = HistoricalRecords(
        user_model=UserProfile, inherit=True, excluded_fields=["modified_at"]
    )

    @property
    def _history_user(self):
        return self.changed_by

    @_history_user.setter
    def _history_user(self, value):
        # History user can only be a user profile, not admin user
        if isinstance(value, SystemUser):
            self.changed_by = None
        else:
            self.changed_by = value

When I make changes to a Beo instance, history gets recorded as expected for beo instance itself. Everything works well here. When I make changes to organizers of a beo, however, the only changes recorded in beo_historicalbeoorganizer table are deletions (history_type is -). Neither creations nor updates get recorded.

To Reproduce
Steps to reproduce the behavior:

1. Create a Django model with history containing a ManyToMany field using through model
2. Create the through model with history
3. Create a new instance of the first model with a value in the ManyToMany field.
4. + history_type record DOES NOT get created for the ManyToMany field.

Expected behavior
+ history_type record DOES get created for the ManyToMany field.

Environment

• OS: Debian GNU/Linux 10
• Django Simple History Version: 2.8
• Django Version: 2.2.5
• Database Version: PostgreSQL 11.6

[rossmechanic]

How are you calling these? As beo.add(beo_organizer)? I think they should send a post_save signal to add those changes – however, if they don't we can hook simple history into the m2m_changed signal and get it working there. I'd be happy to look at a PR if you want to take a shot at one.

[martasd]

When I call beo.organizers.add(user), the user does get added to the beo as expected, but the historical record does not get created. Could you please point me to the right place in the code to add this?

[rossmechanic]

https://github.com/treyhunner/django-simple-history/blob/b96a8fddafcb314fd7c2a8e4c48ab5d6045ef07a/simple_history/models.py#L163-L166

That's where we connect to post_save and post_delete signals. Would also want to connect to the m2m_changed signal

[martasd]

Thanks. I will take a look.

[carolynlawrence]

Just wanted to chime in here that I've just run into this issue, and a quick work-around that seems to be working ok for me to at least get create changes to be recorded is to call create instead of add, e.g. for @martasd code example above:

BeoOrganizer.objects.create(beo=beo_instance, organizer=organizer_instance)

instead of

beo_instance.organizers.add(organizer_instance)

[jeking3]

Also see #399

[ddabble]

This seems either resolved or stale, so closing. Please reopen if that's not the case 🙂