官网的手写版如下：
update_or_create(defaults=None, **kwargs)¶
A convenience method for updating an object with the given kwargs, creating a new one if necessary. The defaults is a dictionary of (field, value) pairs used to update the object. The values in defaults can be callables.
Returns a tuple of (object, created), where object is the created or updated object and created is a boolean specifying whether a new object was created.
The update_or_create method tries to fetch an object from database based on the given kwargs. If a match is found, it updates the fields passed in the defaults dictionary.
This is meant as a shortcut to boilerplatish code. For example:
大致意思是创建或者更新，当过滤条件匹配到查询结果则将更新defaults字典中的字段，否则创建一条记录，字段内容为defaults字段中的内容。
返回（对象，已创建）的元组，其中object是已创建或已更新的对象，created是一个布尔值，指定是否创建了新对象。
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()
以上的方法使用update_or_create实现
obj, created = Person.objects.update_or_create( first_name='John', last_name='Lennon', defaults={'first_name': 'Bob'}, )
