MYBATIS-PLUS关联查询，一对一、一对多

原文地址：https://www.freesion.com/article/77301045065/

mybatis-plus没有提供关联查询的crud接口，所以本质上还是使用mybatis方法。

一对一

商品表中的classify_id关联商品分类表中的id
返回商品列表数据时数据内包含商品分类信息

service

 /** * 获取商品列表 * * @param form */ @Override public Result goodsList(GoodsDto form) { Page page = new Page(); page.setCurrent(form.getPage()); page.setSize(form.getSize()); IPage<Map> rows = goodsMapper.goodsList(page, form); if (rows != null) { return ResultGenerate.genSuccessResult(rows); } else { return ResultGenerate.genErroResult("商品信息添加失败，请重试！"); } } 

mapper

package com.ozomall.dao; import com.baomidou.mybatisplus.core.mapper.BaseMapper; import com.baomidou.mybatisplus.core.metadata.IPage; import com.baomidou.mybatisplus.extension.plugins.pagination.Page; import com.ozomall.entity.GoodsDto; import org.apache.ibatis.annotations.Mapper; import java.util.Map; @Mapper public interface GoodsMapper extends BaseMapper<GoodsDto> { IPage<Map> goodsList(Page page,GoodsDto form); } 

mapper.xml

需要注意俩个表中如果有重名的字段需要加columnPrefix属性起个别名
sql语句也要使用as起个一样别名

    <resultMap id="goodsMap" type="com.ozomall.vo.GoodsVo"> <id property="id" column="id"></id> <result property="goodsName" column="goods_name"></result> <result property="goodsPrice" column="goods_price"></result> <result property="commentCount" column="comment_count"></result> <result property="sales" column="sales"></result> <result property="classifyId" column="classify_id"></result> <result property="createTime" column="create_time"></result> <result property="status" column="status"></result> <result property="step" column="step"></result> <result property="cover" column="cover"></result> <association property="classify" javaType="com.ozomall.entity.AdminClassifyDto" columnPrefix="classify_"> <id property="id" column="id"></id> <result property="parentId" column="parent_id"/> <result property="classifyLevel" column="classify_level"/> <result property="name" column="name"/> <result property="createTime" column="create_time"/> </association> </resultMap> <select id="goodsList" parameterType="com.ozomall.entity.GoodsDto" resultMap="goodsMap"> select goods.*,admin_classify.*,admin_classify.id as classify_id from goods left join admin_classify on goods.classify_id=admin_classify.id where goods.del=0 <if test="form.goodsName != null"> and goods.goods_name=#{form.goodsName} </if> <if test="form.classifyId != null"> and goods.classify_id=#{form.classifyId} </if> </select> 

返回结果

一对多

商品属性表中的id对应商品属性值表中的goods_attr_id
查询商品属性时包含此商品属性下的所有值

service

 /** * 获取商品属性 * * @param form */ @Override public Result getGoodsAttr(GoodsAttrDto form) { List<GoodsAttrDto> rows = goodsAttrMapper.goodsAttr(null, form); if (rows != null) { return ResultGenerate.genSuccessResult(rows); } else { return ResultGenerate.genErroResult("失败！"); } } 

mapper

package com.ozomall.dao; import com.baomidou.mybatisplus.core.mapper.BaseMapper; import com.baomidou.mybatisplus.extension.plugins.pagination.Page; import com.ozomall.entity.GoodsAttrDto; import org.apache.ibatis.annotations.Mapper; import java.util.List; @Mapper public interface GoodsAttrMapper extends BaseMapper<GoodsAttrDto> { List<GoodsAttrDto> goodsAttr(Page page, GoodsAttrDto form); } 

mapper.xml

注意别名

    <resultMap id="goodsAttrMap" type="com.ozomall.entity.GoodsAttrDto"> <id property="id" column="id"></id> <result property="goodsId" column="goods_id"></result> <result property="name" column="name"></result> <collection property="children" ofType="com.ozomall.entity.GoodsAttrValDto" columnPrefix="children_"> <id property="id" column="id"></id> <result property="goodsAttrId" column="goods_attr_id"></result> <result property="value" column="value"></result> </collection> </resultMap> <select id="goodsAttr" parameterType="com.ozomall.entity.GoodsAttrDto" resultMap="goodsAttrMap"> select goods_attr.*, goods_attr_val.id as children_id, goods_attr_val.goods_attr_id as children_goods_attr_id, goods_attr_val.value as children_value from goods_attr left join goods_attr_val on goods_attr.id=goods_attr_val.goods_attr_id where goods_attr.goods_id=#{form.goodsId} </select> 

返回结果