import base64
from django.db import models


class Foo(models.Model):
    _data = models.TextField(db_column='data', blank=True)

def set_data(self, data):
    self._data = base64.encodestring(data)

def get_data(self):
    return base64.decodestring(self._data)
data = property(get_data, set_data)
Поле модели Django Blob