Get all related Django model objects
Question:
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:
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]
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)
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
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
@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.
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
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()’
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.
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
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!
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]
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)
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
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
@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.
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
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()’
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.
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