将我的实体视为 CPU 和 PROCESSOR 与共享主键具有一对一的关系。一个 CPU 有一个处理器。
CPU.java
@Entity
@Table(name = "PKJoin_CPUt")
public class CPU {
private int id;
private String name;
private Processor processor;
@OneToOne(cascade = CascadeType.PERSIST, mappedBy = "cpu", optional = true,fetch=FetchType.LAZY)
public Processor getProcessor() {
return processor;
}
public void setProcessor(Processor processor) {
this.processor = processor;
if (null != processor) {
processor.setCpu(this);
}
}
private Processor2 processor2;
@OneToOne(cascade = CascadeType.PERSIST, mappedBy = "cpu", optional = true,fetch=FetchType.LAZY)
public Processor2 getProcessor2() {
return processor2;
}
public void setProcessor2(Processor2 processor2) {
this.processor2 = processor2;
if (null != processor2) {
processor2.setCpu(this);
}
}
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
if (null != processor) {
processor.setId(id);
}
if (null != processor2) {
processor2.setId(id);
}
}
public String getName() {
return name;
}
public void setName(String deptName) {
this.name = deptName;
}
}
处理器.java
@Entity
@Table(name = "PKJoin_Processor")
public class Processor {
private int id;
private String name;
private CPU cpu;
@OneToOne(fetch=FetchType.LAZY)
@PrimaryKeyJoinColumn
public CPU getCpu() {
return cpu;
}
public void setCpu(CPU cpu) {
this.cpu = cpu;
}
@Id
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
主.java
public class Main {
static EntityManagerFactory emf = Persistence.createEntityManagerFactory("Hello");
static EntityManager em = emf.createEntityManager();
public static void main(String[] a) throws Exception {
em.getTransaction().begin();
new Main().findData();
// new Main().persistData();
em.getTransaction().commit();
em.close();
emf.close();
}
public void findData(){
CPU cpu = em.find(CPU.class, 449);
System.out.println(cpu.getProcessor().getName());
}
}
这是这样执行的::
Hibernate: select cpu0_.id as id11_0_, cpu0_.name as name11_0_ from PKJoin_CPUt cpu0_ where cpu0_.id=?
Hibernate: select processor0_.id as id38_0_, processor0_.name as name38_0_ from PKJoin_Processor processor0_ where processor0_.id=?
Hibernate: select processor2x0_.id as id19_0_, processor2x0_.name as name19_0_ from PKJoin_Processor222 processor2x0_ where processor2x0_.id=?
乔
我不希望在仅获取 CPUName 属性时执行这三个查询。我也不想加入。每当我尝试获取 CPU 属性时,我只想执行第一个查询。需要解决方案吗?