JPA CascadeType.PERSIST如何工作？

java jpa

2022-09-02 10:40:44

在我的示例中，与有关系。当我坚持多个，EmployeeOneToOneDepartmentCascadeType.PERSISTEmployee

为什么为所有记录保留一条记录？EntityManagerDepartmentEmployee

我的期望是，如果我们使用，当一个被持久化时，将为每个记录重新创建一个记录。CascadeType.PERSISTEmployeeDepartmentEmployee

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;

    -----
}

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

答案 1

JPA 维护对象标识，并且不会保留现有对象。

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);
}

答案 2