使用JPA检索单个值? [英] Retrieving single value using JPA?

问题描述

JPA是否支持将单个值映射到标量数据类型?例如，要在以下查询中映射NUM

Is there any support by JPA to map single values to scalar data types? For example, to map NUM in the following query

SELECT COUNT(*) AS NUM FROM EMPLOYEES

一些变量

int numerOfEmployees

还是在这种用例中必须使用JDBC?

or do I have to use JDBC for such use cases?

推荐答案

是的，您可以从JPQL查询中返回标量类型

Yes, you can return scalar types from JPQL queries

long num = ((Number)em.createQuery("select count(e) from Employee e")
                    .getSingleResult()).longValue();

以及本机SQL查询中的

as well as from native SQL queries:

long num = ((Number)em.createNativeQuery("select count(*) from Employees")
                    .getSingleResult()).longValue();

请注意，在某些情况下，结果类型可能取决于数据库，即它可能类似于BigDecimal.

Note that in some cases result type may depend on the database, i.e. it can be something like BigDecimal.

这篇关于使用JPA检索单个值?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！