java - JPA CascadeType.PERSIST 是如何工作的？

Question

在我的示例中，Employee 与 Department 具有CascadeType.PERSIST 的OneToOne 关系。当我坚持多个 Employee,

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为什么 EntityManager 为所有 Employee 记录保留一个 Department 记录？

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我的期望是，如果我们使用 CascadeType.PERSIST，当一个 Employee 被持久化时，一个 Department 记录将被重新创建每个 Employee 记录。

员工.java

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

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}

部门.java

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

测试.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。

更改您的代码以使其正确，

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