# -*- coding: utf-8 -*-
from peewee import *
db = SqliteDatabase('temp\\temp.db')
class Cathegory(Model):
    id = IntegerField(primary_key=True)
    name = CharField(max_length=20)
    class Meta:
        database = db
class Assortiment(Model):
    id = IntegerField(primary_key=True)
    name = CharField(max_length=40)
    cathegory = ForeignKeyField(Cathegory, related_name='goods', null=True)
    class Meta:
        database = db
Cathegory.create_table()
Assortiment.create_table()
cath = Cathegory.create(name=u'Чай')
item = Assortiment.create(name=u'Цейлонский', cathegory=cath)

>>> print cath.name
Чай
>>> print item.name
Цейлонский
>>> print item.cathegory.name
Чай

>>> items = [x for x in Assortiment.select()]
>>> items
[<__main__.Assortiment object at 0x00E92DB0>]
>>> print items[0].name
Цейлонский
>>> print items[0].cathegory
None
>>> print items[0].cathegory.name
Traceback (most recent call last):
  File "<interactive input>", line 1, in <module>
AttributeError: 'NoneType' object has no attribute 'name'

id = IntegerField(primary_key=True)

id = PrimaryKeyField(primary_key=True)