我在使用 Spring 数据将下面提供的实体存储到数据库时遇到问题。这两者之间使用 OneToOne 关系。它仅在 parentObject 显式设置为 childObject 时有效。这不是一个很好的解决方案,因为我希望子对象根本没有父对象。有可能吗?非常相关的问题发布在这里
@Entity
@Table(name = "parent_object")
public class ParentObject {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id", unique = true, nullable = false)
private Long id;
@Column(name = "age")
private Long age;
@OneToOne(cascade = CascadeType.ALL, mappedBy = "parentObject")
private ChildObject childObject;
public ParentObject() {
}
public ParentObject(Long age, ChildObject childObject) {
this.age = age;
this.childObject = childObject;
}
public Long getId() {
return id;
}
public Long getAge() {
return age;
}
public ChildObject getChildObject() {
return childObject;
}
public void setChildObject(ChildObject childObject) {
this.childObject = childObject;
}
}
@Entity
@Table(name = "child_object")
public class ChildObject {
@Id
@Column(name = "child_id", unique = true, nullable = false)
private Long id;
@MapsId
@OneToOne
@JoinColumn(name = "child_id")
private ParentObject parentObject;
@Column(name = "name")
private String name;
public ChildObject() {
}
public ChildObject(String name) {
this.name = name;
}
public Long getId() {
return id;
}
public ParentObject getParentObject() {
return parentObject;
}
public String getName() {
return name;
}
public void setParentObject(ParentObject parentObject) {
this.parentObject = parentObject;
}
}
但是,我真的不喜欢将 parentObject 设置为 ChildObject:
ChildObject childObject = new ChildObject("name");
ParentObject parentObject = new ParentObject(12L, childObject);
childObject.setParentObject(parentObject);
这是共享ID的唯一方法吗?如果未明确设置 parentObject,则会引发以下错误:
Caused by: org.hibernate.id.IdentifierGenerationException: attempted to assign id from null one-to-one property [test.ChildObject.parentObject]
at org.hibernate.id.ForeignGenerator.generate(ForeignGenerator.java:83) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:101) ~[hibernate-core-5.0.11.Final.jar:5.0.11.Final]
at org.hibernate.jpa.event.internal.core.JpaPersistEventListener.saveWithGeneratedId(JpaPersistEventListener.java:67) ~[hibernate-entitymanager-5.0.11.Final.jar:5.0.11.Final]
您可以轻松地封装操作,以便不需要有问题的调用:实际上,您应该始终这样做,以便您的内存模型始终处于一致状态:
public class ParentObject{
public ParentObject(Long age, ChildObject childObject) {
this.age = age;
this.childObject = childObject;
childObject.setParentObject(this);
}
public void setChildObject(ChildObject childObject) {
this.childObject = childObject;
childObject.setParentObject(this);
}
}
现在,您的域模型 API 的客户端不需要知道任何关于从子到父的反向引用表单。
ChildObject childObject = new ChildObject("name");
ParentObject parentObject = new ParentObject(12L, childObject); //all relationships now set correctly
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