如何在数据存储区(AppEngine)中随机获取某些内容? [英] How to get something random in datastore (AppEngine)?
问题描述
images = Image.all()
count = images .count()
random_numb = random.randrange(1,count)
image = Image.get_by_id(random_numb)
但事实证明,AppEngine上的数据存储区中的id不是从1开始的。
我在数据存储区中有两个图像,它们的id分别是6001和7001。
有没有更好的方法来检索随机图像? 解决方案
数据存储是分布式的,因此ID是非顺序的:两个数据存储节点需要能够同时生成一个ID而不会造成冲突。
要获得一个随机实体,您可以在创建时将0和1之间的随机float添加到每个实体。然后查询,做这样的事情:
rand_num = random.random()
entity = MyModel.all ).order('rand_num')。filter('rand_num> =',rand_num).get()
如果实体是None:
entity = MyModel.all()。order('rand_num' ).get()
编辑:建议。
Currently i'm using something like this:
images = Image.all()
count = images.count()
random_numb = random.randrange(1, count)
image = Image.get_by_id(random_numb)
But it turns out that the ids in the datastore on AppEngine don't start from 1. I have two images in datastore and their ids are 6001 and 7001.
Is there a better way to retrieve random images?
The datastore is distributed, so IDs are non-sequential: two datastore nodes need to be able to generate an ID at the same time without causing a conflict.
To get a random entity, you can attach a random float between 0 and 1 to each entity on create. Then to query, do something like this:
rand_num = random.random()
entity = MyModel.all().order('rand_num').filter('rand_num >=', rand_num).get()
if entity is None:
entity = MyModel.all().order('rand_num').get()
Edit: Updated fall-through case per Nick's suggestion.
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