# models.py
from django.db import models
from seal.models import SealableModel

class Location(SealableModel):
    latitude = models.FloatField()
    longitude = models.FloatField()

class SeaLion(SealableModel):
    height = models.PositiveIntegerField()
    weight = models.PositiveIntegerField()
    location = models.ForeignKey(Location, models.CASCADE, null=True)
    previous_locations = models.ManyToManyField(Location, related_name='previous_visitors')

>>> import warnings
>>> from seal.exceptions import UnsealedAttributeAccess
>>> warnings.filterwarnings('error', category=UnsealedAttributeAccess)
>>> location = Location.objects.create(latitude=51.585474, longitude=156.634331)
>>> sealion = SeaLion.objects.create(height=1, weight=100, location=cls.location)
>>> sealion.previous_locations.add(cls.location)
>>> SeaLion.objects.only('height').seal().get().weight
Traceback (most recent call last)
...
SealedObject: Cannot fetch deferred field weight on sealed SeaLion object.
>>> SeaLion.objects.seal().get().location
Traceback (most recent call last)
...
UnsealedAttributeAccess: Cannot fetch related field location on sealed SeaLion object.
>>> SeaLion.objects.seal().get().previous_locations.all()
Traceback (most recent call last)
...
UnsealedAttributeAccess: Cannot fetch many-to-many field previous_locations on sealed SeaLion object.