Hibernate 子对象中存在重复数据

我将SpringBoot2.1与SpringDataJPA和hibernate一起使用

@Entity
public class Factories{
    @Id
    @SequenceGenerator(name = "factories_id_seq", sequenceName = "factories_id_seq", allocationSize = 1)
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "factories_id_seq")
    private Integer id;

    @OneToMany(mappedBy = "factory", cascade = CascadeType.ALL, orphanRemoval = true, fetch = FetchType.LAZY)
    private List<Machines> machines = new ArrayList<>();

    @ElementCollection(fetch = FetchType.LAZY)
    private Set<String> emails = new HashSet<>();

}   

我试着用清晰的和不清晰的

我的工厂id为1

有3台机器和3封电子邮件

我得到的不是3台机器和3封电子邮件，而是9台机器。数据库中只有3个

就像笛卡尔积完成了一样

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任何想法

您只需在Hibernate或任何JPA中遇到

MultipleBagFetch

问题。是的，你是对的，你所看到的是笛卡尔积的结果，但这一切照旧。有更多的帖子在讨论同样的问题。要解决您的问题，您有3个选项：

a） 将提取拆分为两个连接查询 b） 使用特定于Hibernate的解决方案： 或

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@Fetch是hibernate，热JPA标准：

SELECT distinct f from Factories f "
        + "LEFT JOIN FETCH f.machines "
        + "Left JOIN FETCH f.emails "
        + "Left JOIN FETCH f.cities "
        + "where f.id=:id

SELECT distinct f from Factories f "
        + "LEFT JOIN FETCH f.machines "
        + "Left JOIN FETCH f.cities "
        + "where f.id=:id

SELECT distinct f from Factories f "
        + "LEFT JOIN FETCH f.machines "
        + "Left JOIN FETCH f.emails "
        + "where f.id=:id

@LazyCollection(LazyCollectionOption.FALSE)

@Fetch(value = FetchMode.SUBSELECT)