text: from django.db import models
  
  class ReferencedEthereumObject(models.Model):
      reference = models.CharField(max_length=190, db_index=True, unique=True)
      order = models.ForeignKey('pretixbase.Order', on_delete=models.CASCADE)
      payment = models.ForeignKey('pretixbase.OrderPayment', null=True, blank=True, on_delete=models.CASCADE)
  