get_or_create

Article.objects.update_or_create() ？

@wuwukai007 请问，这种分装好的底层又是怎么实现的呢？

1 比较符合 Python 哲学

@wuwukai007
我看它文档里面还真是 try 出来的，真原始啊

应该用 try except 结构，避免判断
参考 Python 官方文档 https://docs.python.org/3.6/glossary.html#term-eafp

@Phishion try 就避免了很多条件判断，写 Python 本身就是为了快速开发嘛

@zeroDev 好的 我瞧瞧

@zeroDev 我一直潜意识认为报错会有额外的性能开销，所以就感觉用 try 处理正常业务逻辑很奇怪

你可以这样理解，如果存在的可能新远远大于 不存在，那么使用 try 的性能不就会搞的多吗，不用 try，每次都要判断

@wuwukai007 有道理，谢谢！

文档如是说：
update_or_create()
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:

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()
This pattern gets quite unwieldy as the number of fields in a model goes up. The above example can be rewritten using update_or_create() like so:

obj, created = Person.objects.update_or_create(
first_name='John', last_name='Lennon',
defaults={'first_name': 'Bob'},
)
For detailed description how names passed in kwargs are resolved see get_or_create().

As described above in get_or_create(), this method is prone to a race-condition which can result in multiple rows being inserted simultaneously if uniqueness is not enforced at the database level.

Like get_or_create() and create(), if you’re using manually specified primary keys and an object needs to be created but the key already exists in the database, an IntegrityError is raised.

我用这样,不知道性能好不好
article = Article.objects.filter(id=9999).first()
if(article):

@lixuda 我觉得用它封装好的性能最好，判断太多代码也显得不整洁

@Phishion 看错了，是更新逻辑，update_or_create

有的数据库支持 upsert

你看源码,其实这俩逻辑差不多. get 里面就是 filter + try catch

你的方法 2 会引发两次查询，优化文档经常提到不要滥用 exists()：如果后续仍需要使用到对象数据，就无须用 exists()去判断对象存在与否。

用 #13 的方法也可以。

@nonduality
@chaleaoch
@lixuda
感谢提供指导！