Django ORM - objects.filter() vs. objects.all().filter() - which one is preferred?

The method all() on a manager just delegates to get_queryset(), as you can see in the Django source code:

def all(self):    return self.get_queryset()

So it's just a way to get the QuerySet from the Manager. This can be handy to ensure that you're dealing with a QuerySet and not a Manager, because MyModel.objects returns a Manager.

For example, if you want to iterate over all the items, you can't do this:

for item in MyModel.objects:    # do something with item

Because you can't iterate over a Manager. However, all() returns the QuerySet, you can iterate over a QuerySet:

for item in MyModel.objects.all():    # do something with item

Generally, you should never overwrite all(). You can overwrite get_queryset() but this method must return a QuerySet.

If you would use a filter method like filter() or exclude(), you would already have the QuerySet, because these methods are proxied to the QuerySet. So you don't have to do something like all().filter().

1. MyModel.objects returns the manager instance. all() return get_query_set(). I think all is there for when you need all objects.
2. I prefer MyModel.objects.filter() cause the other is just one more method call, and I don't need all objects if I do filter :)
3. It depends on the purpose. But if they override a base method of the manager, they return the same result format (eg. a QuerySet)

Mymodel.objects.filter(username='abcd') will give list of match recordMymodel.objects.get(pk='abcd') will return single record with matching on primary key value