012.ResultMap结果映射

1.对ResultMap结果映射的理解

 

 

 2.流程操作

2.1 在good.xml中编辑代码（利用Map接收关联查询结果）

<!-- 利用LinkedHashMap保存多表关联结果
        MyBatis会将每一条记录包装为LinkedHashMap对象
        key是字段名  value是字段对应的值 , 字段类型根据表结构进行自动判断
        优点: 易于扩展,易于使用
        缺点: 太过灵活,无法进行编译时检查
     -->
    <select id="selectGoodsMap" resultType="java.util.LinkedHashMap" flushCache="true">
        select g.* , c.category_name,'1' as test from t_goods g , t_category c
        where g.category_id = c.category_id
    </select>

2.1.1测试代码

 /**
     * 利用Map接收关联查询结果
     * @throws Exception
     */
    @Test
    public void testSelectGoodsMap() throws Exception {
        SqlSession session = null;
        try{
            session = MyBatisUtils.openSession();
            List<Map> list = session.selectList("goods.selectGoodsMap");
            for(Map map : list){
                System.out.println(map);
            }
        }catch (Exception e){
            throw e;
        }finally {
            MyBatisUtils.closeSession(session);
        }
    }

 

2.2 创建dto（dto是一个特殊的Java  Bean叫做数据传输对象，对原始的对象进行扩展，用于数据保存和传递）

package com.imooc.mybatis.dto;

import com.imooc.mybatis.entity.Category;
import com.imooc.mybatis.entity.Goods;
//Data Transfer Object--数据传输对象
public class GoodsDTO {
    private Goods goods = new Goods();
    private Category category = new Category();
    private String test;

    public Goods getGoods() {
        return goods;
    }

    public void setGoods(Goods goods) {
        this.goods = goods;
    }

    public Category getCategory() {
        return category;
    }

    public void setCategory(Category category) {
        this.category = category;
    }

    public String getTest() {
        return test;
    }

    public void setTest(String test) {
        this.test = test;
    }
}

2.3 针对dto对象，如何让Mybatis自动为其进行对应赋值呢？需要使用resultMap结果映射

<select id="selectGoodsDTO" resultMap="rmGoods">
    select g.* , c.*,'1' as test from t_goods g , t_category c
    where g.category_id = c.category_id
</select>

<!--结果映射-->
<resultMap id="rmGoods" type="com.imooc.mybatis.dto.GoodsDTO">
    <!--设置主键字段与属性映射-->
    <!--指定主键：  property是属性名指向了dto中某一个属性的具体名称，column是查询结果中某个字段的名字-->
    <id property="goods.goodsId" column="goods_id"/>
    <!--设置非主键字段与属性映射-->
    <result property="goods.title" column="title"/>
    <result property="goods.originalCost" column="original_cost"/>
    <result property="goods.currentPrice" column="current_price"/>
    <result property="goods.discount" column="discount"/>
    <result property="goods.isFreeDelivery" column="is_free_delivery"/>
    <result property="goods.categoryId" column="category_id"/>
    <result property="category.categoryId" column="category_id"/>
    <result property="category.categoryName" column="category_name"/>
    <result property="category.parentId" column="parent_id"/>
    <result property="category.categoryLevel" column="category_level"/>
    <result property="category.categoryOrder" column="category_order"/>
    <result property="test" column="test"/></resultMap>

2.4 在某个博客看到的一张图片

 

 2.5测试语句

  /**
     * 利用ResultMap进行结果映射
     * @throws Exception
     */
    @Test
    public void testSelectGoodsDTO() throws Exception {
        SqlSession session = null;
        try{
            session = MyBatisUtils.openSession();
            List<GoodsDTO> list = session.selectList("goods.selectGoodsDTO");
            for (GoodsDTO g : list) {
                System.out.println(g.getGoods().getTitle());
            }
        }catch (Exception e){
            throw e;
        }finally {
            MyBatisUtils.closeSession(session);
        }
    }

3.准备工作

3.1 创建Category.java

package com.imooc.mybatis.entity;

public class Category {
    private Integer categoryId;
    private String categoryName;
    private Integer parentId;
    private Integer categoryLevel;
    private Integer categoryOrder;

    public Integer getCategoryId() {
        return categoryId;
    }

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

    public String getCategoryName() {
        return categoryName;
    }

    public void setCategoryName(String categoryName) {
        this.categoryName = categoryName;
    }

    public Integer getParentId() {
        return parentId;
    }

    public void setParentId(Integer parentId) {
        this.parentId = parentId;
    }

    public Integer getCategoryLevel() {
        return categoryLevel;
    }

    public void setCategoryLevel(Integer categoryLevel) {
        this.categoryLevel = categoryLevel;
    }

    public Integer getCategoryOrder() {
        return categoryOrder;
    }

    public void setCategoryOrder(Integer categoryOrder) {
        this.categoryOrder = categoryOrder;
    }
}