How does the JPA CascadeType.PERSIST work ?

Question

In my example, Employee has an OneToOne relationship to Department with CascadeType.PERSIST. When I persist multiple Employee,

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Why does the EntityManager persist a single Department record for all Employee records?

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My expectation is, if we use CascadeType.PERSIST, when an Employee is being persisted, a Department record will be created anew for each Employee record.

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;

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}

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();
}

Result :

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 maintains object identity and will not persist an existing object.

Change you code to be correct,

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