Question

我正在学习JPA文档，遇到以下几行：

锁定实体包含外部实体的实体关系 key也将被锁定，但不会被引用的实体的状态（除非明确锁定这些实体）。元素集合和实体不包含外键的关系（例如映射到连接表的关系或目标实体的单向一对多关系包含外键）默认情况下不会被锁定。

来自here（PessimisticLockScope.NORMAL）

我想知道如何解释这些线条。如果PessimisticLockScope设置为EXTENDED，则连接表中的行也会被锁定（但不是相关实体本身），因此在使用NORMAL值时会锁定什么？确保实体行（如果继承策略为JOINED或TABLE_PER_CLASS或者SecondaryTable，则为行），但“实体关系”是什么意思：

锁定实体包含外部实体的实体关系密钥也将被锁定

在PessimisticLockScope.NORMAL？

的上下文中

Answer 1

实体关系映射到数据库FK关联。

PessimisticLockScope.NORMAL将发出一个非常激进的数据库独占锁定：

实体分离的表行
在连接表继承结构中，基表和子类表都将被锁定
具有实际FK关系的所有@ManyToOne和@OneToOne关联表格行（例如，@JoinColumn的一侧）。但这意味着您无法更改FK信息，这意味着您无法将其设置为null或任何其他不同的值。因此，只有FK列值被锁定而不是其他表关联的FK行。

@OneToMany，@ManyToMany和非拥有@OneToOne和@ManyToOne关联不会被锁定，因为这些关联只有面向对象的等价物并且锁定仅在数据库级别发生。有关详细信息，请查看this article。

PessimisticLockScope.EXTENDED也将扩展为@OneToMany和@ManyToMany关联。但同样，这仅适用于FK列值而不适用于整行。因此，此锁定将阻止向/ @OneToMany / @ManyToMany关联添加/删除元素。它不会阻止包含的元素更新。为此，您必须锁定每个包含的实体。

Answer 2

以下是关于这个问题的一些实验。我使用Hibernate 4.3.6作为JPA提供程序，使用MySQL 5.6作为数据库。

很少有测试实体 - TestPerson，TestUser，TestOrder

TestUser扩展了TestPerson（带有JOINED继承），TestUser有一个双向的OneToMany TestOrders列表

@Entity
@Inheritance(strategy = InheritanceType.JOINED)
public class TestPerson {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)   
    private long id;

    private String name;
    private String address;

    //getters and setters



@Entity
public class TestUser extends TestPerson {

    @OneToMany(fetch=FetchType.LAZY,mappedBy="user")   
    private List<TestOrder> orders ;

    //getters and setters


@Entity
public class TestOrder {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)   
    private long id;

    @ManyToOne
    @JoinTable(name="test_user_orders")
    private TestUser user;

    private String orderNumber ;

    //getters and setters**

数据创建代码：

         em.getTransaction().begin();            
         TestUser user = new TestUser();
         user.setName("TestUser"+System.currentTimeMillis());
         user.setAddress("TestUserAddress1");
         em.persist(user);
         List<TestOrder> orders = new ArrayList();
         for (int i=1;i<6;i++){
         TestOrder order = new TestOrder();
         order.setOrderNumber("ON"+System.currentTimeMillis());
         order.setUser(user);
         em.persist(order);
         orders.add(order);
         }
         user.setOrders(orders);

         em.getTransaction().commit();
         em.close();




mysql> select * from test_person;
+----+------------------+-----------------------+
| id | address          | name                  |
+----+------------------+-----------------------+
|  1 | TestUserAddress1 | TestUser1406031063539 |
+----+------------------+-----------------------+
1 row in set (0.00 sec)


mysql> select * from test_user;
+----+
| id |
+----+
|  1 |
+----+


mysql> select * from test_order;
+----+-----------------+
| id | order_number    |
+----+-----------------+
|  1 | ON1406031063627 |
|  2 | ON1406031063673 |
|  3 | ON1406031063678 |
|  4 | ON1406031063683 |
|  5 | ON1406031063686 |
+----+-----------------+



mysql> select * from test_user_orders;
+------+----+
| user | id |
+------+----+
|    1 |  1 |
|    1 |  2 |
|    1 |  3 |
|    1 |  4 |
|    1 |  5 |
+------+----+

现在正在查找MnayToOne方，即TestOrder

Map<String, Object> map = new HashMap<String, Object>();
 map.put("javax.persistence.lock.scope", PessimisticLockScope.EXTENDED);
 TestOrder order  = em2.find(TestOrder.class, new Long(1), LockModeType.PESSIMISTIC_WRITE, map);

注意＆＃34;更新＆＃34;在查询悲观锁定。此查询也包含连接表。

 select
        testorder0_.id as id1_8_0_,
        testorder0_.order_number as order_nu2_8_0_,
        testorder0_1_.user as user1_11_0_ 
    from
        test_order testorder0_ 
    left outer join
        test_user_orders testorder0_1_ 
            on testorder0_.id=testorder0_1_.id 
    where
        testorder0_.id=? for update

Hibernate: 
    select
        testuser0_.id as id1_9_0_,
        testuser0_1_.address as address2_9_0_,
        testuser0_1_.name as name3_9_0_ 
    from
        test_user testuser0_ 
    inner join
        test_person testuser0_1_ 
            on testuser0_.id=testuser0_1_.id 
    where
        testuser0_.id=?

此外，当我查询用户时，此次仅用户层次结构中涉及的表被＆＃34;锁定以用于更新＆＃34;

 Map<String, Object> map = new HashMap<String, Object>();
        map.put("javax.persistence.lock.scope", PessimisticLockScope.EXTENDED);
        TestUser user  = em2.find(TestUser.class, new Long(2), LockModeType.PESSIMISTIC_WRITE,map);
        user.getOrders().size(); // to force initialization of orders

生成的SQL是：

        select
        testuser0_.id as id1_9_0_,
        testuser0_1_.address as address2_9_0_,
        testuser0_1_.name as name3_9_0_ 
    from
        test_user testuser0_ 
    inner join
        test_person testuser0_1_ 
            on testuser0_.id=testuser0_1_.id 
    where
        testuser0_.id=? for update

Hibernate: 
    select
        orders0_.user as user1_9_0_,
        orders0_.id as id2_11_0_,
        testorder1_.id as id1_8_1_,
        testorder1_.order_number as order_nu2_8_1_,
        testorder1_1_.user as user1_11_1_ 
    from
        test_user_orders orders0_ 
    inner join
        test_order testorder1_ 
            on orders0_.id=testorder1_.id 
    left outer join
        test_user_orders testorder1_1_ 
            on testorder1_.id=testorder1_1_.id 
    where
        orders0_.user=?

JPA PessimisticLockScope.NORMAL并锁定“关系”

2 个答案: