`get_prep_value` no longer called for JSONField

[Julie Rymer]

Hello, I just upgraded from django 4.1 to 4.2 and I have a custom JSONField with a get_prep_value() override that stopped working. After searching a bit, I saw that was because JSONField.get_prep_value() is no longer called in 4.2 (​5c23d9f0c32f166c81ecb6f3f01d5077a6084318).

I think this issue need a resolution either:

• JSONField should call get_prep_value() like all other fields type, because this is the method that the ​documentation tell us to override in custom fields. Otherwise we need to override get_db_prep_value() which is heavier and does not have the same purpose. I think simply replacing connection.ops.adapt_json_value(value, self.encoder) with connection.ops.adapt_json_value(self.get_prep_value(value), self.encoder) in JSONField.get_db_prep_value() would fix this

• If there is a good reason to no longer call get_prep_value(), this exception for JSONField should be clearly documented in ​custom get_prep_value() doc. It should also be added to ​Backwards incompatible changes in 4.2 release note because I got stuck with this issue with no warning when migrating.

PS: #34397 seems to be related but in fact is about Django 3.2 so it is not the current issue