#30741: Setting db_constraint=False to an existing column does not properly drop
the constraint
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Reporter: Scott Stafford | Owner: nobody
Type: Uncategorized | Status: new
Component: Migrations | Version: 2.2
Severity: Normal | Resolution:
Keywords: db_constraint, | Triage Stage:
migrations | Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Description changed by Scott Stafford:
Old description:
> Repro steps, using PostgreSQL and Django 2.2.4:
>
> 1. Create a new model with a normal, constrained ForeignKey, such as:
>
> {{{
> class Child(models.Model):
> parent = models.ForeignKey('myapp.Parent', related_name="+",
> on_delete=models.DO_NOTHING)
> }}}
>
> 2. Create a migration: python manage.py makemigrations
>
> 3. Add db_constraint=False, like so:
>
> {{{
> class Child(models.Model):
> parent = models.ForeignKey('myapp.Parent', related_name="+",
> on_delete=models.DO_NOTHING, db_constraint=False)
> }}}
>
> 4. Create a second migration: python manage.py makemigrations
>
> 5. Peep at the generated SQL. The first migration creates the
> constraint, and the second fails to remove it:
>
> {{{
> (.env) c:\wc\dbconstraintnotdropped>python manage.py sqlmigrate myapp
> 0001
> BEGIN;
> --
> -- Create model Parent
> --
> CREATE TABLE "myapp_parent" ("id" serial NOT NULL PRIMARY KEY);
> --
> -- Create model Child
> --
> CREATE TABLE "myapp_child" ("id" serial NOT NULL PRIMARY KEY, "parent_id"
> integer NOT NULL);
> ALTER TABLE "myapp_child" ADD CONSTRAINT
> "myapp_child_parent_id_af46d0ab_fk_myapp_parent_id" FOREIGN KEY
> ("parent_id") REFERENCES "myapp_parent" ("id") DEFERRABLE INITIALLY
> DEFERRED;
> CREATE INDEX "myapp_child_parent_id_af46d0ab" ON "myapp_child"
> ("parent_id");
> COMMIT;
>
> (.env) c:\wc\dbconstraintnotdropped>python manage.py sqlmigrate myapp
> 0002
> BEGIN;
> --
> -- Alter field submission on child
> --
> COMMIT;
> }}}
New description:
Repro steps, using PostgreSQL and Django 2.2.4:
1. Create a new model with a normal, constrained ForeignKey, such as:
{{{
class Child(models.Model):
parent = models.ForeignKey('myapp.Parent', related_name="+",
on_delete=models.DO_NOTHING)
}}}
2. Create a migration: python manage.py makemigrations
3. Add db_constraint=False, like so:
{{{
class Child(models.Model):
parent = models.ForeignKey('myapp.Parent', related_name="+",
on_delete=models.DO_NOTHING, db_constraint=False)
}}}
4. Create a second migration: python manage.py makemigrations
5. Peep at the generated SQL. The first migration creates the constraint,
and the second fails to remove it:
{{{
(.env) c:\wc\dbconstraintnotdropped>python manage.py sqlmigrate myapp 0001
BEGIN;
--
-- Create model Parent
--
CREATE TABLE "myapp_parent" ("id" serial NOT NULL PRIMARY KEY);
--
-- Create model Child
--
CREATE TABLE "myapp_child" ("id" serial NOT NULL PRIMARY KEY, "parent_id"
integer NOT NULL);
ALTER TABLE "myapp_child" ADD CONSTRAINT
"myapp_child_parent_id_af46d0ab_fk_myapp_parent_id" FOREIGN KEY
("parent_id") REFERENCES "myapp_parent" ("id") DEFERRABLE INITIALLY
DEFERRED;
CREATE INDEX "myapp_child_parent_id_af46d0ab" ON "myapp_child"
("parent_id");
COMMIT;
(.env) c:\wc\dbconstraintnotdropped>python manage.py sqlmigrate myapp 0002
BEGIN;
--
-- Alter field submission on child
--
COMMIT;
}}}
Presumably related to the changes made on ticket:23264.
--
--
Ticket URL: <https://code.djangoproject.com/ticket/30741#comment:1>
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