Question

我有两个实体如下：

@Entity
@Table(name = "tax")
public class TaxReturn {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long id;
    @Column(name = "period")
    private String fillingPeriod;
    @Column(name = "created_date")
    private LocalDateTime dateCreated;
    @Column(name = "total_tax")
    private int totalTax;
    @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
    @JoinColumn(name = "tax_id", nullable = false)
    private List<Employee> employees;
}

@Entity
@Table(name = "emp")
public class Employee {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    @Column(name = "other_name")
    private String firstName;
    @Column(name = "surname")
    private String lastName;
    @Column(name = "tax_amount")
    private int taxAmount;
}

上述信息代表一份回报，其中包含一份员工名单，说明已缴纳多少税款。退货实体包含所有员工的总金额。我需要在HQL中编写一个查询，该查询将使用返回ID和员工ID检索员工。下面是我写的，但我收到一个错误，因为它没有生成正确的mysql。

session.getTransaction().begin();
Long taxReturnId = 5L;
Long empId = 4L;
Query query = session.createQuery("select p.employees from TaxReturn p left join Employee e where p.id = '5' and e.id = '4'");
List<Employee> employeeList = query.list();
System.out.println(employeeList.get(0).toString());
session.getTransaction().commit();

这是正确的查询吗？

谢谢，阿什利

Answer 1

查询应为：

select p.employees from TaxReturn p left join p.employees e where p.id = '5' and e.id = '4'

N.B。连接部分与您的不同，因为您必须在连接时指定映射关系的字段。

您也可以返回TaxReturn并从那里获得List的{{1}}：

Employee

另外，我注意到你以非传统的方式绘制了关系通常单向映射在Query query = session.createQuery("select p from TaxReturn p left join p.employees e where p.id = '5' and e.id = '4'"); List<Employee> employeeList = query.singleResult().getEmployees();侧完成，而不是相反。还有一些与性能相关的问题，请查看此Article了解更多详情

带连接的hibernate查询

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