条件 API 忽略 LAZY 提取

Question

我有两个实体 Customer 和 Product 具有惰性策略的一对多关系。

问题是获取不懒惰，产品集合总是获取所有相关产品。

public Optional<Customer> findById(final long customerId) {
    final EntityManager entityManager = sessionFactory.createEntityManager();
    final CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
    final CriteriaQuery<Customer> criteriaQuery = criteriaBuilder.createQuery(Customer.class);
    final Root<Customer> customerMetamodel = criteriaQuery.from(Customer.class);
    criteriaQuery.where(criteriaBuilder.equal(customerMetamodel.get("id"), customerId));
    final TypedQuery<Customer> query = entityManager.createQuery(criteriaQuery);
    return Optional.ofNullable(query.getSingleResult());
}

正如你所看到的，没有人提到 fetch eager，和实体类一样，都是懒惰的：

客户

@Data
@Builder
@EqualsAndHashCode
@NoArgsConstructor
@AllArgsConstructor
@Entity
@Table(name = "customer")
public class Customer {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String name;

    private int age;

    @OneToMany(mappedBy = "customer", fetch = FetchType.LAZY)
    private List<Product> products;

}

产品

@Entity
@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
@EqualsAndHashCode
@ToString(exclude = "customer")
@Table(name = "product")
public class Product {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private BigDecimal price;

    @ManyToOne(fetch = FetchType.LAZY)
    private Customer customer;

}

为什么 lazy work as eager 以及如何在这种情况下启用真正的懒惰模式？

UPDATE_1

H2 集成测试

@Test
public void testFindById() {
    Customer customer = customerRepository.create(Customer.builder().age(20).name("Denis").build());
    productRepository.create(Product.builder().customer(customer).price(new BigDecimal(100)).build());
    productRepository.create(Product.builder().customer(customer).price(new BigDecimal(200)).build());
    productRepository.create(Product.builder().customer(customer).price(new BigDecimal(300)).build());


    final Customer result = customerRepository.findById(customer.getId()).orElseThrow();

    assertEquals("Denis", result.getName());
    assertThrows(LazyInitializationException.class, () -> System.out.println(result.getProducts()));
}

我打电话给 .getProducts() 但预计 LazyInitializationException 因为会话已经关闭。

Answer 1

我猜你正在使用 Spring？尝试禁用 spring.jpa.properties.hibernate.enable_lazy_load_no_trans 无论如何这是一种反模式。

Answer 2

原因是 EntityManager 保持开放 session。并按需加载子实体。就我而言 .getProducts().

关闭session直接使用entityManager.close().

条件 API 忽略 LAZY 提取

Criteria API ignore LAZY fetch

java

hibernate

criteria

criteria-api

hibernate-criteria