一、应用场景

       一个产品(珀莱雅护肤品套装)，由多个小瓶装商品(保湿霜、润肤乳、洗面奶....)构成，我们将用二级树形结构将数据查询出来。

数据结构如下：

{
    "msg":"success",
    "code":0,
    "ProductList":[
        {
            "pid":1,
            "name":"珀莱雅护肤品套装",
            "maketPrice":199,
            "sysModuleList":[
                {
                    "id":1,
                    "moudleName":"保湿霜",
                    "moduleCode":"001"
                },
                {
                    "id":2,
                    "moudleName":"润肤乳",
                    "moduleCode":"002"
                },
                {
                    "id":3,
                    "moudleName":"洗面奶",
                    "moduleCode":"003"
                }
            ]
        },
        {
            "pid":2,
            "name":"玉兰油护肤品套装",
            "maketPrice":299,
            "sysModuleList":[
                {
                    "id":4,
                    "moudleName":"去痕霜",
                    "moduleCode":"004"
                },
                {
                    "id":5,
                    "moudleName":"洁面奶",
                    "moduleCode":"005"
                },
                {
                    "id":6,
                    "moudleName":"皱纹霜",
                    "moduleCode":"006"
                }
            ]
        }
    ]
}

二、代码实现：

1、首先建立产品(ProductEntityVo)和模块(也就是产品下的小商品，SysModuleEntity)的实体

ProductEntityVo：

public class PadProductEntityVo
{
    private Integer pid;

    private String name;

    private Float maketPrice;



    private List<SysModuleEntity> sysModuleList;



    get,set......


}

 SysModuleEntity：

@TableName("sys_module")
public class SysModuleEntity implements Serializable {
	private static final long serialVersionUID = 1L;

	@TableId
	private Integer id;
	/**
	 * 模块名称
	 */
	private String moudleName;
	/**
	 * 模块标识
	 */
	private String moduleCode;


    get,set......
	
}

2、建好实体后建立一对多的xml配置(这里的查询语句是有个中间表做连接查询的。)

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="com.purete.service.mapper.app.ProductDao" >
  <resultMap id="BaseResultMap" type="com.purete.api.entity.app.ProductEntityVo" >
    <id column="pid" property="pid" jdbcType="INTEGER" />
    <result column="name" property="name" jdbcType="VARCHAR" />
    <result column="maket_price" property="maketPrice" jdbcType="REAL" />
    
        <collection property="sysModuleList" ofType="com.purete.api.entity.sys.SysModuleEntity">
            <result column="id" property="id" />
            <result column="moudle_name" property="moudleName" />
            <result column="module_code" property="moduleCode" />
        </collection>
  </resultMap>


   <!--查询语句、自动映射到ProductEntityVo实体中-->
  <select id="queryList" resultMap="BaseResultMap">
    SELECT a.id as pid,a.name,a.maket_price,c.id as id,c.moudle_name,c.module_code from pad_product a,pad_product_module b,sys_module c WHERE a.id=b.goods_id AND b.module_id=c.id
  </select>

</mapper>

3、dao中查询方法

@Mapper
public interface AppPadProductDao
{
    //微信浏览商品信息
    List<PadProductEntityVo> queryList();
}