id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
36401	Adding CompositePrimaryKey to exiting table leads to drop existing PK with not composit PK creation	Pavel Tyslacki		"When I define new table with `CompositePrimaryKey`:

{{{
class Test1(models.Model):
    pk = models.CompositePrimaryKey(""product_id"", ""order_id"")
    product_id = models.BigIntegerField()
    order_id = models.BigIntegerField()
    quantity = models.IntegerField()
}}}

if creates table with 

{{{
        migrations.CreateModel(
            name='Test1',
            fields=[
                ('pk', models.CompositePrimaryKey('product_id', 'order_id', blank=True, editable=False, primary_key=True, serialize=False)),
                ('product_id', models.BigIntegerField()),
                ('order_id', models.BigIntegerField()),
                ('quantity', models.IntegerField()),
            ],
        ),
}}}

and final SQL:

{{{
CREATE TABLE ""blog_test1"" (""product_id"" bigint NOT NULL, ""order_id"" bigint NOT NULL, ""quantity"" integer NOT NULL, PRIMARY KEY (""product_id"", ""order_id""));
}}}

But if I has existing table:

{{{
class Test2(models.Model):
    #pk = models.CompositePrimaryKey(""product_id"", ""order_id"")
    product_id = models.BigIntegerField()
    order_id = models.BigIntegerField()
    quantity = models.IntegerField()
}}}

{{{
         migrations.CreateModel(
            name='Test2',
            fields=[
                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
                ('product_id', models.BigIntegerField()),
                ('order_id', models.BigIntegerField()),
                ('quantity', models.IntegerField()),
            ],
        ),
}}}

and try to add `CompositePrimaryKey`, in this case next migration created:


{{{
        migrations.RemoveField(
            model_name='test2',
            name='id',
        ),
        migrations.AddField(
            model_name='test2',
            name='pk',
            field=models.CompositePrimaryKey('product_id', 'order_id', blank=True, editable=False, primary_key=True, serialize=False),
        ),
}}}

and migration SQL will look next:

{{{
--
-- Remove field id from test2
--
ALTER TABLE ""blog_test2"" DROP COLUMN ""id"" CASCADE;
--
-- Add field pk to test2
--
-- (no-op)
}}}

in this case old PK will be dropped, but new CompositePrimaryKey will not created.

Expected no matter is model created in one or two steps, final db table will have same PK constraints, eg. CompositePrimaryKey will be created if we add it to existing table.

Issue presented at least in postgres and sqlite
"	Bug	new	Migrations	5.2	Normal			Pavel Tyslacki	Unreviewed	0	0	0	0	0	0