Question

我正在尝试使用@JoinedColumns派生实体，

让我告诉你我的代码，

下面是sql代码，

create table TBL_EMPLOYEE_FIVE(
   EMP_ID integer ,
   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
)

这是映射实体的下面代码，

package com.entities.derived;
@Entity
@Table(name="TBL_EMPLOYEE_FIVE")
@IdClass(EmployeeId.class)
public class EmployeeOne implements Serializable{

// contructors    

@Id    
@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, setters, hashcode and equals implementation
}

这是类ID的下面代码，

@Embeddable
public class EmployeeId implements Serializable{

public EmployeeId(){}

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

private Integer employeeId;
private String empCountry;

// getters, hashcode and equals implementation

   }

用main方法编写的代码，无需Exception即可正常工作，如下所示，

用于持久保存新员工，

private static int generateId(EntityManager em,String country)throws Exception{

    Query q = em.createQuery("select max(e.employeeId) from EmployeeOne e where e.empCountry = '"+country+"'");

    List list = q.getResultList();
    int count = 0;

    if(list != null && list.size() > 0){
         count = Integer.parseInt(String.valueOf((list.get(0) != null) ? list.get(0) : "0"));
    }

    count++;
    return count;
}

插入新员工

private static void insertEmployee2(EntityManager em) throws Exception{
    EmployeeOne manager = new EmployeeOne("Rajkumar Bahadur", "NEPAL");
    manager.setEmployeeId(generateId(em, manager.getEmpCountry()));
    Set<EmployeeOne> employees = new HashSet<EmployeeOne>();  

    int count = generateId(em, "FIJI");  

    employees.add(new EmployeeOne(count,"Okajima Fahim","FIJI",manager));
    employees.add(new EmployeeOne(++count,"Jabulani Xitwo","FIJI",manager));
    manager.setEmployees(employees);
    em.persist(manager);
}

用于获取员工，

private static void getEmployees(EntityManager em) throws Exception{
    EmployeeOne manager = em.find(EmployeeOne.class, new EmployeeId(3,"CHINA"));

    Set<EmployeeOne> employees = manager.getEmployees();

    for(EmployeeOne emp : employees){

        System.out.println(emp);
    }
}

以上所有方法都运行正常。

但唯一不起作用的代码是merge，代码如下

private static void updateEmployee(EntityManager em) throws Exception{
    EmployeeOne manager = em.find(EmployeeOne.class, new EmployeeId(3,"CHINA"));          
    Set<EmployeeOne> employees = manager.getEmployees();
    int count = generateId(em, "IRAN");        
    employees.add(new EmployeeOne(count,"Zaid Khan","IRAN",manager));        
    employees.add(new EmployeeOne(++count,"Maqbool Ansari","IRAN",manager));        

    em.merge(manager);
}

我得到的例外是，

javax.persistence.EntityNotFoundException: Unable to find com.entities.derived.EmployeeOne with id com.entities.derived.EmployeeId@226b19
    at org.hibernate.ejb.Ejb3Configuration$Ejb3EntityNotFoundDelegate.handleEntityNotFound(Ejb3Configuration.java:155)
at org.hibernate.event.internal.DefaultLoadEventListener.load(DefaultLoadEventListener.java:210)
at org.hibernate.event.internal.DefaultLoadEventListener.proxyOrLoad(DefaultLoadEventListener.java:251)
at org.hibernate.event.internal.DefaultLoadEventListener.onLoad(DefaultLoadEventListener.java:148)
....

你能告诉我我哪里出错吗

Answer 1

更改

@ManyToOne( cascade= {CascadeType.PERSIST, CascadeType.PERSIST},
            fetch= FetchType.LAZY,
            targetEntity=EmployeeOne.class)

要

@ManyToOne( cascade= {CascadeType.PERSIST, CascadeType.MERGE},
            fetch= FetchType.LAZY,
            targetEntity=EmployeeOne.class)

当父级“更新”（合并）时，您需要级联EmployeeOne实例的创建。通过更改@ManyToOne注释以包含CascadeType.MERGE，您应该实现此目的。

无法将实体与派生实体合并

1 个答案: