Document how to migrate project using <0.4 to >= 0.4

[makinacorpus]

Document how to migrate project using <0.4 to >= 0.4

[hvdklauw]

This is a way to do it if you don't care about backwards compatibility or running multiple version of your code against the same database.

If you for instance want to update one frontend while keeping the old running this is not for you.

from __future__ import unicode_literals

from django.db import migrations, models


def migrate_deleted(apps, schema_editor):
    db_alias = schema_editor.connection.alias
    Model = apps.get_model('app', 'Model')
    for obj in Model.objects.using(db_alias).all():
        if obj.deleted:
            obj.deleted_at = obj.modified
            obj.save()


class Migration(migrations.Migration):

    dependencies = [
        ('app', '0001_initial'),
    ]

    operations = [
        migrations.AddField(
            model_name='model',
            name='deleted_at',
            field=models.DateTimeField(editable=False, null=True),
        ),
        migrations.RunPython(migrate_deleted, migrations.RunPython.noop),
        migrations.RemoveField('Model', 'deleted'),
        migrations.RenameField(
            model_name='model',
            old_name='deleted_at',
            new_name='deleted',
        ),
    ]

[Gagaro]

We discussed it in #55. I don't have time right now but I will definitively add some documentation about how to migrate later.

If someone is willing to do it before then, don't hesitate to do a PR.

[hvdklauw]

Did some more thinking about this.

Just renaming the columns is not going to work for anything with more then one frontend (unless you are willing to take some downtime).

You need to be able to put the new code on one frontend, run the migrations and still keep the old code working with the database.
It would have been better if the deleted column was renamed to deleted_at then it could have just been added (it's nullable, so old code keeps working) and after a while you could delete the old column.

[BeOleg]

Yup this is indeed missing