"Foreign Keys" across very separate databases in Django - django

Question

I've writing a Django site that uses two different databases. One is the local, let's call it, "Django", database that stores all of the standard tables from a pretty standard install -- auth, sites, comments, etc. -- plus a few extra tables.
Most of the data, including users, comes from a database on another server, let's call it the "Legacy" database.
I'm looking for suggestions on clean, pythonic ways of connecting the two databases, particularly in regards to users.
I'm using a proxy model, which works great when I can explicitly use it, but I run into problems when I'm accessing the user object as a related object (for example, when using the built-in django comments system).
Here's what the code looks like:
models.py: (points to the Django database)
from django.db import models
from django.conf import settings
from django.contrib.auth.models import User as AuthUser, UserManager as AuthUserManager, AnonymousUser as AuthAnonymousUser
class UserPerson(models.Model):
user = models.OneToOneField(AuthUser, related_name="person")
person_id = models.PositiveIntegerField(verbose_name='Legacy ID')
def __unicode__(self):
return "%s" % self.get_person()
def get_person(self):
if not hasattr(self, '_person'):
from legacy_models import Person
from utils import get_person_model
Person = get_person_model() or Person
self._person = Person.objects.get(pk=self.person_id)
return self._person
person=property(get_person)
class UserManager(AuthUserManager):
def get_for_id(self, id):
return self.get(person__person_id=id)
def get_for_email(self, email):
try:
person = Person.objects.get(email=email)
return self.get_for_id(person.pk)
except Person.DoesNotExist:
return User.DoesNotExist
def create_user(self, username, email, password=None, *args, **kwargs):
user = super(UserManager,self).create_user(username, email, password, *args, **kwargs)
try:
person_id = Person.objects.get(email=email).pk
userperson, created = UserPerson.objects.get_or_create(user=user, person_id=person_id)
except Person.DoesNotExist:
pass
return user
class AnonymousUser(AuthAnonymousUser):
class Meta:
proxy = True
class User(AuthUser):
class Meta:
proxy=True
def get_profile(self):
"""
Returns the Person record from the legacy database
"""
if not hasattr(self, '_profile_cache'):
self._profile_cache = UserPerson.objects.get(user=self).person
return self._profile_cache
objects = UserManager()
legacy_models.py: (points to the "Legacy" database)
class Person(models.Model):
id = models.AutoField(primary_key=True, db_column='PeopleID') # Field name made lowercase.
code = models.CharField(max_length=40, blank=True, db_column="person_code", unique=True)
first_name = models.CharField(max_length=50, db_column='firstName', blank=True) # Field name made lowercase.
last_name = models.CharField(max_length=50, db_column='lastName', blank=True) # Field name made lowercase.
email = models.CharField(max_length=255, blank=True)
def __unicode__(self):
return "%s %s" % (self.first_name, self.last_name)
def get_user(self):
from models import User
if not hasattr(self,'_user'):
self._user = User.objects.get_for_id(self.pk)
return self._user
user = property(get_user)
class Meta:
db_table = u'People'
I've also whipped up my own middleware, so request.user is the proxy User object also.
The real problem is when I'm using something that has user as a related object, particularly in a template where I have even less control.
In the template:
{{ request.user.get_profile }}
{# this works and returns the related Person object for the user #}
{% for comment in comments %} {# retrieved using the built-in comments app %}
{{ comment.user.get_profile }}
{# this throws an error because AUTH_PROFILE_MODULE is not defined by design #}
{% endfor %}
Short of creating a wrapped version of the comments system which uses my proxy User model instead, is there anything else I can do?

Answer 1

Here's how I resolved it. I stopped using the User proxy altogether.
models.py:
from django.db import models
from legacy_models import Person
from django.contrib.auth.models import User
class UserPerson(models.Model):
user = models.OneToOneField(User, related_name="person")
person_id = models.PositiveIntegerField(verbose_name='PeopleID', help_text='ID in the Legacy Login system.')
def __unicode__(self):
return "%s" % self.get_person()
def get_person(self):
if not hasattr(self, '_person'):
self._person = Person.objects.get(pk=self.person_id)
return self._person
person=property(get_person)
class LegacyPersonQuerySet(models.query.QuerySet):
def get(self, *args, **kwargs):
person_id = UserPerson.objects.get(*args, **kwargs).person_id
return LegacyPerson.objects.get(pk=person_id)
class LegacyPersonManager(models.Manager):
def get_query_set(self, *args, **kwargs):
return LegacyPersonQuerySet(*args, **kwargs)
class LegacyPerson(Person):
objects = LegacyPersonManager()
class Meta:
proxy=True
and legacy_models.py:
class Person(models.Model):
id = models.AutoField(primary_key=True, db_column='PeopleID') # Field name made lowercase.
code = models.CharField(max_length=40, blank=True, db_column="person_code", unique=True)
first_name = models.CharField(max_length=50, db_column='firstName', blank=True) # Field name made lowercase.
last_name = models.CharField(max_length=50, db_column='lastName', blank=True) # Field name made lowercase.
email = models.CharField(max_length=255, blank=True)
def __unicode__(self):
return "%s %s" % (self.first_name, self.last_name)
def get_user(self):
from models import User
if not hasattr(self,'_user'):
self._user = User.objects.get_for_id(self.pk)
return self._user
def set_user(self, user=None):
self._user=user
user = property(get_user, set_user)
class Meta:
db_table = u'People'
Finally, in settings.py:
AUTH_PROFILE_MODULE = 'myauth.LegacyPerson'
This is a simpler solution, but at least it works! It does mean that whenever I want the legacy record I have to call user_profile, and it means that there's an additional query for each user record, but this is a fair trade-off because actually it isn't very likely that I will be doing a cross check that often.