JPA-Hibernate 多对多关系映射

（1）实体类

@Entity
@Table(name = "erp_role")
public class Role {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;
    private String name;
    private String description;
    @ManyToMany
    @JoinTable(name = "erp_role_priv", joinColumns = @JoinColumn(name = "roleid"), inverseJoinColumns = @JoinColumn(name = "privid"))
    private Set<Priv> privs = new HashSet<>();
    //省略get和set方法
}

@Entity
@Table(name = "erp_priv")
public class Priv {
    @Id
    private Integer id;
    private String name;
    private String link;
    private Integer parentid;
    private String icon;
    //省略get和set方法
}

（2）测试类

public class RoleTest {
    private static EntityManagerFactory emf;
    private EntityManager em;
    private EntityTransaction tx;

    @BeforeClass
    public static void init() {
        emf = Persistence.createEntityManagerFactory("jpa");
    }

    @AfterClass
    public static void destory() {
        emf = null;
    }

    @Before
    public void setUp() {
        em = emf.createEntityManager();
        tx = em.getTransaction();
        tx.begin();
    }

    @After
    public void tearDown() {
        tx.commit();
        em.close();
    }

    @Test
    public void testAddRole() {
        Role role = new Role();
        role.setName("新增角色");
        role.setDescription("新增角色描述");

        role.getPrivs().add(em.getReference(Priv.class, 23));
        role.getPrivs().add(em.getReference(Priv.class, 24));

        em.persist(role);
    }

    @Test
    public void testDeleteRole() {
        Role role = em.find(Role.class, 5);
        em.remove(role);
    }

    @Test
    public void testGetRoles() {
        TypedQuery<Role> query = em.createQuery("from Role", Role.class);
        query.getResultList().forEach(role -> System.out.println(role.getPrivs()));
    }
}