Mybatis中多个对象包含同一个对象的处理操作

例如

关键字：association : 联系 ，关联 多个人可以关联一个人。

首先做一些准备,如:实体类,工具类和Mybatis核心文件

实体类：

//老师实体类package com.MLXH.pojo;public class Teacher { private int id; private String name; public Teacher() { } public Teacher(int id, String name) {this.id = id;this.name = name; } public int getId() {return id; } public void setId(int id) {this.id = id; } public String getName() {return name; } public void setName(String name) {this.name = name; } @Override public String toString() {return 'Teacher{' +'id=' + id +', name=’' + name + ’’’ +’}’; }}

//学生实体类package com.MLXH.pojo;public class Student { private int id; private String name; private Teacher teacher; public Student() { } public Student(int id, String name, Teacher teacher) {this.id = id;this.name = name;this.teacher = teacher; } public int getId() {return id; } public void setId(int id) {this.id = id; } public String getName() {return name; } public void setName(String name) {this.name = name; } public Teacher getTeacher() {return teacher; } public void setTeacher(Teacher teacher) {this.teacher = teacher; } @Override public String toString() {return 'Student{' +'id=' + id +', name=’' + name + ’’’ +', teacher=' + teacher +’}’; }}

database.properties配置文件数据库需要的数据

driver = com.mysql.jdbc.Driverurl = jdbc:mysql://localhost:3306/mybatis?useSSL=true&useUnicode=true&characterEncoding=utf-8username = rootpassword = 123456

Mybatis工具类:mybatis-config.xml

<?xml version='1.0' encoding='UTF-8' ?><!DOCTYPE configurationPUBLIC '-//mybatis.org//DTD Config 3.0//EN''http://mybatis.org/dtd/mybatis-3-config.dtd'><configuration> <!--配置文件修改--> <properties resource='database.properties'/> <!--Mybatis设置--> <settings><!--默认日志实现--><!--<setting name='logImpl' value='STDOUT_LOGGING'/>--><!--Log4j实现--><setting name='logImpl' value='LOG4J'/> </settings> <!--配置别名--> <typeAliases><package name='com.MLXH.pojo'/> </typeAliases> <environments default='development'><environment id='development'> <transactionManager type='JDBC'/> <dataSource type='POOLED'><property name='driver' value='${driver}'/><property name='url' value='${url}'/><property name='username' value='${username}'/><property name='password' value='${password}'/> </dataSource></environment> </environments> <mappers><!--class对应的是一个接口类--><!--resource对应的是一个接口类的映射文件--><mapper resource='com/MLXH/dao/StudentMapper.xml'/> </mappers></configuration>

工具类:主要是为了使获得sqlsession更为简单方便

package com.MLXH.utils;import org.apache.ibatis.io.Resources;import org.apache.ibatis.session.SqlSession;import org.apache.ibatis.session.SqlSessionFactory;import org.apache.ibatis.session.SqlSessionFactoryBuilder;import java.io.IOException;import java.io.InputStream;//mybatis的工具类，重复的代码的提纯public class MyBatisUtils { //类变量不需要设置默认值； private static SqlSessionFactory sqlSessionFactory; static {//在maven中，所有的资源文件一般都放在resources目录下，我们可以直接拿到。try { String resource = 'mybatis-config.xml'; InputStream inputStream = Resources.getResourceAsStream(resource); sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);} catch (IOException e) { e.printStackTrace();} } //设置SqlSessionFactory公共的方法 public static SqlSessionFactory getSqlSessionFactory(){return sqlSessionFactory; } //获得一个带事务自动提交功能的SqlSession公共的方法 public static SqlSession getSqlSession(){//自动提交事务return sqlSessionFactory.openSession(true); }}

StudentDao接口

package com.MLXH.dao;import com.MLXH.pojo.Student;import java.util.List;public interface StudentDao { //获得全部学生的信息以及对应的老师 List<Student> getStudents(); //获得全部学生的信息以及对应的老师 List<Student> getStudentsTwo();}

针对于StudentDao接口的实现mapper文件:我们使用如下的方式来进行查询

StudentMapper.xml

<?xml version='1.0' encoding='UTF-8' ?><!DOCTYPE mapperPUBLIC '-//mybatis.org//DTD Mapper 3.0//EN''http://mybatis.org/dtd/mybatis-3-mapper.dtd'><!--namespace不能写别名--><mapper namespace='com.MLXH.dao.StudentDao'> <!--遇到问题：学生类中关联老师： 多个学生对应一个老师 --><!--解决问题方式一:按查询结果嵌套处理，模拟数据库思想；--> <select resultMap='StudentTeacher'>select * from mybatis.student </select> <resultMap type='Student'><id column='id' property='id'/><result column='name' property='name'/><!--属性和字段对应 ， 类和表对应 ， 对象和记录关联一个字段需求：拿到老师这个类的属性association ： 关联，多对一 column ： 数据库对应的列名 property ： 对应属性名 javaType ： 多对一字段对应的Java类型 select ： 关联一个语句--><association column='tid' property='teacher' javaType='Teacher' select='getTeacher'/> </resultMap> <select resultType='Teacher'>select * from mybatis.teacher where id = #{id} </select></mapper>

测试类

@Test public void getStudents(){SqlSession sqlSession = MyBatisUtils.getSqlSession();StudentDao mapper = sqlSession.getMapper(StudentDao.class);List<Student> students = mapper.getStudents();for (Student student : students) { System.out.println('学生姓名：'+student.getName()+'t老师姓名：'+student.getTeacher().getName());} }2.模拟面向对象的思想

<?xml version='1.0' encoding='UTF-8' ?><!DOCTYPE mapperPUBLIC '-//mybatis.org//DTD Mapper 3.0//EN''http://mybatis.org/dtd/mybatis-3-mapper.dtd'><!--namespace不能写别名!!!!!--><mapper namespace='com.MLXH.dao.StudentDao'> <!-- 解决方式二：一个resultMap解决 ， 模拟面向对象的思想--> <select resultMap='StudentTeacher2'>select s.id,s.name,t.id as tid,t.name as tnamefrom mybatis.student as s, mybatis.teacher as twhere s.tid = t.id </select> <!--设置结果集映射ResultMap --> <resultMap type='Student'><id property='id' column='id'/><result property='name' column='name'/><!--直接关联一个老师--><association property='teacher' javaType='Teacher'> <id property='id' column='tid'/> <result property='name' column='tname'/></association> </resultMap></mapper>

测试

@Testpublic void getStudentsTwo(){ SqlSession sqlSession = MyBatisUtils.getSqlSession(); StudentDao mapper = sqlSession.getMapper(StudentDao.class); List<Student> students = mapper.getStudentsTwo(); for (Student student : students) {System.out.println('学生姓名：'+student.getName()+'t老师姓名：'+student.getTeacher().getName()); }}

mybatis中遇到多对一的情况，要使用关联映射处理：使用association

两种处理思路：

当传入多个文件时，mapper接口文件的方法参数要使用@param（“xx”）注释。

mapper:

//Student是对象，age是String类型。int getPojo(@param('student') Student student, @param('age') String age );

xml：

<select resultMap='BaseResultMap'> select <include refid='Base_Column_List' /> from student where 1 = 1 <!-- 使用参数一（是个自己的对象） --> <if test='student.id != null'>and id = #{student.id} </if> <!-- 使用参数二 String类型 --> <if test='age!= null'>and age = #{age} </if></select>

以上为个人经验，希望能给大家一个参考，也希望大家多多支持好吧啦网。