Hibernate 5.4运行时字节码增强器enableLazyInitialization无法工作

Question

我以base教程项目(链接) >本机引导>注释示例为例。

Hibernate版本: 5.4.29

实体：

@Entity
public class Customer {
    
    @Id
    @GeneratedValue
    private Integer id;

    private String name;

    @Basic( fetch = FetchType.LAZY )
    private UUID accountsPayableXrefId;

    @Lob
    @Basic( fetch = FetchType.LAZY )
    @LazyGroup( "lobs" )
    private Blob image;

    // getters and setters

}

在hibernate.cfg.xml中，我添加了以下行

<property name="hibernate.enhancer.enableLazyInitialization">true</property>

单元测试

public void testLazy() throws SerialException, SQLException {
    
    Session session = sessionFactory.openSession();
    session.beginTransaction();
    
    byte[] bytes = "A byte array".getBytes();
    Blob blob = new javax.sql.rowset.serial.SerialBlob(bytes);
    Customer customer = new Customer();
    customer.setName("John Doe");
    customer.setAccountsPayableXrefId(UUID.randomUUID());
    customer.setImage(blob);
    
    session.save( customer );
    
    Integer id = customer.getId();
    
    session.getTransaction().commit();
    session.close();

    session = sessionFactory.openSession();
    session.beginTransaction();
    
    Customer found = session.find(Customer.class, id);
    System.out.println("Customer: " + found.getAccountsPayableXrefId());
    System.out.println("Customer: " + found.getImage().length());

    session.getTransaction().commit();
    session.close();
}

我希望在实体提取字段中标记为lazy的字段甚至不会从DB中被选中，直到显式引用它们，但我在日志中看到：

Hibernate: select customer0_.id as id1_0_0_, customer0_.accountsPayableXrefId as accounts2_0_0_, customer0_.image as image3_0_0_, customer0_.name as name4_0_0_ from Customer customer0_ where customer0_.id=?

查询提供了相同的结果(懒惰= false)

List<Customer> result = session.createQuery( "from Customer" ).list();
for ( Customer c : result ) {
    System.out.println("Customer: " + c.getAccountsPayableXrefId());
    System.out.println("Customer: " + c.getImage().length());
}

在跟踪日志中有这样的行

[2021-03-17 20:44:10.349][][DBG][org.hibernate.cfg.Ejb3Column][main] Binding column: Ejb3Column{table=org.hibernate.mapping.Table(Customer), mappingColumn=accountsPayableXrefId, insertable=true, updatable=true, unique=false} 
[2021-03-17 20:44:10.349][][DBG][org.hibernate.cfg.annotations.PropertyBinder][main] MetadataSourceProcessor **property accountsPayableXrefId with lazy=true** 
...
[2021-03-17 20:44:10.351][][DBG][org.hibernate.cfg.annotations.PropertyBinder][main] MetadataSourceProcessor property image with lazy=true 
...
[2021-03-17 20:44:10.461][][DBG][org.hibernate.internal.SessionFactoryImpl][main] Instantiating session factory with properties: {... hibernate.enhancer.enableLazyInitialization=true} 
...
[... 20:44:11.382][][TRC][o.h.event.internal.DefaultLoadEventListener][main] Loading entity: [o.h.tutorial.annotations.Customer#1] 
[... 20:44:11.384][][TRC][o.h.persister.entity.AbstractEntityPersister][main] Fetching entity: [o.h.tutorial.annotations.Customer#1] 
[... 20:44:11.386][][DBG][o.h.SQL][main] select customer0_.id as id1_0_0_, customer0_.accountsPayableXrefId as accounts2_0_0_, customer0_.image as image3_0_0_, customer0_.name as name4_0_0_ from Customer customer0_ where customer0_.id=? 
[... 20:44:11.387][][TRC][o.h.type.descriptor.sql.BasicBinder][main] binding parameter [1] as [INTEGER] - [1] 
[... 20:44:11.457][][TRC][o.h.loader.plan.exec.process.internal.EntityReferenceInitializerImpl][main] hydrating entity state 
[... 20:44:11.459][][TRC][o.h.persister.entity.AbstractEntityPersister][main] Hydrating entity: [o.h.tutorial.annotations.Customer#1] 
[... 20:44:11.460][][TRC][o.h.type.descriptor.sql.BasicExtractor][main] extracted value ([accounts2_0_0_] : [BINARY]) - [a897b3c2-c19c-4f36-b0a1-17bca893f433] 
[... 20:44:11.464][][TRC][o.h.type.descriptor.sql.BasicExtractor][main] extracted value ([image3_0_0_] : [BLOB]) - [{blob}] 
[... 20:44:11.465][][TRC][o.h.type.descriptor.sql.BasicExtractor][main] extracted value ([name4_0_0_] : [VARCHAR]) - [John Doe] 
[... 20:44:11.466][][TRC][o.h.loader.plan.exec.process.internal.AbstractRowReader][main] Total objects hydrated: 1 
[... 20:44:11.467][][DBG][o.h.engine.internal.TwoPhaseLoad][main] Resolving attributes for [o.h.tutorial.annotations.Customer#1] 
[... 20:44:11.468][][DBG][o.h.engine.internal.TwoPhaseLoad][main] Processing attribute `accountsPayableXrefId` : value = a897b3c2-c19c-4f36-b0a1-17bca893f433 
[... 20:44:11.468][][DBG][o.h.engine.internal.TwoPhaseLoad][main] Attribute (`accountsPayableXrefId`)  - enhanced for lazy-loading? - false 
[... 20:44:11.468][][DBG][o.h.engine.internal.TwoPhaseLoad][main] Processing attribute `image` : value = blob0: X'412062797465206172726179' 
[... 20:44:11.468][][DBG][o.h.engine.internal.TwoPhaseLoad][main] Attribute (`image`)  - enhanced for lazy-loading? - false 
[... 20:44:11.468][][DBG][o.h.engine.internal.TwoPhaseLoad][main] Processing attribute `name` : value = John Doe 
[... 20:44:11.468][][DBG][o.h.engine.internal.TwoPhaseLoad][main] Attribute (`name`)  - enhanced for lazy-loading? - false 
[... 20:44:11.468][][DBG][o.h.engine.internal.TwoPhaseLoad][main] Done materializing entity [o.h.tutorial.annotations.Customer#1] 

所以看起来懒散加载对我的例子不起作用。我做错什么了？

Answer 1

尝试使用“域模型的构建时增强”而不是运行时。设置更简单，效率更高，因为在编译过程中更改了实体的字节码：

<build>
  <plugins>
    [...]
    <plugin>
      <groupId>org.hibernate.orm.tooling</groupId>
      <artifactId>hibernate-enhance-maven-plugin</artifactId>
      <version>${hibernate.version}</version>
      <executions>
        <execution>
          <configuration>
            <failOnError>true</failOnError>
            <enableLazyInitialization>true</enableLazyInitialization>
          </configuration>
          <goals>
            <goal>enhance</goal>
          </goals>
        </execution>
      </executions>
    </plugin>
    [...]
  </plugins>
</build>

之后，在实体类中，您可以使用@Basic( fetch = FetchType.LAZY )注释来加载延迟列：

@Entity
public class Customer {
    
    @Id
    @GeneratedValue
    private Integer id;

    private String name;

    @Basic( fetch = FetchType.LAZY )
    private UUID accountsPayableXrefId;

    @Basic( fetch = FetchType.LAZY )
    private Blob image;

    // getters and setters
}

若要验证，请将SQL添加到application.yaml文件中：

spring:
  jpa:
    properties:
      hibernate.show_sql: true
      hibernate.format_sql: true
logging:
  level:
    org.hibernate.type.descriptor.sql.BasicBinder: TRACE

并使用maven构建应用程序，因为如果尝试从IntelliJ或Eclipse中运行该插件，则不会调用该插件：

./mvnw clean spring-boot:run