Get all related Django model objects

user_126617 0
Viewed 56582

How can I get a list of all the model objects that have a ForeignKey pointing to an object? (Something like the delete confirmation page in the Django admin before DELETE CASCADE).

I'm trying to come up with a generic way of merging duplicate objects in the database. Basically I want all of the objects that have ForeignKeys points to object "B" to be updated to point to object "A" so I can then delete "B" without losing anything important.

Thanks for your help!

merge django-models django python
9 Answers

Django <= 1.7

This gives you the property names for all related objects:

links = [rel.get_accessor_name() for rel in a._meta.get_all_related_objects()]

You can then use something like this to get all related objects:

for link in links:
    objects = getattr(a, link).all()
    for object in objects:
        # do something with related object instance

I spent a while trying to figure this out so I could implement a kind of "Observer Pattern" on one of my models. Hope it's helpful.

Django 1.8+

Use _meta.get_fields(): https://docs.djangoproject.com/en/1.10/ref/models/meta/#django.db.models.options.Options.get_fields (see reverse in the _get_fields() source also)

user_2790890

Give this a try.

class A(models.Model):
    def get_foreign_fields(self):
      return [getattr(self, f.name) for f in self._meta.fields if type(f) == models.fields.related.ForeignKey]
user_2349690

links = [rel.get_accessor_name() for rel in a._meta.get_all_related_objects()]

You can then use something like this to get all related objects:

for link in links:
    objects = getattr(a, link.name).all()
    for object in objects:
        # do something with related object instance

From Django 1.10 offical docs:

MyModel._meta.get_all_related_objects() becomes:

[
    f for f in MyModel._meta.get_fields()
    if (f.one_to_many or f.one_to_one)
    and f.auto_created and not f.concrete
]

So by taking the approved example we would use:

links = [
            f for f in MyModel._meta.get_fields()
            if (f.one_to_many or f.one_to_one)
            and f.auto_created and not f.concrete
        ]

for link in links:
    objects = getattr(a, link.name).all()
    for object in objects:
        # do something with related object instance
user_5480590

Unfortunately, user._meta.get_fields() returns only relations accessible from user, however, you may have some related object, which uses related_name='+'. In such case, the relation would not be returned by user._meta.get_fields(). Therefore, if You need generic and robust way to merge objects, I'd suggest to use the Collector mentioned above.

user_70617580
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