django-scheduler > 0.9.3 migrate throws error on MySQL

Hello devs,

after upgrading from version 0.9.3 to any later version, i get an error when trying to migrate. This is obviously related to the migration 0013 and MySQ…

Output when running migrations:

$ ./manage.py migrate
[...]
Running migrations:
  Applying schedule.0013_auto_20210502_2303...Traceback (most recent call last):
  File "/home/sgtest1/calendar/env/lib64/python3.8/site-packages/django/db/backends/utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
  File "/home/sgtest1/calendar/env/lib64/python3.8/site-packages/django/db/backends/mysql/base.py", line 73, in execute
    return self.cursor.execute(query, args)
  File "/home/sgtest1/calendar/env/lib64/python3.8/site-packages/MySQLdb/cursors.py", line 206, in execute
    res = self._query(query)
  File "/home/sgtest1/calendar/env/lib64/python3.8/site-packages/MySQLdb/cursors.py", line 319, in _query
    db.query(q)
  File "/home/sgtest1/calendar/env/lib64/python3.8/site-packages/MySQLdb/connections.py", line 259, in query
    _mysql.connection.query(self, query)
MySQLdb._exceptions.OperationalError: (1833, "Cannot change column 'event_ptr_id': used in a foreign key constraint 'event_calendar_event_eventinfo_id_50769baf_fk_event_cal' of table 'sgtest1.event_calendar_eventinfo_organizer'")

The above exception was the direct cause of the following exception:
Traceback (most recent call last):
  File "./manage.py", line 44, in <module>
    main()
  File "./manage.py", line 40, in main
    execute_from_command_line(sys.argv)
  File "/home/sgtest1/calendar/env/lib64/python3.8/site-packages/django/core/management/__init__.py", line 419, in execute_from_command_line
    utility.execute()
  File "/home/sgtest1/calendar/env/lib64/python3.8/site-packages/django/core/management/__init__.py", line 413, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/home/sgtest1/calendar/env/lib64/python3.8/site-packages/django/core/management/base.py", line 354, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/home/sgtest1/calendar/env/lib64/python3.8/site-packages/django/core/management/base.py", line 398, in execute
    output = self.handle(*args, **options)
  File "/home/sgtest1/calendar/env/lib64/python3.8/site-packages/django/core/management/base.py", line 89, in wrapped
    res = handle_func(*args, **kwargs)
  File "/home/sgtest1/calendar/env/lib64/python3.8/site-packages/django/core/management/commands/migrate.py", line 244, in handle
    post_migrate_state = executor.migrate(
  File "/home/sgtest1/calendar/env/lib64/python3.8/site-packages/django/db/migrations/executor.py", line 117, in migrate
    state = self._migrate_all_forwards(state, plan, full_plan, fake=fake, fake_initial=fake_initial)
  File "/home/sgtest1/calendar/env/lib64/python3.8/site-packages/django/db/migrations/executor.py", line 147, in _migrate_all_forwards
    state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
  File "/home/sgtest1/calendar/env/lib64/python3.8/site-packages/django/db/migrations/executor.py", line 227, in apply_migration
    state = migration.apply(state, schema_editor)
  File "/home/sgtest1/calendar/env/lib64/python3.8/site-packages/django/db/migrations/migration.py", line 126, in apply
    operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
  File "/home/sgtest1/calendar/env/lib64/python3.8/site-packages/django/db/migrations/operations/fields.py", line 244, in database_forwards
    schema_editor.alter_field(from_model, from_field, to_field)
  File "/home/sgtest1/calendar/env/lib64/python3.8/site-packages/django/db/backends/base/schema.py", line 608, in alter_field
    self._alter_field(model, old_field, new_field, old_type, new_type,
  File "/home/sgtest1/calendar/env/lib64/python3.8/site-packages/django/db/backends/base/schema.py", line 830, in _alter_field
    self.execute(
  File "/home/sgtest1/calendar/env/lib64/python3.8/site-packages/django/db/backends/base/schema.py", line 145, in execute
    cursor.execute(sql, params)
  File "/home/sgtest1/calendar/env/lib64/python3.8/site-packages/django/db/backends/utils.py", line 66, in execute
    return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)
  File "/home/sgtest1/calendar/env/lib64/python3.8/site-packages/django/db/backends/utils.py", line 75, in _execute_with_wrappers
    return executor(sql, params, many, context)
  File "/home/sgtest1/calendar/env/lib64/python3.8/site-packages/django/db/backends/utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
  File "/home/sgtest1/calendar/env/lib64/python3.8/site-packages/django/db/utils.py", line 90, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "/home/sgtest1/calendar/env/lib64/python3.8/site-packages/django/db/backends/utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
  File "/home/sgtest1/calendar/env/lib64/python3.8/site-packages/django/db/backends/mysql/base.py", line 73, in execute
    return self.cursor.execute(query, args)
  File "/home/sgtest1/calendar/env/lib64/python3.8/site-packages/MySQLdb/cursors.py", line 206, in execute
    res = self._query(query)
  File "/home/sgtest1/calendar/env/lib64/python3.8/site-packages/MySQLdb/cursors.py", line 319, in _query
    db.query(q)
  File "/home/sgtest1/calendar/env/lib64/python3.8/site-packages/MySQLdb/connections.py", line 259, in query
    _mysql.connection.query(self, query)
django.db.utils.OperationalError: (1833, "Cannot change column 'event_ptr_id': used in a foreign key constraint 'event_calendar_event_eventinfo_id_50769baf_fk_event_cal' of table 'sgtest1.event_calendar_eventinfo_organizer'")
Traceback (most recent call last):
  File "./scripts/init.py", line 87, in <module>
    exec_cmd(
  File "./scripts/init.py", line 59, in exec_cmd
    subprocess.run(
  File "/usr/lib64/python3.8/subprocess.py", line 516, in run
    raise CalledProcessError(retcode, process.args,
subprocess.CalledProcessError: Command '['./manage.py', 'migrate', '--skip-checks']' returned non-zero exit status 1.

System information:

$ mysql --version
mysql  Ver 15.1 Distrib 10.3.31-MariaDB, for Linux (x86_64) using readline 5.1
$ pip freeze
[...]
mysqlclient==2.0.3
sqlparse==0.4.2
uWSGI==2.0.19.1

[EsGeh]

Fixing this issue and migrating the database according to the changes introduced by django-scheduler > 0.9.3 was a nightmare. Finally I was able to fix this issue for my project. I am going to share my approach here in the hope of helping others to save time:

Given you have a model that depends on a Model in django-scheduler (python import: schedule):

import schedule.models as schedule
...
class EventInfo(schedule.Event):
    ...(other fields)...
    event_ptr = models.OneToOneField(
            schedule.Event,
            on_delete=models.CASCADE,
            parent_link = True,
            primary_key=True,
            related_name="event_info"
    )

We shall introduce 2 migrations:

your_app/migrations/0020_cut_foreign_keys.py:

from django.db import migrations, models
import django.db.models.deletion

def copy_to_backup(apps, schema_editor):
    EventInfo = apps.get_model('your_app', 'EventInfo')
    EventInfoBackup = apps.get_model('event_calendar', 'EventInfoBackup')
    for x in EventInfo.objects.all():
        copy = EventInfoBackup(
                event_ptr = x.pk,
                # ...other fields...
        )
        # for every ManyToManyField field "m2mField":
        # copy.m2mField.set(
        #         x.m2mField.all()
        # )
        copy.save()
    for x in EventInfo.objects.all():
        x.delete(
                keep_parents = True
        )

def copy_to_backup_reverse(apps, schema_editor):
    EventInfo = apps.get_model('your_app', 'EventInfo')
    EventInfoBackup = apps.get_model('your_app', 'EventInfoBackup')
    EventBase = apps.get_model( 'schedule', 'Event' )
    for copy in EventInfoBackup.objects.all():
        event = EventBase.objects.get(
                pk = copy.event_ptr
        )
        x = EventInfo(
                event_ptr = event,
                start = event.start,
                end = event.end,
                title = event.title,
                description = event.description,
                creator = event.creator,
                created_on = event.created_on,
                updated_on = event.updated_on,
                rule = event.rule,
                end_recurring_period = event.end_recurring_period,
                calendar = event.calendar,
                color_event = event.color_event,
        )
        x.event_ptr = event
        # for every field in EventInfo:
        # x.field = copy.field
        x.save()
        # for every ManyToManyField in EventInfo:
        x.m2mField.set(
                copy.m2mField.all()
        )
        x.save()


class Migration(migrations.Migration):

    dependencies = [
        ('you_app', '0019_...'), # <-- previous migration
        ('schedule', '0012_auto_20191025_1852'),
    ]

    run_before = [
        ('schedule', '0013_auto_20210502_2303'),
    ]

    operations = [
        migrations.CreateModel(
            name='EventInfoBackup',
            fields=[
                ('event_ptr', models.IntegerField(primary_key=True)),
                # ...other fields...
            ],
        ),
        # Copy EventInfos to backup
        migrations.RunPython(
            code = copy_to_backup,
            reverse_code = copy_to_backup_reverse
        ),
        migrations.DeleteModel(
            name = 'EventInfo',
        )
    ]

your_app/migrations/0021_repair_foreign_keys.py:

from django.db import migrations, models
import django.db.models.deletion


def copy_from_backup(apps, schema_editor):
    EventInfo = apps.get_model('your_app', 'EventInfo')
    EventInfoBackup = apps.get_model('your_app', 'EventInfoBackup')
    EventBase = apps.get_model( 'schedule', 'Event' )
    for copy in EventInfoBackup.objects.all():
        event = EventBase.objects.get(
                pk = copy.event_ptr
        )
        x = EventInfo(
                event_ptr = event,
                start = event.start,
                end = event.end,
                title = event.title,
                description = event.description,
                creator = event.creator,
                created_on = event.created_on,
                updated_on = event.updated_on,
                rule = event.rule,
                end_recurring_period = event.end_recurring_period,
                calendar = event.calendar,
                color_event = event.color_event,
        )
        # for every field "field" in EventInfo:
        x.field = copy.field
        x.event_ptr = event
        x.save()
        # for every ManyToManyField "m2mField":
        # x.m2mField.set(
        #         copy.m2mField.all()
        # )
        x.save()

def copy_from_backup_reverse(apps, schema_editor):
    EventInfo = apps.get_model('your_app', 'EventInfo')
    EventInfoBackup = apps.get_model('your_app', 'EventInfoBackup')
    for x in EventInfo.objects.all():
        copy = EventInfoBackup(
                event_ptr = x.pk
                # ...for all fields "field" except ManyToManyFields...
                # field = x.field,
        )
        # for every ManyToManyField "m2mField":
        # copy.m2mField.set(
        #         x.m2mField.all()
        # )
        copy.save()
    for x in EventInfo.objects.all():
        x.delete(
                keep_parents = True
        )

class Migration(migrations.Migration):

    dependencies = [
        ('your_app', '0020_cut_foreign_key'),
        ('schedule', '0014_use_autofields_for_pk'),
    ]

    operations = [
        migrations.CreateModel(
            name='EventInfo',
            fields=[
                ('event_ptr', models.OneToOneField(on_delete=django.db.models.deletion.CASCADE, parent_link=True, primary_key=True, related_name='event_info', serialize=False, to='schedule.event')),
                # ...other fields in EventInfo...
            ],
            bases=('schedule.event',),
        ),
        # Copy EventInfos from backup
        migrations.RunPython(
            code = copy_from_backup,
            reverse_code = copy_from_backup_reverse
        ),
        migrations.DeleteModel(
            name='EventInfoBackup',
        ),
    ]

[llazzaro]

Thanks for providing that information! I’m closing this issue. I will take a look to the open PR.