Mybatis多对多转化为一对多查询，简单易学(SSM框架)

<?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">

//命名空间为dao的路径

</resultMap>

<select id=" getseller" resultType="Seller">
select * from seller where id=#{id}

</select>

//把多对多转化为一对多（增加一个中间表，详细见下图），根据子查询得到gtype表数据，对应上面select="getgtype"

<select id=" getgtype" resultType="Gtype">
select * from gtype where id in (select typeid from goodstype where goodsid =#{id} )

</select>

//返回类型须写成goodsmap，这样就会自动调用goodsmap中的查询，把查询到的gtype,seller自动放到实体类中

<select id="getAll" resultMap=" goodsmap">
select * from goods
</select>

</mapper>

！------------------------------------------------------------------------------------------------------------------------------------------------------！

实体类Goods，其他两个没啥特别的就不给大家贴了，主要就是定义一个List<Gtype> gtype;

public class Goods {
   Integer id;
    String name;
    String pic;
    Seller seller;
    double price;
    double wprice;//折扣价
    String remark;//备注
    State state;
    Timestamp addtime;
    Integer sort;
    List<Gtype> gtype;


   public Integer getId() {
       return id;
   }
   public void setId(Integer id) {
       this.id = id;
   }
   public Integer getSort() {
       return sort;
   }
   public void setSort(Integer sort) {
       this.sort = sort;
   }
   public String getName() {
       return name;
   }
   public void setName(String name) {
       this.name = name;
   }
   public String getPic() {
       return pic;
   }
   public void setPic(String pic) {
       this.pic = pic;
   }
   public double getPrice() {
       return price;
   }
   public void setPrice(double price) {
       this.price = price;
   }
   public double getWprice() {
       return wprice;
   }
   public void setWprice(double wprice) {
       this.wprice = wprice;
   }
   public String getRemark() {
       return remark;
   }
   public void setRemark(String remark) {
       this.remark = remark;
   }
   public Timestamp getAddtime() {
       return addtime;
   }
   public void setAddtime(Timestamp addtime) {
       this.addtime = addtime;
   }

   public Seller getSeller() {
       return seller;
   }
   public void setSeller(Seller seller) {
       this.seller = seller;
   }

   public State getState() {
       return state;
   }
   public void setState(State state) {
       this.state = state;
   }
   public List<Gtype> getGtype() {
       return gtype;
   }
   public void setGtype(List<Gtype> gtype) {
       this.gtype = gtype;
   }
}

Mybatis多对多转化为一对多查询，简单易学(SSM框架)

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