Mybatis中多个对象包含同一个对象的处理操作 Mybatis中多个对象包含同一个对

多个对象对应一个对象时，应该如何进行查询？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; }@Overridepublic 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; }@Overridepublic 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

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 getStudents(); //获得全部学生的信息以及对应的老师List 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
1.模拟数据库思想:连表查询
StudentMapper.xml

select * from mybatis.studentselect * from mybatis.teacher where id = #{id}

测试类

@Testpublic void getStudents(){SqlSession sqlSession = MyBatisUtils.getSqlSession(); StudentDao mapper = sqlSession.getMapper(StudentDao.class); List 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

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

测试

@Testpublic void getStudentsTwo(){SqlSession sqlSession = MyBatisUtils.getSqlSession(); StudentDao mapper = sqlSession.getMapper(StudentDao.class); List students = mapper.getStudentsTwo(); for (Student student : students) {System.out.println("学生姓名："+student.getName()+"\t老师姓名："+student.getTeacher().getName()); }}