n_property
n + 1 = 2
用法：
n_property:
from n_property import n_class, n_property
@n_class
class Review(object):
subject = n_property(fallback=None)
@subject.n_getter
@classmethod
def get_subjects(cls, insts):
subject_ids = [inst.subject_id for inst in insts]
return Subject.gets(subject_ids, filter_none=False)
reviews = Review.gets(review_ids)
print reviews[0].subject # 第1次 Subject.gets 请求
print [r.subject for r in reviews] # 触发批量prefetch，第2次 Subject.gets 请求n_method (一般预期的 method 具有状态，被cache之后更容易产生不符合预期的情况，请尽量使用n_property):
@n_class
class Review(object):
@n_method(implement='get_subjects')
def get_subject(self, user_id=''):
return None
@classmethod
def get_subjects(cls, insts, user_id=''):
subject_ids = [inst.subject_id for inst in insts]
return Subject.gets(subject_ids, filter_none=False, user_id=user_id)
print reviews[0].get_subject(user_id='') # 第1次 Subject.gets 请求
print [r.get_subject(user_id='') for r in reviews] # 触发批量prefetch，第2次 Subject.gets 请求如果是Python3，则不需要加 @n_class 装饰器
