[Django] #29260: Django makes an extra UPDATE query when custom PK is evaluating before save.

[Django]

#29260: Django makes an extra UPDATE query when custom PK is evaluating before
save.
-------------------------------------+-------------------------------------
               Reporter:  user0007   |          Owner:  nobody
                   Type:  Bug        |         Status:  new
              Component:  Database   |        Version:  2.0
  layer (models, ORM)                |
               Severity:  Normal     |       Keywords:
           Triage Stage:             |      Has patch:  0
  Unreviewed                         |
    Needs documentation:  0          |    Needs tests:  0
Patch needs improvement:  0          |  Easy pickings:  0
                  UI/UX:  0          |
-------------------------------------+-------------------------------------
 Using model's instance:

 {{{

 class Account(models.Model):
     id = models.UUIDField(
         primary_key=True,
         default=uuid.uuid4,
         editable=False
     )
     title = models.TextField()

 >> account = Account()
 >> account.title = "abc"
 >> account.save()

 1. UPDATE "app_account" SET "title" = \'\', WHERE "app_account"."id" =
 \'67c9327d-150e-419f-b493-0c2c59a045c3\'::uuid',
 2. INSERT INTO "app_account" ("title", "id") VALUES (\'abc\', \'3d8c1b3c-
 214a-4798-a0fa-d4c22c2b877f\'::uuid)

 }}}

 Using model's manager method:

 {{{
 >> Account.objects.create(title="abc")

 1. INSERT INTO "app_account" ("title", "id") VALUES (\'abc\', \'3d8c1b3c-
 214a-4798-a0fa-d4c22c2b877f\'::uuid)
 }}}


 Related issue? https://code.djangoproject.com/ticket/29129

-- 
Ticket URL: <https://code.djangoproject.com/ticket/29260>
Django <https://code.djangoproject.com/>
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