Django ORM 的 update_or_create
官网的手写版如下：
defaults = {'first_name': 'Bob'}
try:
obj = Person.objects.get(first_name='John', last_name='Lennon')
for key, value in defaults.items():
setattr(obj, key, value)
obj.save()
except Person.DoesNotExist:
new_values = {'first_name': 'John', 'last_name': 'Lennon'}
new_values.update(defaults)
obj = Person(**new_values)
obj.save()
官网的更新版如下：
obj, created = Person.objects.update_or_create(
first_name='John', last_name='Lennon',
defaults={'first_name': 'Bob'},
)
