mybatis递归 一对多的实现方法示例

前言

今天需要做一个功能，根据专业，有不同的章节，章节下面有对应的习题，

由于只有这么两级，可以不用使用递归，直接查询父集，之后foreach查询子集放入对应的list集合。

虽然实现了，感觉毕竟，太low。

有同事跟我说可以使用mybatis的递归实现，就学习了下。

对应的bean里面需要有对应的list<bean> lists的引用。

直接上代码

对应的sql语句

create table `goods_category` (
 `goodscateid` int(11) not null auto_increment,
 `name` varchar(255) default null,
 `parentid` int(11) default null,
 `description` varchar(255) default null,
 `displayorder` int(11) default null,
 `commissionrate` double default null,
 `enabled` int(11) default null,
 primary key (`goodscateid`)
) engine=innodb auto_increment=11 default charset=utf8;

/*data for the table `goods_category` */
insert into `goods_category`(`goodscateid`,`name`,`parentid`,`description`,`displayorder`,`commissionrate`,`enabled`) values (1,'java',0,'111',null,null,null),(2,'spring',1,'222',null,null,null),(3,'springmvc',1,'333',null,null,null),(4,'struts',1,'444',null,null,null),(5,'jdbc',0,'555',null,null,null),(6,'hibernate',5,'666',null,null,null),(7,'mybatis',5,'777',null,null,null),(8,'jdbctemplate',5,'888',null,null,null),(9,'beanfactory',3,'999',null,null,null),(10,'factorybean',3,'000',null,null,null);

实体类

@jsonignoreproperties({"displayorder","commissionrate","enabled"})
public class goodscategoryvo {
 private integer goodscateid;
 private string name;
 private integer parentid;
 private string description;
 private integer displayorder;
 private double commissionrate;
 private integer enabled;
 private list<goodscategoryvo> catelist;
get 。。。 set。。。 tostring。。。

dao层

public interface goodsmapper {
 list<goodscategoryvo> getcategory(integer pid);
}

mapper.xml

<resultmap id="getself" type="com.bscc.beans.goodscategoryvo">
  <id column="goodscateid" property="goodscateid"></id>
  <result column="name" property="name"></result>
  <collection property="catelist" select="getcategory"
   column="goodscateid"></collection>
  <!--查到的cid作为下次的pid -->
 </resultmap>

 <select id="getcategory" resultmap="getself">
  select * from goods_category where parentid=#{pid}
  order by displayorder,goodscateid
 </select>

之后直接访问对应的方法，即可查询出来

@requestmapping("/getgoodslist")
 @responsebody
 public list<goodscategoryvo> getgoodslist(){
  // pid指定为0
  list<goodscategoryvo> list = goodsmapper.getcategory(0);
  return list;
 }

结果，可以使用 ，也可以使用

[
 {
  "goodscateid": 1,
  "name": "java",
  "parentid": 0,
  "description": "111",
  "catelist": [
   {
    "goodscateid": 2,
    "name": "spring",
    "parentid": 1,
    "description": "222",
    "catelist": []
   },
   {
    "goodscateid": 3,
    "name": "springmvc",
    "parentid": 1,
    "description": "333",
    "catelist": [
     {
      "goodscateid": 9,
      "name": "beanfactory",
      "parentid": 3,
      "description": "999",
      "catelist": []
     },
     {
      "goodscateid": 10,
      "name": "factorybean",
      "parentid": 3,
      "description": "000",
      "catelist": []
     }
    ]
   },
   {
    "goodscateid": 4,
    "name": "struts",
    "parentid": 1,
    "description": "444",
    "catelist": []
   }
  ]
 },
 {
  "goodscateid": 5,
  "name": "jdbc",
  "parentid": 0,
  "description": "555",
  "catelist": [
   {
    "goodscateid": 6,
    "name": "hibernate",
    "parentid": 5,
    "description": "666",
    "catelist": []
   },
   {
    "goodscateid": 7,
    "name": "mybatis",
    "parentid": 5,
    "description": "777",
    "catelist": []
   },
   {
    "goodscateid": 8,
    "name": "jdbctemplate",
    "parentid": 5,
    "description": "888",
    "catelist": []
   }
  ]
 }
]

mybatis递归就是这么的简单。

说下mybatis一对多实现

对应的bean

public class dept {
 private integer id;
 private string deptname;
 private string locadd;
 private list<emp> emps

@jsonignoreproperties("dept")
public class emp {
 private integer id;
 private string name;
 private dept dept;

dao层

public interface deptmapper {
 public dept getdeptbyid(integer id);
}

public interface empmapper {
 public emp getempbydeptid(integer deptid); 
}

mapper.xml文件

<mapper namespace="com.bscc.mapper.deptmapper">
 <resultmap id="deptresultmap" type="com.bscc.beans.dept">
 <id property="id" column="id"/>
 <result property="deptname" column="deptname"/>
 <result property="locadd" column="locadd"/>
 <!-- private list<emp> emps; column="id"写被集合对象主键，select按照外键键查询，通过deptid查出emp给dept--> 
 <collection property="emps" column="id" oftype="emp" select="com.bscc.mapper.empmapper.getempbydeptid"/>
 </resultmap>
 <select id="getdeptbyid" parametertype="integer" resultmap="deptresultmap">
  select * from tbl_dept where id=#{id}
 </select>
</mapper>

<mapper namespace="com.bscc.mapper.empmapper">
 <resultmap id="empresultmap" type="com.bscc.beans.emp">
 <id property="id" column="id"/>
 <result property="name" column="name"/>
 </resultmap>
 <select id="getempbydeptid" parametertype="integer" resultmap="empresultmap">
 select * from tbl_emp where deptid=#{deptid}
 </select>
</mapper>

对应的controller方法

@requestmapping("/getdeptbyid")
 @responsebody
 public dept getdeptbyid() {
  dept deptbyid = deptmapper.getdeptbyid(1);
  return deptbyid;
 }

无非就是比简单查询复杂一些罢了。

代码目录

ok！！！

对应的github地址

https://github.com/chywx/mavenproject6onetomany （本地下载）

总结

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