Question

我有一个名为category的表，它有父类别字段。我正在使用该字段来获取子类别。我已经检查了类似问题的答案，建议是（fetch = FetchType.EAGER）。但是我想把它加载为LAZY因为它是循环依赖。（再次指向同一张桌子）。

@Entity
@Table(name = "CATEGORY")
public class Category implements Serializable {
    @Id
    @Column(name = "ID")
    @GeneratedValue
    private Integer id;

    @Column(name = "CATEGORY_NAME", nullable = false, length = 40)
    private String name;

    @Column(name = "DESCRIPTION", nullable = false, length = 255)
    private String description;

    @Column(name = "DATE_CREATED", nullable = false)
    private Date dateCreated;

    @Column(name = "UUID", nullable = false, length = 40)
    private String uuid;

    @ManyToOne
    @JoinColumn(name = "PARENT_CATEGORY_ID")
    private Category parentCategory;

    @OneToMany(mappedBy = "parentCategory")
    private Collection<Category> subCategories = new LinkedHashSet<Category>();
}

错误是：

org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.hemanths.expense.manager.api.hibernate.entity.Category.subCategories, could not initialize proxy - no Session
    at org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:566)
    at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:186)
    at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:545)
    at org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:124)
    at org.hibernate.collection.internal.PersistentBag.iterator(PersistentBag.java:266)

有人可以帮我找到解决方案吗？

Answer 1

如果要获取注释为延迟加载的对象集合，并且您不希望将加载机制转换为eager，则必须在同一session中获取集合或transaction您只需为集合调用size()方法即可获取父对象，例如，如果您有这样的服务方法：

public Category getCategortById(int id) {
  Category category = categoryDao.getCategortById(id);
  category.getSubCategories().size();  // Hibernate will fetch the collection once you call the size()
}

此外，如果你想要一个更干净的方法，你可以使用Hibernate.initalize()方法来初始化任何延迟加载对象或集合，所以它可能是这样的

 public Category getCategortById(int id) {
  Category category = categoryDao.getCategortById(id);
  Hibernate.initialize(category.getSubCategories());
}

您可以查看有关初始化合并here

的更多信息

Answer 2

查看堆栈跟踪，看起来这是一个会话管理问题。尝试查看您打开会话的位置以及您正在使用的SessionContext？

org.hibernate.LazyInitializationException：懒得初始化角色集合

2 个答案: