优化 ndb 中两个属性的不等式查询 [英] Optimizing a inequality query in ndb over two properties

问题描述

我正在尝试对有效日期范围进行查询

I'm trying to do a query into a range of valid dates

q = Licence.query(Licence.valid_from <= today, 
                  Licence.valid_to >= today,
                  ancestor = customer.key               
                  ).fetch(keys_only=True)

我知道 Datastore 不支持对两个属性的不等式查询.所以我这样做:

I know that Datastore doesn't support inequality queries over two propperties. So I do this:

kl = Licence.query(Licence.valid_from <= today, 
                  ancestor = customer.key               
                  ).fetch(keys_only=True)
licences = ndb.get_multi(kl)
for item in licences:
    if item.valid_to < today:
        licence.remove(item)

但我不喜欢，因为我认为从数据存储中检索更多我最终需要的实体(或键)时使用了太多 RAM.

But I don't like because I think that I use too much RAM retrieving more entities (or keys) from the Datastore that I finally need.

任何机构都知道进行此类查询的更好方法吗?

Any body knows a better way of doing this type of queries?

在 .get() 之前使用 .filter() 就足够了吗?

Is enough to use .filter() before .get()?

谢谢

推荐答案

一种解决方案是创建一个新字段，例如 start_week，它将查询分桶并允许您使用 IN 查询进行过滤:

One solution would be to create a new field, like start_week, which buckets the queries and allows you to use an IN query to filter:

q = Licence.query(Licence.start_week in range(5,30),
                  Licence.valid_to >= today,
                  ancestor = customer.key)

更简单:使用投影查询来识别正确的数据集，而无需获取完整的实体.这比常规查询更快.

Even simpler: Use a projection query to identify the right set of data without fetching full entities. This is faster than a regular query.

it = Licence.query(License.valid_from <= today,
                   ancestor = customer.key
                   ).iter(projection=[License.valid_to])
keys = [e.key for e in it if e.valid_to >= today]
licenses = ndb.get_multi(keys)

这篇关于优化 ndb 中两个属性的不等式查询的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！