auto_increment  differrent in  create and  create_or_get 
You should be using `PrimaryKeyField` instead of `IntegerField`. The former is auto increment, while the latter is just an arbitrary int field.

``` python
from peewee import *
from  pprint import pprint

db = SqliteDatabase('people.db')

class User(Model):
    uid = IntegerField(primary_key=True)
    name = CharField()
    password = FixedCharField()


    class Meta:
        database = db # This model uses the "people.db" database.



#db.create_tables([User])

username='xx'
try:
    user = User.get(name=username)
    #user = User.get_or_create(name=username)
    pprint(user.uid)
except:

   user=User.create(name=username,password='xx')
   print(user.uid)

```

the result is None 
by  get_or_create   the result is 1 
