Using that model, I see this migration:
# Generated by Django 2.0.8.dev20180716124449 on 2018-07-25 20:51
from django.db import migrations, models
class Migration(migrations.Migration):
initial = True
dependencies = [
]
operations = [
migrations.CreateModel(
name='Invoice',
fields=[
('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
('field1', models.IntegerField()),
('field2', models.IntegerField()),
],
options={
'abstract': False,
},
),
migrations.AlterUniqueTogether(
name='invoice',
unique_together={('field1', 'field2')},
),
]
If I've missed something, please be more explicit about the steps to reproduce the issue.