java使用Hibernate获取重复条目
我在使用JPA/Hibernate时遇到了一个奇怪的问题。我在测试中看到重复条目
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;
}
}
以下是我的主要合作伙伴课程:
@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;
}
}
Partner有两个子类,receive和Delivery。这是收据类:
@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;
}
}
以下是交付类:
@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;
}
}
我得到的对象如下:
@Transactional
public Partner get(int id){
Partner partner = entityManager.find(Partner.class, id);
return partner;
}
如您所见,partner类包括一个对象列表和一个对象列表,它们分别存储在各自的表receive和delivery中
---在进一步讨论之前,我想指出,数据库中显示的条目数量正确。此问题仅在获取Java应用程序中的对象时发生---
当我添加一个对象而不存在任何对象时,将显示一个对象而不显示任何对象,这是预期的。如果存在一个对象和一个对象,则会再次显示一个对象和一个对象,这是预期的。当存在多个或多个对象时,就会出现问题。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,请参见下面的测试用例表。意外结果被破折号包围
<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,为什么我会看到这些意想不到的结果
# 1 楼答案
您看到重复项的原因是您急切地获取子项,这将创建一个外部联接
(您可以使用@Fetch(FetchMode.SELECT),但这将导致额外的查询来检索您的项目)
Hibernate API reference indicating outer join takes place.
下面是对您的问题的深入回答:Hibernate Criteria returns children multiple times with FetchType.EAGER
您可以从列表切换到集合(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
hibernate建议使用集合而不是列表
# 2 楼答案
您可以将查询结果存储在
Set
中,它将为您删除重复项# 3 楼答案
如果您正在使用JPA:
否则,请参见Gernan的答案
# 4 楼答案
Hibernate不会为集合启用外部联接获取的查询返回不同的结果(即使我使用了distinct关键字)?阅读more,它可能会对你有所帮助
# 5 楼答案
也许您可以尝试使用DISTINCT属性进行查询
只需将此添加到您的标准中:
如果未使用标准:
如果它不能解决您的问题,请显示您的查询代码