Get all related Django model objects

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!

Answers:

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Method 1

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)

Method 2

@digitalPBK was close… here is probably what you are looking for using Django’s built-in stuff that is used in Django admin for displaying related objects during deletion

from django.contrib.admin.utils import NestedObjects
collector = NestedObjects(using="default") #database name
collector.collect([objective]) #list of objects. single one won't do
print(collector.data)

this allows you to create what the Django admin displays – the related objects to be deleted.

Method 3

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]

Method 4

The following is what django uses to get all related objects

from django.db.models.deletion import Collector
collector = Collector(using="default")
collector.collect([a])

print collector.data

Method 5

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

Method 6

for link in links:
    objects = getattr(a, link).all()

Works for related sets, but not for ForeignKeys. Since RelatedManagers are created dynamically, looking at the class name is easier than doing an isinstance()

objOrMgr = getattr(a, link)
 if objOrMgr.__class__.__name__ ==  'RelatedManager':
      objects = objOrMgr.all()
 else:
      objects = [ objOrMgr ]
 for object in objects:
      # Do Stuff

Method 7

Django 1.9
get_all_related_objects() has been deprecated

#Example: 
user = User.objects.get(id=1)
print(user._meta.get_fields())

Note:
RemovedInDjango110Warning: ‘get_all_related_objects is an unofficial API that has been deprecated. You may be able to replace it with ‘get_fields()’

Method 8

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.

Method 9

Here is another way to get a list of fields (names only) in related models.

def get_related_model_fields(model):
    fields=[]
    related_models = model._meta.get_all_related_objects()
    for r in related_models:
        fields.extend(r.opts.get_all_field_names())
    return fields

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0