英文:
Google App Engine datastore for Go does not have != filter
问题
最近我在使用 GAE 的 go 语言版本，并发现它的数据存储 API 中缺少基本的 "!="（不等于）过滤器。
https://developers.google.com/appengine/docs/go/datastore/queries#Go_Property_filters
它也没有 "OR" 条件操作符。
有人可以告诉我如何筛选不等于某个值的数据吗？
英文:
I am messing with GAE for go recently and found it misses fundamental != (not equal to) filter in their datastore API.
https://developers.google.com/appengine/docs/go/datastore/queries#Go_Property_filters
It also has no "OR" condition operand.
Could anyone tell me how could I filter data which is not equal to something?
答案1
得分: 6
即使那些具有"!="过滤器的语言实际上也将其分解为两个不等式过滤器（一个大于号和一个小于号）。也许采取相同的方法可以解决你的问题？
select * from table where param != "test"
等同于
select * from table where param > "test"
再与
select * from table where param < "test"
的结果合并
虽然不是理想的解决方案，但考虑到平台的限制...我认为这是你唯一的选择。
英文:
even the languages that DO have the "!=" filter actually break it down into two inequality filters (one > and one <). Maybe doing the equivalent will solve your problem?
>select * from table where param != "test"
becomes equal to
>select * from table where param > "test"
merged with the results of
>select * from table where param < "test"
not ideal, but given the limitations of the platform... I think it's your only choice.
答案2
得分: 3
从你提供的链接页面上，实际上有一个如何执行这种查询的示例。
从查询限制中：
> 不等式过滤器仅限于一个属性
>
>>为了避免扫描整个索引表，查询机制依赖于查询的所有潜在结果在索引中相邻。为了满足这个约束条件，单个查询不能在所有过滤器中对多个属性使用不等式比较符（<，<=，>，>=）。例如，以下查询是有效的，因为两个不等式过滤器都应用于同一个属性：
q := datastore.NewQuery("Person").
Filter("BirthYear >=", minBirthYear).
Filter("BirthYear <=", maxBirthYear)
英文:
From the page you linked there's actually an example of how to do that kind of queries.
From Restrictions on queries:
> Inequality filters are limited to at most one property
>
>>To avoid having to scan the entire index table, the query mechanism relies on all of a query's potential results being adjacent to one another in the index. To satisfy this constraint, a single query may not use inequality comparisons (<, <=, >, >=) on more than one property across all of its filters. For example, the following query is valid, because both inequality filters apply to the same property:
q := datastore.NewQuery("Person").
Filter("BirthYear >=", minBirthYear).
Filter("BirthYear <=", maxBirthYear)
通过集体智慧和协作来改善编程学习和解决问题的方式。致力于成为全球开发者共同参与的知识库，让每个人都能够通过互相帮助和分享经验来进步。
评论