为什么，而不是被修改，数据被添加为新行？

Question

我正在使用Peewee for Python并尝试更新实例的名称，但不是更新实例，而是将其添加为新实例。有什么问题？

from peewee import *
from datetime import date
db=SqliteDatabase('people.db')

class Person(Model):
    name=CharField()
    birthday=DateField()
    is_relative=BooleanField()

    class Meta:
        database=db

class Pet(Model):
    owner=ForeignKeyField(Person,related_name='pets')
    name=CharField()
    animal_type=CharField()

    class Meta:
        database=db


db.connect()

db.create_tables([Person,Pet],safe=True)

uncle_bob=Person(name='Bob',birthday=date(1960,1,15),is_relative=True)
uncle_bob.save()

grandma = Person.create(name='Grandma', birthday=date(1935, 3, 1), is_relative=True)
herb = Person.create(name='Herb', birthday=date(1950, 5, 5), is_relative=False)
grandma.name='Grand Dadi'
grandma.save()

我得到下表：

1|Bob|1960-01-15|1
2|Grandma|1935-03-01|1
3|Herb|1950-05-05|0
4|Bob|1960-01-15|1
5|Grand Dadi|1935-03-01|1
6|Herb|1950-05-05|0