我要评论需求
实体类中有一个 list<string> 类型的属性，对应于 mysql 表里的 varchar 字段，使用 mybatis 添加或查询时能互相转换。
解决方案
自定义一个类型处理器：
package com.examples.handler;
import org.apache.ibatis.type.basetypehandler;
import org.apache.ibatis.type.jdbctype;
import java.sql.callablestatement;
import java.sql.preparedstatement;
import java.sql.resultset;
import java.sql.sqlexception;
import java.util.arraylist;
import java.util.arrays;
import java.util.list;
public class liststringtypehandler extends basetypehandler<list<string>> {
@override
public void setnonnullparameter(preparedstatement ps, int i, list<string> parameter, jdbctype jdbctype) throws sqlexception {
ps.setstring(i, string.join(",", parameter));
}
@override
public list<string> getnullableresult(resultset rs, string columnname) throws sqlexception {
if (rs.getstring(columnname) == null) {
return new arraylist<>();
}
return arrays.aslist(rs.getstring(columnname).split(","));
}
@override
public list<string> getnullableresult(resultset rs, int columnindex) throws sqlexception {
if (rs.getstring(columnindex) == null) {
return new arraylist<>();
}
return arrays.aslist(rs.getstring(columnindex).split(","));
}
@override
public list<string> getnullableresult(callablestatement cs, int columnindex) throws sqlexception {
if (cs.getstring(columnindex) == null) {
return new arraylist<>();
}
return arrays.aslist(cs.getstring(columnindex).split(","));
}
}
示例
java 实体类
@data
public class student {
private long id;
private string name;
private list<string> hobbies;
}
数据表的字段
mapper接口
public interface studentmapper {
void savestudent(student student);
student querystudentbyid(long id);
}
xml文件 需要使用 typehandler="com.examples.handler.liststringtypehandler"
<?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.examples.mapper.studentmapper">
<resultmap id="studentmap" type="student">
<result column="hobbies" property="hobbies" typehandler="com.examples.handler.liststringtypehandler"/>
</resultmap>
<insert id="savestudent" keyproperty="id" usegeneratedkeys="true" keycolumn="id">
insert into student (name, hobbies)
values (#{name}, #{hobbies,typehandler=com.examples.handler.liststringtypehandler})
</insert>
<select id="querystudentbyid" resulttype="student" resultmap="studentmap">
select *
from student
where id = #{id}
</select>
</mapper>
测试
public class studenttest {
@resource
private studentmapper studentmapper;
// 添加
@test
void testsavestudent() {
student student = new student();
list<string> hobbieslist = new arraylist<>();
hobbieslist.add("篮球");
hobbieslist.add("阅读");
hobbieslist.add("写代码");
student.setname("张三");
student.sethobbies(hobbieslist);
studentmapper.savestudent(student);
}
//查询
@test
void testquerystudentbyid() {
student student = studentmapper.querystudentbyid(1l);
system.out.println(student);
}
}
添加的结果
查询的结果
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