JPA视频学习（一）增删改查

1.依赖jar包：

2.配置文件：

<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/persistence
    http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd" version="1.0">
    
	<persistence-unit name="HelloJPAPU" transaction-type="RESOURCE_LOCAL">
		<provider>org.hibernate.ejb.HibernatePersistence</provider>
  		<properties>
  		    <property name="hibernate.dialect" value="org.hibernate.dialect.MySQL5Dialect"/>
			<property name = "hibernate.connection.driver_class" value = "com.mysql.jdbc.Driver"/>
			<property name = "hibernate.connection.url" value = "jdbc:mysql://localhost:3306/jpa?useUnicode=true&amp;characterEncoding=UTF-8"/>
			<property name = "hibernate.connection.username" value = "root"/>
			<property name="hibernate.max_fetch_depth" value="3"/>
            <property name="hibernate.hbm2ddl.auto" value="update"/>  
	  	</properties>
	</persistence-unit>
  
</persistence>

3.定义实体bean：

import java.util.Date;
import javax.persistence.Basic;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.EnumType;
import javax.persistence.Enumerated;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Lob;
import javax.persistence.Table;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;
import javax.persistence.Transient;

@Entity
public class Person {

	private Integer id;
	private String name;
	private Date birthday;//1988-02-01
	private Gender gender=Gender.MAN;
	private String info;
	private Byte[] file;
	private String imagePathString;
	
	public Person(){
		
	}
	
	public Person(String name){
		this.name=name;
	}
	@Id @GeneratedValue(strategy=GenerationType.AUTO)
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	
	@Column(length=10,nullable=false)
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}

	@Temporal(TemporalType.DATE)
	public Date getBirthday() {
		return birthday;
	}

	public void setBirthday(Date birthday) {
		this.birthday = birthday;
	}

	@Enumerated(EnumType.STRING)//将索引值保存进数据库
	@Column(length=5,nullable=false) //设置长度
	public Gender getGender() {
		return gender;
	}

	public void setGender(Gender gender) {
		this.gender = gender;
	}

	@Lob //大数据字段的说明，用在String上面是个大文本类型
	public String getInfo() {
		return info;
	}

	public void setInfo(String info) {
		this.info = info;
	}

	@Lob //大数据字段说明，用在这里是存放二进制数据的类型
	@Basic(fetch=FetchType.LAZY)//延迟加载，当访问此属性的get方法时才会从数据库加载到内存，
	                            //此时必须保证em处于打开状态，否则会有延迟加载错误。
	public Byte[] getFile() {
		return file;
	}

	public void setFile(Byte[] file) {
		this.file = file;
	}

	public void setImagePathString(String imagePathString) {
		this.imagePathString = imagePathString;
	}

	@Transient //此属性不成为持久化字段
	public String getImagePathString() {
		return imagePathString;
	}
	
	
	
	
}

枚举类：

package com.persia.jpa;

public enum Gender {
  MAN,WOMAN
}

4.添加测试方法：

package junit.test;
import java.util.Date;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import org.junit.BeforeClass;
import org.junit.Test;
import com.persia.jpa.Person;

public class PersonTest {

	@BeforeClass
	public static void setUpBeforeClass() throws Exception {
	
	}
    
	//@Test 
	public void save(){
		EntityManagerFactory fac=Persistence.createEntityManagerFactory("HelloJPAPU");
		//此时数据库表已经建立，若没有表，很可能是实体的注解出错了。
		EntityManager em=fac.createEntityManager();
		em.getTransaction().begin();//开启事务
		Person person=new Person("linda");
		person.setBirthday(new Date());
		em.persist(person);
		em.getTransaction().commit();//提交事务
		em.close();
		fac.close();
	}
	
	//@Test 
	public void getPerson(){
		//读取不用开启事务
		EntityManagerFactory fac=Persistence.createEntityManagerFactory("HelloJPAPU");
		EntityManager em=fac.createEntityManager();
		
		Person p=em.find(Person.class, 1);//不存在返回null
		System.out.println(p.getName());
		
		em.close();
		fac.close();
	}
	
	//@Test 
	public void getPerson2(){
		//读取不用开启事务
		EntityManagerFactory fac=Persistence.createEntityManagerFactory("HelloJPAPU");
		EntityManager em=fac.createEntityManager();
		
		Person p=em.getReference(Person.class, 2);//延迟初始化,不会立刻从数据库得到记录，只是得到一个代理对象	                                         
		System.out.println(p.getName()); //当我们访问这个代理对象的属性时，才从数据库得到记录,此时必须保证em是开着的，否则出现延迟加载例外。
		                                //此时若访问时，不存在该实体则抛出例外EntityNotFoundException
		em.close();
		fac.close();
	}
	
	//@Test
	public void updatePerson(){
		EntityManagerFactory fac=Persistence.createEntityManagerFactory("HelloJPAPU");
		EntityManager em=fac.createEntityManager();
		em.getTransaction().begin();//开启事务
		Person p=em.find(Person.class, 1);
		p.setName("helloworld");//此时可以更新，主要有如下：
		/**
		 * 1.跟当前事务关联
		 * 2.实体bean的状态为托管状态
		 * 
		 * 实体的状态：
		 * 1.新建 new 
		 * 2.托管 managed
		 * 3.游离（脱管）
		 * 4.删除
		 */
		em.getTransaction().commit();//提交事务
		em.close();
		fac.close();
	}
	
	//@Test
	public void updatePerson2(){
		EntityManagerFactory fac=Persistence.createEntityManagerFactory("HelloJPAPU");
		EntityManager em=fac.createEntityManager();
		em.getTransaction().begin();//开启事务
		Person p=em.find(Person.class, 1);
		em.clear();//把实体管理器中的所有实体变成游离状态,此时应该用merge来更新
		p.setName("hello3");//此时可以更新，主要有如下：
		em.merge(p);//用于把对处于游离状态的实体bean的更新同步到数据库。
		em.getTransaction().commit();//提交事务
		em.close();
		fac.close();
	}
	
	@Test
	public void delete(){
		EntityManagerFactory fac=Persistence.createEntityManagerFactory("HelloJPAPU");
		EntityManager em=fac.createEntityManager();
		em.getTransaction().begin();//开启事务
		Person p=em.find(Person.class, 1);
		em.remove(p);//删除托管状态的实体bean
		em.getTransaction().commit();//提交事务
		em.close();
		fac.close();
	}
}