Django QuerySet API

 https://docs.djangoproject.com/en/2.1/ref/models/querysets/

update_or_create

update_or_create(defaults=None, **kwargs)
根据kwargs去数据库中查询,其实就是过滤，如果不填，相当于拿所有数据（多个kwargs之间是and的关系）
如果查到：用defaults去更新
查不到：用default和kwargs创建（对于两者间相同的字段，default会覆盖kwargs）

    def update_or_create(self, defaults=None, **kwargs):
        """
        Looks up an object with the given kwargs, updating one with defaults
        if it exists, otherwise creates a new one.
        Returns a tuple (object, created), where created is a boolean
        specifying whether an object was created.