將@Transactional添加到測試中，以避免org.hibernate.LazyInitializationException no Session錯誤。 為什么需要它？

Question

我用@Transactional注釋了一種測試方法，以避免：

org.hibernate.LazyInitializationException: could not initialize proxy [com....OrderEntity#6def569a-ebf2-473e-b1b1-8b67e62fd17d] - no Session

    at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:169)
    at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:309)
    at org.hibernate.proxy.pojo.bytebuddy.ByteBuddyInterceptor.intercept(ByteBuddyInterceptor.java:45)
    at org.hibernate.proxy.ProxyConfiguration$InterceptorDispatcher.intercept(ProxyConfiguration.java:95)
    at com...orders.OrderEntity$HibernateProxy$wwLGAOuY.getDescription(Unknown Source)

我不知道為什么需要它，並且想知道我的應用程序配置是否正確。

import lombok.Getter;
import lombok.Setter;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;
import java.util.Date;
import java.util.UUID;

@Entity
@Table(name = "orders")
@Getter
@Setter
public class OrderEntity {

    @Id
    @GeneratedValue
    private UUID uid;
    private Date created;
    private Date updated;
    private String description;

}

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

import java.util.List;
import java.util.UUID;

@Repository
public interface OrderRepository extends JpaRepository<OrderEntity, UUID> {

    List<OrderEntity> findByDescription(String description);
}

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

import java.util.List;
import java.util.UUID;

@Service
@Transactional
public class OrderService
{

    private OrderRepository repository;

    @Autowired
    public OrderService(OrderRepository repository) {
        this.repository = repository;
    }

    public List<OrderEntity> findAll() {
        return repository.findAll();
    }

    public OrderEntity save(OrderEntity order) {
        return repository.save(order);
    }

    public OrderEntity getOne(UUID uid) {
        return repository.getOne(uid);
    }
}

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.transaction.annotation.Transactional;

import static org.junit.Assert.assertEquals;

@RunWith(SpringRunner.class)
@SpringBootTest
public class OrderServiceTest {

    @Autowired
    private OrderService service;

    @Test
    @Transactional
    public void testSave() {

        OrderEntity order = new OrderEntity();
        order.setDescription("Order description");

        OrderEntity saved = service.save(order);
        System.out.println(saved.getDescription());

        OrderEntity persisted = service.getOne(saved.getUid());
        // throws LazyInitializationException without @Transactional
        System.out.println(persisted.getDescription()); 

        assertEquals(persisted.getDescription(), order.getDescription());
    }
}

我什至添加了@EnableTransactionManagement但沒有區別：

import org.springframework.context.annotation.Configuration;
import org.springframework.transaction.annotation.EnableTransactionManagement;

@Configuration
@EnableTransactionManagement
public class PersistenceJPAConfig {
}

Answer 1

getOne和findOne之間的區別在於，即使數據庫中沒有實際的行，第一個也總是返回惰性代理。 惰性代理需要打開的EntityManager才能進行操作。 但是，由於您的測試方法不在單個事務中運行，因此getOne方法結束后， EntityManager將立即關閉。

如果沒有打開EntityManager ，則對該對象的調用將失敗，因為它無法再從數據庫中檢索值。

要解決此問題，請使用findOne而不是getOne或者使您的測試方法具有事務性。 但是后者會對您的測試用例產生其他影響（它將從findOne調用返回相同的對象，因為它還將重用單個EntityManager ）。