惠州什么是JPA单向一对一映射？_北大青鸟IT学校

Java是现在非常主流的编程语言之一，很多人想转行学习IT，首选Java语言。那么什么是JPA单向一对一映射？下面就让我们一起来看看惠州北大青鸟老师是怎么回答的。

以下代码显示了如何进行单向一对一映射。

实例

下面的代码来自PersonDaoImpl.java。

package cn.w3cschool.common;

import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;

import org.springframework.transaction.annotation.Transactional;

@Transactionalpublic class PersonDaoImpl {  public void test() {

   Professor emp = new Professor();
   emp.setName("name");
   emp.setSalary(12345);
   

   ParkingSpace ps = new ParkingSpace();
   ps.setLot(1);
   ps.setLocation("East");
   emp.setParkingSpace(ps);
   
   em.persist(ps);
   em.persist(emp);
 }

 @PersistenceContext  private EntityManager em;
}

以下代码来自Professor.java。

package cn.w3cschool.common;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToOne;

@Entitypublic class Professor {
 @Id @GeneratedValue(strategy=GenerationType.IDENTITY)  private int id;  private String name;  private long salary;
 
 @OneToOne
 @JoinColumn(name="PSPACE_ID")
 private ParkingSpace parkingSpace;  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;
 }  public long getSalary() {
     return salary;
 }  public void setSalary(long salary) {
     this.salary = salary;
 }  
 public ParkingSpace getParkingSpace() {
     return parkingSpace;
 }  
 public void setParkingSpace(ParkingSpace parkingSpace) {
     this.parkingSpace = parkingSpace;
 }  public String toString() {
     return "Employee id: " + getId() + " name: " + getName() +
            " with " + getParkingSpace();
 }
}

下面的代码来自ParkingSpace.java。

package cn.w3cschool.common;


import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name="PARKING_SPACE")public class ParkingSpace {
   @Id @GeneratedValue(strategy=GenerationType.IDENTITY)    private int id;    private int lot;    private String location;    public int getId() {
       return id;
   }    
   public void setId(int id) {
       this.id = id;
   }    public int getLot() {
       return lot;
   }    public void setLot(int lot) {
       this.lot = lot;
   }    
   public String getLocation() {
       return location;
   }    
   public void setLocation(String deptName) {
       this.location = deptName;
   }    public String toString() {
       return "ParkingSpace id: " + getId() + " lot: " + getLot() +               ", location: " + getLocation();
   }

}

以下是数据库转储。

Table Name: PARKING_SPACE
Row:
   Column Name: ID,
   Column Type: INTEGER:
   Column Value: 1

   Column Name: LOCATION,
   Column Type: VARCHAR:
   Column Value: East

   Column Name: LOT,
   Column Type: INTEGER:
   Column Value: 1

Table Name: PROFESSOR
Row:
   Column Name: ID,
   Column Type: INTEGER:
   Column Value: 1

   Column Name: NAME,
   Column Type: VARCHAR:
   Column Value: name

   Column Name: SALARY,
   Column Type: BIGINT:
   Column Value: 12345

   Column Name: PSPACE_ID,
   Column Type: INTEGER:
   Column Value: 1

想学Java的同学们，可以来惠州北大青鸟新方舟校区详细了解。

Java

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