相关模型更新模型字段更改

Question

What is the most proper way to trigger update of related models, when one of the fields of parent model is changed? I have this set of models:

class ActivityObject(models.Model):
    is_deleted = models.BooleanField(default=False)

class ActivityJob(models.Model):
    activity_object = models.ForeignKey(
        ActivityObject,
        related_name='activity_jobs',
    )
    is_deleted = models.BooleanField(default=False)

so if I set ActivityObject.is_deleted = True on some instance all I want is that all related instances of ActivityJob also changed field is_deleted to True . Thanks in advance.

Answer 1

Overriding save() will work:

class ActivityObject(models.Model):
    is_deleted = models.BooleanField(default=False)

    def save(self, *args, **kwargs):
        super(ActivityObject, self).save(args, kwargs)
        if self.is_deleted:
            for job in self.activity_jobs:
                job.is_deleted = True
                job.save()

Just guessing here, but if the real purpose of this is to delete ActivityJob s when related ActivityObject s are deleted, then you can just go ahead and delete the ActivityObject . Django's default behavior will remove all the ActivityJob s connected to it.

If you want to perform some other action when deleting, use Django's pre_delete or post_delete signals, which will call a function you define before/after deleting objects of the type you specify.

EDIT: if you ever use update() on querysets dealing with ActivityObject and changing is_deleted , you can either ensure that you perform a corresponding update() on ActivityJob , or you can override ActivityObject 's queryset functionality like this to make it happen automatically.

Answer 2

You can use Django signals' pre_delete or post_delete . More details and examples are available in the Django Signals documentation .