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象的处理操作

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;
    }
    @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.Driver
url = jdbc:mysql://localhost:3306/mybatis?useSSL=true&useUnicode=true&characterEncoding=utf-8
username = root
password = 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.student
    
    
        
        
        
        
    
    
        select * from mybatis.teacher where id = #{id}
    

测试类

    @Test
    public 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 tname
        from mybatis.student as s, mybatis.teacher as t
        where s.tid = t.id
    
    
    
        
        
        
        
            
            
        
    

测试

@Test
public 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());
    }
}

总结：

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：

Mybatis同时传入多个对象及普通参数

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。

例子：

mapper:

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

xml：

    select 
    
    from student
    where 1 = 1
    
    
        and id = #{student.id}
    
    
    
        and age = #{age}
    

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趣讯吧。