JPA本机查询返回Double或BigDecimal [英] JPA native query returns Double or BigDecimal

问题描述

我有下面的简单代码:

@PersistenceContext(name = "mycontext")
private EntityManager entityManager;

public void getAggregatePower() {

    String sqlString = "SELECT SUM(power) FROM mytable";
    Object singleResult = entityManager.createNativeQuery(sqlString).getSingleResult();
    System.out.println(singleResult.getClass().getName());

}

当我在真实环境中运行此命令时，打印说明将打印java.math.BigDecimal.但是，当我在单元测试环境中运行此命令时，打印说明将打印java.lang.Double.
在这两种情况下，我都使用WildFly 9服务器和Postgresql 9.4数据库.我还使用Arquillian进行单元测试.对我来说，唯一值得注意的区别是数据库中的记录数.
mytable表中的power列是numeric(10,3).

When I run this in a real environment, the print instructions prints java.math.BigDecimal. But when I run this in my unit tests environment, the print instructions prints java.lang.Double.
In both cases I use a WildFly 9 server and a Postgresql 9.4 database. I also use Arquillian for unit tests. For me, the only noticeable difference is the number of records in database.
The power column in mytable table is a numeric(10,3).

我想避免使用丑陋的代码，例如:

I would like to avoid ugly code such as:

if (singleResult instance of Double) {
    ...
} else if (singleResult instance of BigDecimal) {
    ...
}

无论我的运行环境如何，都可以始终拥有相同的实例吗?

Is there a way to always have the same instance no matter my running environment ?

推荐答案

BigDecimal和Double都扩展了Number，因此您可以执行以下操作:

Both BigDecimal and Double extend Number, so you can do:

Number singleResult = ((Number) entityManager.createNativeQuery(sqlString).getSingleResult());
double resultAsDouble = singleResult.doubleValue();
BigDecimal resultAsBigDecimal = new BigDecimal(singleResult.toString()); 

如果要使用基本类型，请使用resultAsDouble，但不关心保留确切的精度，否则请使用resultAsBigDecimal.

Use resultAsDouble if you want the primitive type, but don't care about preserving the exact precision, use resultAsBigDecimal otherwise.

这篇关于JPA本机查询返回Double或BigDecimal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！