Comparing two unsaved model objects

[yrdnsa@…]

if i do this:

User(email="exmple@…") == User(email="exmple22@…")

it will return True!

but if i save them- it will return False.
this is because the eq magic method tries to compare their PK's. if no pk it will return None. so None == None...

django.db.models.base line 383
def eq

[Moritz Sichert]

Changing the __eq__ method to check if the pk value is None would cause that all non-saved model objects would return False when being compared:

>>> o = MyModel(text='foo')
>>> o == o
False

[Alex Gaynor]

It doesn't have to, you can have it fall back to an identity comparison if the pks are None.

[Anssi Kääriäinen]

See also #11892, #16458

How about something like:

def __eq__(self, other):
    if not isinstance(other, Model):
        return False
    if self._get_pk_val() is None:
        return id(self) == id(other)
    # Symmetric
    if self._meta.concrete_class != other._meta.concrete_class:
        return False
    return self._get_pk_val() == other._get_pk_val()

Not tested...

[jcspray@…]

aakaariai's suggestion worked for me when I encountered this issue.

[Anssi Kääriäinen]

I think this one is duplicate of #18864 (it has a slightly bigger scope as it also deals with __hash__).

[Anssi Kääriäinen <akaariai@…>]

In 6af05e7a0f0e4604d6a67899acaa99d73ec0dfaa:

Fixed model.eq and hash for no pk value cases

The eq method now considers two instances without primary key value
equal only when they have same id(). The hash method raises
TypeError for no primary key case.

Fixed #18864, fixed #18250

Thanks to Tim Graham for docs review.