Include serialized model data when validating

[john-parton]

Description

Potential fix for: #7489

When an instance is passed to a ModelSerializer, we might need fields
that aren't specified in initial_data to run a validator. Specifically
for UniqueTogether

More details

There's potentially a backwards-incompatible change, that should at the very least be documented.

Previously there could be a dirty value in the database, and so long as you didn't try to touch it, it wouldn't cause re-validation.

For instance, suppose you have a validator on some_bad_field that prohibits "bad_value", and another unrelated field 'foo'.

# OK
instance = MyModel.objects.create(some_bad_field='bad_value')

# Old way didn't complain
serializer = MyModelSerializer(instance=instance, data={'foo': 'bar'})

# New way will re-validate ALL the fields, including some_bad_field, and fail
serializer = MyModelSerializer(instance=instance, data={'foo': 'bar'})

Whether that's desirable behavior or not should probably be discussed.

[john-parton]

I found some tests that were failing with the previous change.

I reworked it so that this behavior is opt-in, but now the tests don't necessarily cover this case.

Is this a desirable change, or should I abandon this?

Still needs docs.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[auvipy]

I don't think adding a new settings is a good idea at this stage of the project