When is it recommended to use custom migrations instead of standard database migration procedures?

It is recommended to use custom database migrations in the following cases:

• When standard migration tools do not support the required operations (e.g., complex schema changes that cannot be expressed declaratively).
• When additional actions are needed during migration, such as data transformation, running scripts, or integrating with external systems.
• If more fine-grained control over the order and content of migrations is required.

For example, in Django, you can create custom migrations using RunPython to execute custom code:

from django.db import migrations

def forwards_func(apps, schema_editor):
    MyModel = apps.get_model('app_name', 'MyModel')
    for obj in MyModel.objects.all():
        obj.field = transform(obj.field)
        obj.save()

class Migration(migrations.Migration):
    dependencies = [('app_name', '0001_initial')]
    operations = [migrations.RunPython(forwards_func)]

Thus, custom migrations provide flexibility when working with database changes that are not covered by standard tools.