Cannot sqlmigrate on Django migrations that change unique_together

[Brіаn Lаі]

Somewhat similar to #26624, but forward sqlmigrate, reproduced on Django 3.0.8 and Postgres 10.x.

If a model with a unique_together of

unique_together = [
    (a, b)
]

and then this becomes

unique_together = [
    (a, b, c)
]

, although the makemigrations command successfully generates the corresponding AlterUniqueTogether() operation, the operation cannot be inspected with the sqlmigrate command.

Reproduce bug with the following (the project may also be attached)

class Model1(models.Model):
    id = models.IntegerField(primary_key=True)
    name = models.CharField(max_length=255, unique=True)


class Model2(models.Model):
    id = models.IntegerField(primary_key=True)
    link_id = models.CharField(max_length=255)
    settings = models.ForeignKey(Model1, on_delete=models.CASCADE)


class Model3(models.Model):
    id = models.IntegerField(primary_key=True)
    order = models.IntegerField()
    model_2 = models.ForeignKey(Model2, on_delete=models.CASCADE)
    direct = models.BooleanField(default=True)

    class Meta:
        unique_together = [
            ('model_2', 'order')
            # To get the bug, change this to ('model_2', 'order', 'direct') and sqlmigrate the migration that this creates.
        ]

[Brіаn Lаі]

Bug demo project