package po;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
/**
 * 学生实体类
 * @author 强子
 *
 */
@Entity
public class Student implements java.io.Serializable{
	   @Id
	   @GeneratedValue(strategy=GenerationType.AUTO)//注解生成策略 
	   private Integer id;
	   private String name;
	   private String sex;
	   private int age;
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getSex() {
		return sex;
	}
	public void setSex(String sex) {
		this.sex = sex;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	@Override
	public String toString() {
		return "Student [id=" + id + ", name=" + name + ", sex=" + sex
				+ ", age=" + age + "]";
	}
	   
	   
	   
}

DAO

package dao;

import java.util.List;



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

import po.Student;

public class StudentDaoImpl implements StudentDao{
	@PersistenceContext(unitName="ejb")//依赖注入    读取persistence.xml
    private EntityManager em;
	@Override
	public EntityManager getEntityManager() {
		return em;
	}
	/**
	 * 保存数据
	 */
	@Override
	public void save(Student s) {
		em.persist(s);
	}
    /**
     * 删除数据
     */
	@Override
	public void delete(Student s) {
		//先merge(s)后remove的原因是 穿过的对象已经是脱离管理
		//错误信息 ：java.lang.IllegalArgumentException: Removing a detached instance
		em.remove(em.merge(s));
		em.flush();
		
	}
   /**
    * 根据主键查询
    */
	@Override
	public Student findById(int id) {
		return (Student)em.find(Student.class, id);
	}
    /**
     * 更新数据
     */
	@Override
	public void update(Student s) {
		System.out.println(s);
		em.merge(s);
		em.flush();
	}
	
}