Behavior of Model.delete() with regards to primary_key fields is not documented

[SwampFalc]

When .delete() is called on a model instance, the primary_key field of that instance is set to None (​https://github.com/django/django/blob/main/django/db/models/deletion.py#L456).

For a "standard" autoincrement PK, this is fine. However, if you have defined an actual data field as primary_key on the model, this data is lost in the instance.

This is counter to what is stated in the basic documentation about "Deleting objects" (​https://docs.djangoproject.com/en/4.1/ref/models/instances/#deleting-objects): "This only deletes the object in the database; the Python instance will still exist and will still have data in its fields."

There is also no mention of this in the documentation of "primary_key" (​https://docs.djangoproject.com/en/4.1/ref/models/fields/#primary-key) or the more in-depth documentation about "Deleting objects" (​https://docs.djangoproject.com/en/4.1/topics/db/queries/#deleting-objects).

I feel that this should at the very least be mentioned in the "primary_key" documentation, perhaps in some of the other locations too.

If an agreement can be reached about where it should be mentioned and where not, I am willing to create a pull request.

[SwampFalc]

You know, thinking about it some more... What exactly is the reason for setting the PK to None upon deletion? Is that really necessary?

Should it perhaps only happen when the PK is an autoincrement? Or should it perhaps not happen at all?

[Carlton Gibson]

I think something as small as... "the Python instance will still exist and will still have data in its fields, but the primary key is set to None" in the ​Deleting objects docs you point to, would likely be enough.

You know, thinking about it some more... What exactly is the reason for setting the PK to None upon deletion? Is that really necessary?

Standardly, whether the object has a PK is the test whether it's been saved (i.e. exists in the DB). I doubt that's changeable.
(Others may give a better account.)

[noFFENSE]

Please, tell me if something is wrong, and I will fix it, that's only my 2nd contribution, so I do not know whether I did a good job or not

[Mariusz Felisiak]

Please don't mark your own PRs as "Ready for checkin".

[noFFENSE]

Replying to Mariusz Felisiak:

Please don't mark your own PRs as "Ready for check-in".

Okay, may I ask why?

[Carlton Gibson]

Have a read of the ​Triage Workflow docs — they explain the process.

(Basically, someone else needs to review your patch first.)

[Mariusz Felisiak <felisiak.mariusz@…>]

In 5cd13853:

Fixed #34242 -- Doc'd that primary key is set to None when deleting objects.

[Mariusz Felisiak <felisiak.mariusz@…>]

In fa52bb7:

[4.2.x] Fixed #34242 -- Doc'd that primary key is set to None when deleting objects.

Backport of 5cd1385356d4b275133ddb0f8c78b2f37c5901eb from main

[Mariusz Felisiak <felisiak.mariusz@…>]

In 2a32d39:

[4.1.x] Fixed #34242 -- Doc'd that primary key is set to None when deleting objects.

Backport of 5cd1385356d4b275133ddb0f8c78b2f37c5901eb from main