squashmigrations produces incorrect result when a RenameModel operation is performed on a ForeignKey target

[InvalidInterrupt]

Given a list of operations:

    operations = [
        migrations.CreateModel(
            name="Author",
            fields=[
                ("id",
                 models.AutoField(auto_created=True, primary_key=True, serialize=False,
                                  verbose_name="ID")),
            ]
        ),
        migrations.CreateModel(
            name="Book",
            fields=[
                ("id",
                 models.AutoField(auto_created=True, primary_key=True, serialize=False,
                                  verbose_name="ID")),
                ("author", models.ForeignKey(on_delete=models.deletion.PROTECT,
                                             to="testapp.Author")),
            ]
        ),
        migrations.RenameModel("Author", "Person"),
        migrations.AddField(model_name="person",
                            name="birthdate",
                            field=models.DateField()),
    ]

squashmigrations produces the result:

    operations = [
        migrations.CreateModel(
            name='Book',
            fields=[
                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
                ('author', models.ForeignKey(on_delete=django.db.models.deletion.PROTECT, to='testapp.author')),
            ],
        ),
        migrations.CreateModel(
            name='Person',
            fields=[
                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
                ('birthdate', models.DateField()),
            ],
        ),
    ]

There are two apparent problems with the result:

• The model with the ForeignKey field is created before the target of the ForeignKey
• The to parameter of the ForeignKey is not updated with the new model name (the final AddField operation is not necessary to cause this problem)

I believe this is caused by CreateModel.reduce() allowing optimization though operations that reference models which the model being created has a relationship to. Similar effects are likely to be caused by other migration patterns as well (I think Tim Graham may have found one here but as far as I can tell that's not the problem originally reported in that ticket)

[Mariusz Felisiak]

Sample project 1.

[Mariusz Felisiak]

Sample project 2.