Hello HM,
I know that some changes have been made to avoid unnecessary foreign key
rebuilds on some option changes.
Are you experiencing this on 2.1 and 2.2 pre release?
Simon
Le vendredi 1 mars 2019 02:40:01 UTC-5, HM a écrit :
>
> I added "related_name" to an exiting ForeignKey and checked with
> "django-admin sqlmigrate" what would be done.
>
> It seems that the foreign key constraint is dropped, then the exact
> same constraint is added back. Why?
>
> Example: If we have the classes:
>
> class Wall(models.Model):
> ..
>
> class Door(models.Model):
> ..wall = models.ForeignKey(Wall)
>
> and change Door.wall to models.ForeignKey(Wall, related_name='walls'),
> then:
>
> Prior to this, there exist (postgres) the constraint:
>
> "app_door_wall_id_45647_fk_app_wall" FOREIGN KEY (wall_id) REFERENCES
> app_wall(id) DEFERRABLE INITIALLY DEFERRED.
>
> "django_admin sqlmigrate" reports:
>
> SET CONSTRAINTS "app_door_wall_id_45647_fk_app_wall" IMMEDIATE; ALTER
> TABLE "app_door" DROP CONSTRAINT
> "app_door_wall_id_45647_fk_app_wall";
> ALTER TABLE "app_door" ADD CONSTRAINT
> "app_door_wall_id_45647_fk_app_wall" FOREIGN KEY ("wall_id")
> REFERENCES "app_wall" ("id") DEFERRABLE INITIALLY DEFERRED;
>
> After running the migration, which is run as there's stuff in the log,
> there exists seemingly the same constraint as before:
>
> "app_door_wall_id_45647_fk_app_wall" FOREIGN KEY (wall_id) REFERENCES
> app_wall(id) DEFERRABLE INITIALLY DEFERRED.
>
> Why waste a connection this way?
>
> --
> HM
>
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