poulpe/shared/models.py

from django.db import models
from django.utils.translation import ugettext_lazy as _


class EventSpecificMixin(models.Model):
    """Mixin allowing for event-specific models instances
    or not (depending on whether the event field is null)"""

    event = models.ForeignKey(
        'event.Event',
        verbose_name=_("évènement"),
        help_text=_("Si spécifié, l'instance du modèle"
                    "est spécifique à l'évènement en question"),
        blank=True,
        null=True
    )

    class Meta:
        abstract = True