使用JPA /休眠时,我遇到一个奇怪的问题。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;
}
}
这是我的主要伴侣课程:
@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;
}
}
合作伙伴有两个子类,即收货和交货。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;
}
}
这是交付类:
@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;
}
}
我正在得到这样的对象:
@Transactional
public Partner get(int id){
Partner partner = entityManager.find(Partner.class, id);
return partner;
}
如您所见,伙伴类包括一个对象列表和一个对象列表,它们分别存储在各自的表中,分别是收货和交货。
---在继续之前,我想指出数据库中显示了正确的条目数。仅在我的Java应用程序中获取对象时才会发生此问题。
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,则会再次显示一个对象和一个对象。当存在多个对象时,就会出现此问题。例如,如果添加了两个对象,但仅添加了一个对象,则将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。意外的结果用短划线包围。
<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外的结果?
您看到重复项的原因是因为您渴望获取子项,从而创建了外部联接。
(您可以使用@Fetch(FetchMode.SELECT),但这将导致其他查询来检索您的项目)
这是对您的问题的深入解答:Hibernate Criteria使用FetchType.EAGER多次返回子级。
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,如果您要通过条件从数据库中提取这些项目,则可以将结果转换器添加到查询结果中。
对于它的价值,hibernate建议在列表上使用集合
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