java - 即使提供转换类后也出现 ClassCastException

Question

这个问题已经有答案了:

why simple select query returns List<Mymodel> but join query return List<Object> in jpa (3 个回答)

已关闭 8 年前。

我有以下代码片段，当我执行时，我得到

java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to test.hr.Employee

代码:

  Query query = 
            getEntityManager().createNamedQuery("Employee.findEmployees");
        List<Employee> result = query.getResultList();
        if (result != null) {
            for (int i = 0; i < result.size(); i++) {
                Employee emp = (Employee) result.get(i);
                log.info("Employee =" +emp.getNumber());
            }

JPQL:

select DISTINCT u.projectId,e.empNumber from Employee e LEFT JOIN  
e.userProjectsList u  JOIN u.projectMaster pm
where e.userNumber='SMITH'

如何摆脱这个异常？

Answer 1

实际上，您的查询不会返回 Employee ，而是返回一个对象数组(包含项目 id 和 Employee id 的对象数组)，因此这里您有两个选择:

1- 更改您的 JPQL 查询，如下所示:

SELECT e from Employee e

2- 或者更改代码以从对象读取:

Query query = 
        getEntityManager().createNamedQuery("Employee.findEmployees");
    List<Object[]> result = query.getResultList();
    if (result != null) {
        for (int i = 0; i < result.size(); i++) {
            Object[] emp = (Object[]) result.get(i);
            log.info("Employee =" +emp[0]);
        }

编辑:

并引用您需要做的编辑:

        for (int i = 0; i < result.size(); i++) {
            Object[] emp = (Object[]) result.get(i);
            log.info("Employee Number=" +emp[1]);
        }