transfer_partnership.py

from django.db import models


class TransferPartnershipManager(models.Manager):

    def get_by_natural_key(self, from_name, to_name):
        return self.get(
            from_organization__name=from_name,
            to_organization__name=to_name)

class Organization(models.Model):
  ...
  transfer_partners = models.ManyToManyField(
      'self', through='user_accounts.TransferPartnership',
      symmetrical=False, blank=True,
      related_name='related_transfer_partners+')
 

class TransferPartnership(models.Model):

    from_organization = models.ForeignKey(
        'user_accounts.Organization', on_delete=models.PROTECT,
        related_name='transfer_partnerships_out')
    to_organization = models.ForeignKey(
        'user_accounts.Organization', on_delete=models.PROTECT,
        related_name='transfer_partnerships_in')

    def __str__(self):
        return "{} and {}".format(
            self.from_organization.name, self.to_organization.name)

    def natural_key(self):
        return (self.from_organization.name, self.to_organization.name)

    class Meta:
        unique_together = ('from_organization', 'to_organization')