Spring Data JPA 如何使用 Kotlin nulls 而不是 Optional [英] Spring Data JPA How to use Kotlin nulls instead of Optional
问题描述
我正在用 Spring Data JPA 和 Kotlin 编写一个 Spring Boot 应用程序,我注意到在 CrudRepository
中有以下方法:
I'm writing a Spring Boot app with Spring Data JPA and Kotlin, and I've noticed that in CrudRepository
there is the following method:
Optional<T> findById(ID id);
不过,我使用的是 Kotlin,它比 Optional
具有更流畅的处理空值的方式.有谁知道我将如何将该方法转换为这样的工作?
I'm using Kotlin, though, which has much more fluent ways of dealing with nulls than Optional
. Does anyone know how I would convert that method to work like this?
fun findById(id: ID): T?
当我扩展 Repository
本身并使用该签名创建一个存储库时,我收到错误:
When I extend Repository
itself and create a repo with that signature I get the error:
java.lang.ClassCastException: java.util.Optional cannot be cast to com.books.Book
推荐答案
从 Spring Data Lovelace SR4/Spring Boot 2.1.2 开始,一个 CrudRepository.findByIdOrNull(id: ID): T?= findById(id).orElse(null)
Kotlin 扩展现在提供了一种开箱即用的方法来检索 Spring Data 中的可为空实体.
As of Spring Data Lovelace SR4 / Spring Boot 2.1.2, a CrudRepository.findByIdOrNull(id: ID): T? = findById(id).orElse(null)
Kotlin extension now provides out of the box a way to retrieve nullable entities in Spring Data.
如果出于性能原因您想避免使用 Optional<T>
包装器,请注意您还可以使用 findFooById(id:ID): T?
函数.查询执行是特定于存储的,但大多数都使用内部可空值,并且将避免 Optional
包装器的成本.请注意,对于大多数用例,此开销应该可以忽略不计,因此建议使用内置扩展.
If for performance reasons you would like to avoid the usage of Optional<T>
wrapper, be aware that you have also the possibility to create a custom interface with a findFooById(id: ID): T?
function. Query execution is store specific, but and most are using internally nullable values and will avoid the cost of Optional<T>
wrapper. Notice this overhead should be negligible for most use cases, so using the builtin extension is recommended method.
有关详细信息,请参阅 DATACMNS-1346.
See DATACMNS-1346 for more details.
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