Question

这是我的sql表结构：

create table TBL_EMPLOYEE_FIVE(
    EMP_ID integer generated always as identity(start with 50, increment by 4),
    NAME varchar(50),
    COUNTRY varchar(50),
    MGR_ID integer,
    MGR_COUNTRY varchar(50),
    constraint PK_COMPOSIT_001AD primary key(EMP_ID,COUNTRY),
    constraint  FK_COMPO_00123 foreign key(MGR_ID,MGR_COUNTRY) references TBL_EMPLOYEE_FIVE
)

这是我的实体映射：

@Entity
@Table(name="TBL_EMPLOYEE_FIVE")
@IdClass(EmployeeId.class)
public class EmployeeOne implements Serializable{

    public EmployeeOne(){}
    public EmployeeOne(String employeeName,String empCountry){
        this.empCountry = empCountry;
        this.employeeName = employeeName;
    }

    public EmployeeOne(String employeeName,String empCountry,EmployeeOne manager){
        this.empCountry = empCountry;
        this.employeeName = employeeName;
        this.manager = manager;
    }

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="EMP_ID")
    private Integer employeeId;

    @Id
    @Column(name="COUNTRY")
    private String empCountry;

    @Column(name="NAME")
    private String employeeName;

    @ManyToOne( cascade= {CascadeType.PERSIST, CascadeType.PERSIST},
            fetch= FetchType.LAZY,
            targetEntity=EmployeeOne.class)
            @JoinColumns({
            @JoinColumn(name="MGR_ID",referencedColumnName="EMP_ID"),
            @JoinColumn(name="MGR_COUNTRY",referencedColumnName="COUNTRY")
    })
    private EmployeeOne manager;

    @OneToMany(cascade={CascadeType.PERSIST, CascadeType.PERSIST},mappedBy="manager")
    private Set<EmployeeOne> employees;
// getters and setters,
}

这是嵌入式id映射，

@Embeddable
public class EmployeeId implements Serializable{

    public EmployeeId(){}

    public EmployeeId(Integer employeeId,String empCountry){
       this.employeeId = employeeId;
       this.empCountry = empCountry;
    }

    @Column(name="EMP_ID")
    private Integer employeeId;

    @Column(name="COUNTRY")
    private String empCountry;
// only getters and implementation of hashcode and equals method
}

这就是我试图在我的主要方法中运行的内容：

EmployeeOne manager = new EmployeeOne("Yousuf Ahmadinejad", "IRAN");
em.persist(manager);

但在这里，我得到一个例外，即

Caused by: javax.persistence.PersistenceException: org.hibernate.exception.SQLGrammarException: Attempt to modify an identity column 'EMP_ID'.

这不像我没有理解异常，

但为什么这个例外发生在第一位？我已经使用@GenerateValue为Empid注释了它，我没有手动设置empId。是否发生此异常是因为我将主键组合为empId和country，而empId是使用Identity自动生成的，因此它给出了异常？

你能告诉我哪里出错了

我想在这里添加的另一件事是，如果我删除了EmployeeId.java的@Column和@Embeddeble注释，而不是运行，我会得到以下异常，

Caused by: org.hibernate.PropertyAccessException: could not set a field value by reflection setter of com.entities.derived.EmployeeId.employeeId

所以只是试图找到解决方案来坚持员工保持自动生成的ID，因为它是

Answer 1

首先，Hibernate不为复合键生成id，因此您应该将EmployeeOne更改为：

@Id
//@GeneratedValue(strategy=GenerationType.IDENTITY) remove this line
@Column(name="EMP_ID")
private Integer employeeId;

其次，不是你应该如何实现EmployeeId复合密钥类。请参阅：https://stackoverflow.com/a/3588400/1981720

第三，数据库抛出异常，而不是Hibernate。检查您是否与另一个数据库获得了相同的异常。

使用@JoinedColumns尝试派生标识符，得到错误尝试修改标识列

1 个答案: