Hibernate：从@OneToMany 关系中获取重复项

Question

我是休眠新手，开始尝试一下。现在，当我尝试从 Apache Derby DB 获取“子类别”时，我遇到了重复问题。

我的结构：

Category
|__Sub category(s)
.....|__Product(s)

我的问题：

当我尝试获取“子类别”时，我得到了正确的，但它们是重复的。（见下文[儿童]）。我要的只是其中一个子类

children: Array(9)
0: {description: 'A place to collect your single malts.', id: 101, name: 'Single Malt', status: 'verified'}
1: {description: 'A place to collect your single malts.', id: 101, name: 'Single Malt', status: 'verified'}
2: {description: 'A place to collect your single malts.', id: 101, name: 'Single Malt', status: 'verified'}
3: {description: 'A place to collect your single malts.', id: 101, name: 'Single Malt', status: 'verified'}
4: {description: 'A place to collect your single malts.', id: 101, name: 'Single Malt', status: 'verified'}
5: {description: 'A place to collect your single malts.', id: 101, name: 'Single Malt', status: 'verified'}
6: {description: 'A place to collect your single malts.', id: 101, name: 'Single Malt', status: 'verified'}
7: {description: 'A place to collect your single malts.', id: 101, name: 'Single Malt', status: 'verified'}
8: {description: 'A place to collect your single malts.', id: 101, name: 'Single Malt', status: 'verified'}
length: 9
[[Prototype]]: Array(0)
description: "A place to collect your whiskies."
id: 100
name: "Whisky"
products: []
status: "verified"
[[Prototype]]: Object

我认为问题是：

我认为它与@OneToMany 注释和生成的连接有关table。因为我有 9 个“产品”属于同一个“子类别”。不幸的是，我不知道我的代码做错了什么会发生这种情况。

我想在从数据库中取出重复项后对其进行过滤。但感觉不对。如果有人能向我解释错误和最佳做法，我将不胜感激！

代码：

CategoryRepository.java

@RequestScoped
@Transactional(value = Transactional.TxType.REQUIRED,
        dontRollbackOn = {SqlException.class},
        rollbackOn = {SecurityException.class})
public class CategoryRepository implements CategoryCatalog {

    @Inject
    protected EntityManager em;

...

@Override
    public Category getCategory(Long id) {
        if (id == null) {
            return null;
        }
        try {
            Category category = this.em.find(Category.class, id);

            if(category != null){
                category.setProducts(this.filterFlaggedOrHiddenUserProducts(category.getProducts()));
            }
            return category;
        } catch (IllegalArgumentException ex){
            return null;
        }
    }

...

Category.java

@Entity(name = "CATEGORIES")
public class Category implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "CATEGORY_ID")
    private Long id;

    @ManyToOne
    private Category parentCategory;

    @OneToMany(mappedBy = "parentCategory", cascade = { CascadeType.PERSIST, CascadeType.MERGE}, fetch = FetchType.EAGER)
    private List<Category> children;

    @OneToMany(cascade = { CascadeType.PERSIST, CascadeType.MERGE}, fetch = FetchType.EAGER)
    private List<Product> products;

    @NotNull
    @Column(name = "CATEGORY_NAME")
    private String name;

...

数据库 tables 有数据

Table 个类别：

加入 table 个类别和产品：

Answer 1

解决方案

如果自己找到解决办法。我必须使用查询而不是查找。但我仍然不明白为什么会这样。如果有人能解释这种行为，我将不胜感激！

正在工作 - CategoryRepository.java

@RequestScoped
@Transactional(value = Transactional.TxType.REQUIRED,
        dontRollbackOn = {SqlException.class},
        rollbackOn = {SecurityException.class})
public class CategoryRepository implements CategoryCatalog {

    @Inject
    protected EntityManager em;

...

@Override
    public Category getCategory(Long id) {
        if (id == null) {
            return null;
        }
        try {
            Category category = this.em.createQuery("select c from CATEGORIES c WHERE CATEGORY_ID IS " + id, Category.class).getSingleResult();

            if(category != null){
                category.setProducts(this.filterFlaggedOrHiddenUserProducts(category.getProducts()));
            }
            return category;
        } catch (IllegalArgumentException ex){
            return null;
        }
    }

...

Hibernate：从@OneToMany 关系中获取重复项

Hibernate: Get duplicates as result out of @OneToMany relationship

hibernate

quarkus-panache