mysql的ORM

ORM=Object Relationship Database Mapping

对象和关系数据库的映射

简单说，一个对象，对应数据库里的一条记录

1.

根据id返回一个Hero对象

提供方法get(int id)
返回一个Hero对象

package test;

import bean.Hero;

import java.sql.*;
import java.util.ArrayList;
import java.util.List;

public class add
{
    //把一个Hero对象插入到数据库中
    public static void add(Hero h){
        try {
            Class.forName("com.mysql.jdbc.Driver");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        String sql="INSERT INTO hero VALUES (?,?,?,?)";
        //使用try-with-resource的方式自动关闭连接
        try (
                //建立数据库链接
                Connection c= DriverManager.getConnection("jdbc:mysql://localhost:3306/how2java?characterEncoding=utf-8",
                        "root","123456");
                //创建语句
                PreparedStatement ps=c.prepareStatement(sql);
        ){
            ps.setInt(1,h.id);
            ps.setString(2,h.name);
            ps.setFloat(3,h.hp);
            ps.setInt(4,h.damage);
            ps.execute();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
    //把这个Hero对象对应的数据删除掉
    public static void delete(Hero h){
        try {
            Class.forName("com.mysql.jdbc.Driver");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        String sql="DELETE FROM hero where id=?";
        //使用try-with-resource的方式自动关闭连接
        try (
                //建立数据库链接
                Connection c= DriverManager.getConnection("jdbc:mysql://localhost:3306/how2java?characterEncoding=utf-8",
                        "root","123456");
                //创建语句
                PreparedStatement ps=c.prepareStatement(sql);
        ){
            ps.setInt(1,h.id);
            ps.execute();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
    //更新这条Hero对象
    public static void update(Hero h){
        try {
            Class.forName("com.mysql.jdbc.Driver");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        String sql="UPDATE hero SET name=?,hp=?,damage=? WHERE id=?";
        //使用try-with-resource的方式自动关闭连接
        try (
                //建立数据库链接
                Connection c= DriverManager.getConnection("jdbc:mysql://localhost:3306/how2java?characterEncoding=utf-8",
                        "root","123456");
                //创建语句
                PreparedStatement ps=c.prepareStatement(sql);
        ){
            ps.setString(1,h.name);
            ps.setFloat(2,h.hp);
            ps.setInt(3,h.damage);
            ps.setInt(4,h.id);
            ps.execute();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
 //把所有的Hero数据查询出来，转换为Hero对象后，放在一个集合中返回
    public static List<Hero> list(){
        List<Hero> heroes=new ArrayList<>();
        try {
            Class.forName("com.mysql.jdbc.Driver");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        String sql="SELECT * FROM hero ";
        //使用try-with-resource的方式自动关闭连接
        try (
                //建立数据库链接
                Connection c= DriverManager.getConnection("jdbc:mysql://localhost:3306/how2java?characterEncoding=utf-8",
                        "root","123456");
                //创建语句
                PreparedStatement ps=c.prepareStatement(sql);
        ){
            ResultSet rs=ps.executeQuery();
            while (rs.next()){
                Hero h=new Hero();
                h.id=rs.getInt(1);
                h.name=rs.getString(2);
                h.hp=rs.getFloat(3);
                h.damage=rs.getInt(4);
                heroes.add(h);
            }

        }
        catch (SQLException e) {
            e.printStackTrace();
        }
        return heroes;
    }
    public static Hero get(int id){
        Hero h=new Hero();
        try {
            Class.forName("com.mysql.jdbc.Driver");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        String sql="SELECT * FROM hero WHERE id=?";
        //使用try-with-resource的方式自动关闭连接
        try (
                //建立数据库链接
                Connection c= DriverManager.getConnection("jdbc:mysql://localhost:3306/how2java?characterEncoding=utf-8",
                        "root","123456");
                //创建语句
                PreparedStatement ps=c.prepareStatement(sql);
        ){
            ps.setInt(1,id);
          ResultSet rs=ps.executeQuery();
          if (rs.next()){
              h.id=rs.getInt(1);
              h.name=rs.getString(2);
              h.hp=rs.getFloat(3);
              h.damage=rs.getInt(4);
              System.out.println(h.name);
          }

            }
        catch (SQLException e) {
            e.printStackTrace();
        }
        return h;
    }
    public static void main(String[] args) {
        //先导入jar包mysql-connector-java-5.1.39-bin.jar
        //初始化驱动
        List<Hero> list=list();
        System.out.println("Total:"+list.size());
        Hero h=new Hero();
        h.id=5;h.name="大柱";h.hp=1000f;h.damage=3000;
        add(h);
        list=list();
        System.out.println("Total:"+list.size());
        h=get(1);
        h.name="猴子";
        update(h);
        get(1);
        h=get(5);
        delete(h);
        list=list();
        System.out.println(list.size());



}}