使用Hibernate获取重复的条目

Question

我在使用JPA/Hibernate时遇到了一个奇怪的问题.我在测试期间看到重复的条目.

这是我的BaseEntity类:

@Entity
@Inheritance(strategy=InheritanceType.TABLE_PER_CLASS)
public abstract class BaseEntity {

    @Id
    @Column(name = "ID", updatable = false, nullable = false)
    @GenericGenerator(name = "uniqueIDGenerator", strategy = "org.hibernate.id.enhanced.SequenceStyleGenerator", parameters = {
            @org.hibernate.annotations.Parameter(name = "sequence_name", value = "ID_SEQUENCE"),
            @org.hibernate.annotations.Parameter(name = "increment_size", value = "100"),
            @org.hibernate.annotations.Parameter(name = "optimizer ", value = "pooled") })
    @GeneratedValue(generator = "uniqueIDGenerator")
    @NotNull
    protected int id;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

}

这是我的主要合作伙伴类:

@Entity
@Table(name = "partner")
public class Partner extends BaseEntity{

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

    @OneToMany(mappedBy="partner", fetch=FetchType.EAGER)
    @Cascade(CascadeType.DELETE)
    private List<Receipt> receipts;

    @OneToMany(mappedBy="partner", fetch=FetchType.EAGER)
    @Cascade(CascadeType.DELETE)
    private List<Delivery> deliveries;

    public Partner() {
        setReceipts(new ArrayList<Receipt>());
        setDeliveries(new ArrayList<Delivery>());
    }

    public Partner(String name){
        this();

        this.setName(name);
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public List<Receipt> getReceipts() {
        return receipts;
    }

    public void setReceipts(List<Receipt> receipts) {
        this.receipts = receipts;
    }

    public List<Delivery> getDeliveries() {
        return deliveries;
    }

    public void setDeliveries(List<Delivery> deliveries) {
        this.deliveries = deliveries;
    }
}

合作伙伴有两个子类,Receipt和Delivery.这是Receipt类:

@Entity
@Table(name = "receipt")
public class Receipt extends BaseEntity{

    @ManyToOne(fetch=FetchType.LAZY)
    @JoinColumn(name="partnerId")
    private Partner partner;

    @Column(name = "name")
    private String name;
    @Column(name = "json")
    private String json;

    @Transient
    private ReceiptContainer receiptContainer;


    public Receipt() {
    }
    public Receipt(String name){
        this();

        this.setName(name);
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getJson() {
        return json;
    }

    public void setJson(String json) {
        this.json = json;
    }

    public ReceiptContainer getReceiptContainer() {
        return receiptContainer;
    }

    public void setReceiptContainer(ReceiptContainer receiptContainer) {
        this.receiptContainer = receiptContainer;
    }

    public Partner getPartner() {
        return partner;
    }

    public void setPartner(Partner partner) {
        this.partner = partner;
    }

}

这是Delivery类:

@Entity
@Table(name = "delivery")
public class Delivery extends BaseEntity{

    @ManyToOne(fetch=FetchType.LAZY)
    @JoinColumn(name="partnerId")
    private Partner partner;

    @Column(name = "name")
    private String name;
    @Column(name = "json")
    private String json;

    @Transient
    private DeliveryContainer deliveryContainer;


    public Delivery() {
    }
    public Delivery(String name){
        this();

        this.setName(name);
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getJson() {
        return json;
    }

    public void setJson(String json) {
        this.json = json;
    }

    public DeliveryContainer getDeliveryContainer() {
        return deliveryContainer;
    }

    public void setDeliveryContainer(DeliveryContainer deliveryContainer) {
        this.deliveryContainer = deliveryContainer;
    }

    public Partner getPartner() {
        return partner;
    }

    public void setPartner(Partner partner) {
        this.partner = partner;
    }

}

我得到这样的对象:

@Transactional
public Partner get(int id){
    Partner partner = entityManager.find(Partner.class, id);
    return partner;
}

如您所见,合作伙伴类包括一个对象列表和一个对象列表,它们分别存储在自己的表,收据和交付中.

---在进一步讨论之前,我想指出数据库中显示的条目数正确.只有在我的Java应用程序中获取对象时才会出现此问题.---

当我添加一个对象并且不存在任何对象时,将显示一个对象,并且不显示任何对象,这是预期的.如果存在一个对象和一个对象,则再次显示一个对象和一个对象,这是预期的.当存在多个或对象时,会发生此问题.例如,如果添加了两个对象但只添加了一个对象,则会显示两个对象和两个对象.

为了更好地说明这一点,请参阅下面的测试用例表.用破折号包围意外的结果.

<Receipt> Obj Added | <Delivery> Obj Added | <Receipt> Obj Displayed | <Delivery> Obj Displayed
         0          |          0           |           0             |            0
         0          |          1           |           0             |            1
         1          |          0           |           1             |            0
         1          |          1           |           1             |            1
         1          |          2           |        ---2---          |         ---2---
         2          |          1           |        ---2---          |         ---2---
         2          |          2           |        ---4---          |         ---4---

我的问题是,为什么我看到这些意想不到的结果？

Answer 1

你看到重复的原因是因为你正在急切地抓取孩子,这正在创建一个外部联接.

(您可以使用@Fetch(FetchMode.SELECT),但这会导致其他查询以检索您的项目)

指示外连接的Hibernate API引用发生.

以下是对您的问题的深入解答:Hibernate Criteria使用FetchType.EAGER多次返回子项

您可以从List切换到Set(如果这样做,请确保覆盖equals/compareTo/hashCode).或者,如果要通过条件从数据库中提取这些项,则可以将结果转换器添加到查询结果中.

值得一提的是,hibernate建议在列表上使用集合

Answer 2

也许您可以尝试使用DISTINCT属性进行查询.

只需将其添加到您的标准:

criteria.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY);

如果您没有使用标准:

SELECT DISTINCT <QUERY>

如果它无法解决您的问题,请显示您的查询代码.