JPA CascadeType.PERSIST如何工作？

Question

在我的例子,Employee有一个OneToOne以关系Department与CascadeType.PERSIST.当我坚持多次Employee,

---

为什么EntityManager持续Department记录所有Employee记录？

---

我的期望是,如果我们使用CascadeType.PERSIST,当一个Employee被持久化时,Department将为每个Employee记录重新创建一条记录.

Employee.java

@Entity
public class Employee {
    private String id;
    private String name;
    @OneToOne(cascade = CascadeType.PERSIST)
    @JoinColumn(name = "DEP_ID", referencedColumnName = "ID")
    private Department department;

    -----
}

Department.java

@Entity
public class Department implements Serializable {
    private String id;
    private String name;
}

Test.java

public void insert() {
    em = emf.createEntityManager();
    em.getTransaction().begin();
    Department department = new Department("Test Department");
    for(int i=1; i <= 10; i++) {
        Employee e = new Employee("EMP" + i, department);
        em.persist(e);
    }
    em.getTransaction().commit();
    em.close();
}

结果:

Employee Table          Department Table
=================       ==============================
ID  Name  DEP_ID        ID      NAME    
=================       ==============================
1   EMP1    1           1       Test Department
2   EMP2    1
3   EMP3    1
4   EMP4    1
5   EMP5    1
6   EMP6    1
7   EMP7    1
8   EMP8    1
9   EMP9    1
10  EMP10   1   

Answer 1

JPA维护对象标识,不会保留现有对象.

将代码更改为正确,

for(int i=1; i <= 10; i++) {
    Department department = new Department("Test Department");
    Employee e = new Employee("EMP" + i, department);
    em.persist(e);
}