#32634: AlterField drops contraints in the wrong order when performed as reverse
migration
----------------------------------+--------------------------------------
Reporter: Matthias Dellweg | Owner: nobody
Type: Bug | Status: new
Component: Migrations | Version: 3.2
Severity: Normal | Resolution:
Keywords: | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Changes (by Matthias Dellweg):
* status: closed => new
* version: 2.2 => 3.2
* resolution: needsinfo =>
Comment:
I could reproduce with Django==3.2.
I created a sample project here:
https://github.com/mdellweg/migrationtest
If you configure this app to a postgres driver and call
`migrationtest/manage.py sqlmigrate --backwards pk_migration 0002`, you
will see:
{{{
BEGIN;
--
-- Alter field secondbase_ptr on child
--
SET CONSTRAINTS
"pk_migration_child_secondbase_ptr_id_9b785ce8_fk_pk_migrat" IMMEDIATE;
ALTER TABLE "pk_migration_child" DROP CONSTRAINT
"pk_migration_child_secondbase_ptr_id_9b785ce8_fk_pk_migrat";
ALTER TABLE "pk_migration_child" ALTER COLUMN "secondbase_ptr_id" DROP NOT
NULL;
ALTER TABLE "pk_migration_child" DROP CONSTRAINT
"pk_migration_child_secondbase_ptr_id_9b785ce8_pk";
ALTER TABLE "pk_migration_child" ADD CONSTRAINT
"pk_migration_child_secondbase_ptr_id_9b785ce8_uniq" UNIQUE
("secondbase_ptr_id");
ALTER TABLE "pk_migration_child" ADD CONSTRAINT
"pk_migration_child_secondbase_ptr_id_9b785ce8_fk_pk_migrat" FOREIGN KEY
("secondbase_ptr_id") REFERENCES "pk_migration_secondbase" ("id")
DEFERRABLE INITIALLY DEFERRED;
--
-- Remove field firstbase_ptr from child
--
ALTER TABLE "pk_migration_child" ADD COLUMN "firstbase_ptr_id" bigint NOT
NULL PRIMARY KEY CONSTRAINT
"pk_migration_child_firstbase_ptr_id_3ea33ffb_fk_pk_migrat" REFERENCES
"pk_migration_firstbase"("id") DEFERRABLE INITIALLY DEFERRED; SET
CONSTRAINTS "pk_migration_child_firstbase_ptr_id_3ea33ffb_fk_pk_migrat"
IMMEDIATE;
--
-- MIGRATION NOW PERFORMS OPERATION THAT CANNOT BE WRITTEN AS SQL:
-- Raw Python operation
--
--
-- Add field secondbase_ptr to child
--
SET CONSTRAINTS
"pk_migration_child_secondbase_ptr_id_9b785ce8_fk_pk_migrat" IMMEDIATE;
ALTER TABLE "pk_migration_child" DROP CONSTRAINT
"pk_migration_child_secondbase_ptr_id_9b785ce8_fk_pk_migrat";
ALTER TABLE "pk_migration_child" DROP COLUMN "secondbase_ptr_id" CASCADE;
COMMIT;
}}}
Which will fail to migrate with `column "secondbase_ptr_id" is in a
primary key` when trying to execute `ALTER TABLE "pk_migration_child"
ALTER COLUMN "secondbase_ptr_id" DROP NOT NULL;`.
If you move `ALTER TABLE "pk_migration_child" DROP CONSTRAINT
"pk_migration_child_secondbase_ptr_id_9b785ce8_pk";` one place up in the
command chain, the migration will succeed.
--
Ticket URL: <https://code.djangoproject.com/ticket/32634#comment:2>
Django <https://code.djangoproject.com/>
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