MyBatis数据查询步骤

 第一创建实体类

　　

package com.imooc.mybatis.entity;

public class GoodsEntity {
    private Integer goodsId; //商品编号
    private String title;//标题
    private String subTitle;//子标题
    private Float originalCost;//原价
    private Float currentPrice;//折扣价格
    private Float discount;// 折扣
    private Integer isFreeDelivery;//是否包邮 1-包邮 0-不包邮
    private Integer categoryId;// 分类编号

    public Integer getGoodsId() {
        return goodsId;
    }

    public void setGoodsId(Integer goodsId) {
        this.goodsId = goodsId;
    }

    public String getTilte() {
        return title;
    }

    public void setTilte(String tilte) {
        this.title = tilte;
    }

    public String getSubTitle() {
        return subTitle;
    }

    public void setSubTitle(String subTitle) {
        this.subTitle = subTitle;
    }

    public Float getOriginalCost() {
        return originalCost;
    }

    public void setOriginalCost(Float originalCost) {
        this.originalCost = originalCost;
    }

    public Float getCurrentPrice() {
        return currentPrice;
    }

    public void setCurrentPrice(Float currentPrice) {
        this.currentPrice = currentPrice;
    }

    public Float getDiscount() {
        return discount;
    }

    public void setDiscount(Float discount) {
        this.discount = discount;
    }

    public Integer getIsFreeDelivery() {
        return isFreeDelivery;
    }

    public void setIsFreeDelivery(Integer isFreeDelivery) {
        this.isFreeDelivery = isFreeDelivery;
    }

    public Integer getCategoryId() {
        return categoryId;
    }

    public void setCategoryId(Integer categoryId) {
        this.categoryId = categoryId;
    }
}

第二部  创建Mapper MXL

　　

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

第三步 编写select标签

<mapper namespace="goods">
        <!--根据namespace 加上 id 精确找寻sql语句 -->
        <!--resultType结果类型 goods对象类型 -->
        <select id="findAll" resultType="com.imooc.mybatis.entity.GoodsEntity">
            <!-- 编写sql语句 -->
            SELECT * FROM t_goods ORDER BY goods_id DESC limit 10;
        </select>
</mapper>

开启驼峰命名法

　　在mybatis-config。xml里配置

　　

    <!-- 引入外部properties文件 -->
    <properties resource="datasource.properties"/>


    <settings>
        <!--设置启用数据库字段下划线映射到java对象的驼峰式命名属性，默认为false-->
        <setting name="mapUnderscoreToCamelCase" value="true"/>
    </settings>

第五步 新增mapper

　　

    <mappers>
        <!-- 映射goods。xml -->
        <mapper resource="mappers/goods.xml"></mapper>
    </mappers>

在mybatis-config.xml配置

第六步执行sql

package com.imooc.mybatis.test;

import com.imooc.mybatis.entity.GoodsEntity;
import com.imooc.mybatis.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.sql.Connection;
import java.util.List;

public class SelectTestor {

    @Test
    public void selectAll() throws Exception {
        //调用MybatisUtils工具类获得数据库连接
        SqlSession sqlSession = null;
        try {
            //获取sql对象
            sqlSession = MybatisUtils.openSession();
            //执行sql
            List<GoodsEntity> list = sqlSession.selectList("goods.findAll");
            //查看连接状态
            Connection conn = MybatisUtils.getConnection(sqlSession);

            for (int i = 0; i < list.size(); i++) {
                GoodsEntity goodsEntity =  list.get(i);
                System.out.println(goodsEntity.getTilte()+"---"+goodsEntity.getDiscount());
            }

        }catch (Exception e){
            throw e;
        }finally {
            MybatisUtils.release(sqlSession);
        }
    }
}