# Tabela domain
MariaDB [opensips]> desc domain;
+---------------+------------------+------+-----+---------------------+----------------+
| Field         | Type             | Null | Key | Default             | Extra          |
+---------------+------------------+------+-----+---------------------+----------------+
| id            | int(10) unsigned | NO   | PRI | NULL                | auto_increment |
| domain        | char(64)         | NO   | UNI |                     |                |
| attrs         | char(255)        | YES  |     | NULL                |                |
| created_at    | datetime         | YES  |     | NULL                |                |
| last_modified | datetime         | NO   |     | 1900-01-01 00:00:01 |                |
+---------------+------------------+------+-----+---------------------+----------------+

MariaDB [opensips]> desc subscriber;
+---------------+------------------+------+-----+---------+----------------+
| Field         | Type             | Null | Key | Default | Extra          |
+---------------+------------------+------+-----+---------+----------------+
| id            | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| username      | char(64)         | NO   | MUL |         |                |
| domain        | char(64)         | NO   |     |         |                |
| password      | char(25)         | NO   |     |         |                |
| email_address | char(64)         | NO   |     |         |                |
| ha1           | char(64)         | NO   |     |         |                |
| ha1b          | char(64)         | NO   |     |         |                |
| rpid          | char(64)         | YES  |     | NULL    |                |
+---------------+------------------+------+-----+---------+----------------+
8 rows in set (0.001 sec)


...


import hashlib

from django.db import models


class Domain(models.Model):
    """Model user to abstract 'domain' table."""
    domain = models.CharField(unique=True, max_length=64)
    attrs = models.CharField(max_length=255, blank=True, null=True)
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(db_column='last_modified', auto_now=True)

    class Meta:
        app_label = 'api'
        db_table = 'domain'
        ordering = ['domain']
        verbose_name = 'domain'
        verbose_name_plural = 'domains'


class Subscriber(models.Model):
    """Model user to abstract 'subscriber' table."""
    username = models.CharField(max_length=64)
    domain = models.ForeignKey(
        'Domain',
        on_delete=models.CASCADE,
        to_field='domain',
        related_name='domain'
    )
    email = models.CharField(db_column='email_address', max_length=64)
    rpid = models.CharField(max_length=64, blank=True, null=True)

    _password = models.CharField(db_column='password', max_length=25)
    _ha1 = models.CharField(db_column='ha1', max_length=64)
    _ha1b = models.CharField(db_column='ha1b', max_length=64)

    class Meta:
        app_label = 'api'
        db_table = 'subscriber'
        verbose_name = 'subscriber'
        ordering = ['username', 'domain']
        verbose_name_plural = 'subscribers'
        unique_together = [['username', 'domain']]

    @property
    def password(self, value):
        """Property to automatize an hash generation of password."""
        self._password = value
        md5 = lambda x: hashlib.md5(str(x).encode('utf-8')).hexdigest()
        self._ha1 = md5('%s:%s:%s' % (self.username, self.domain, value))
        self._ha1b = md5('%s@%s:%s:%s' % (self.username, self.domain, self.domain, value))


ERRO:
api.Subscriber.domain: (fields.E302) Reverse accessor for 'Subscriber.domain' clashes with field name 'Domain.domain'.
	HINT: Rename field 'Domain.domain', or add/change a related_name argument to the definition for field 'Subscriber.domain'.
api.Subscriber.domain: (fields.E303) Reverse query name for 'Subscriber.domain' clashes with field name 'Domain.domain'.
	HINT: Rename field 'Domain.domain', or add/change a related_name argument to the definition for field 'Subscriber.domain'.