mybatis复杂环境搭建-多对一的处理-一对多的处理

news2024/12/28 20:53:40

复杂环境搭建：

1.1建表：

CREATE table teacher(
id int(10) not null,
name varchar(30) default null,
primary key(id)
)engine=InnoDB default charset=utf8mb3;

INSERT INTO teacher (id, name) VALUES (1, '何老师');

create table student(
id int(10) not null,
name varchar(30) default null,
tid int(10) default null,
primary key (id),
key fktid (tid),
constraint fktid foreign key (tid) references teacher (id)
)engine=InnoDB default charset=utf8mb4;

insert into student(id,name,tid) values(1,'小明',1);
insert into student(id,name,tid) values(2,'小红',1);
insert into student(id,name,tid) values(3,'小蓝',1);
insert into student(id,name,tid) values(4,'小白',1);
insert into student(id,name,tid) values(5,'小黑',1);
insert into student(id,name,tid) values(6,'小青',1);

1.2工具类等基本设置：

package com.heerlin.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;

public class MybatisUtils {
    private static SqlSessionFactory sqlSessionFactory;

    static {
        try {
            //创建数据库会话sqlSessionFactory
            String resource = "mybatis-config.xml";
            //输入流
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    // 定义一个公共的静态方法，用于获取 SqlSession 对象
    public static SqlSession getSqlSession() {
        // 打开一个新的 SqlSession 会话
        return sqlSessionFactory.openSession();
    }
}

1.3实体类和接口：

package com.heerlin.dao;

public interface StudentMapper {

}

package com.heerlin.dao;

public interface TeacherMapper {
}

package com.heerlin.pojo;

import lombok.Data;

@Data
public class Student {
    private int id;
    private String name;
    //学生需要关联一个老师
    private Teacher teacher;
}

package com.heerlin.pojo;

import lombok.Data;

@Data
public class Teacher {
    private int id;
    private String name;
}

1.4 编写xml配置文件：（添加到resource里但保证包结构相同）

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.heerlin.dao.StudentMapper">
</mapper>

1.5绑定：

1.6初步测试：

ok初步测试成功：

多对一的处理：

需求：查询所有学生信息，以及对应的老师信息

2.1写接口：

写sql

方式一子查询

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.heerlin.dao.StudentMapper">

    <select id="getStudent" resultMap="StudentTeacher">
        select * from student
    </select>

    <resultMap id="StudentTeacher" type="Student">
        <result property="id" column="id"/>
        <result property="name" column="name"/>
        <!--复杂属性需要单独处理 对象： association 集合： collection-->
        <association property="teacher" column="tid" javaType="Teacher" select="getTeacher"/>
    </resultMap>

    <select id="getTeacher" resultType="Teacher">
        select * from teacher where id = #{id}
    </select>
</mapper>

方式二按照结果嵌套处理：

<!--    按照结果嵌套处理-->
    <select id="getStudent2" resultMap="StudentTeacher2">
        select s.id sid,s.name sname,t.name tname
        from student s,teacher t
        where s.tid=t.id;
    </select>

    <resultMap id="StudentTeacher2" type="Student">
        <result property="id" column="sid"/>
        <result property="name" column="sname"/>
        <association property="teacher" javaType="Teacher">
            <result property="name" column="tname"/>
        </association>
    </resultMap>

测试1：

    @Test
    public void testStudent()
    {
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
        List<Student> studentList=mapper.getStudent();
        for (Student student : studentList) {
            System.out.println(student);
        }
        sqlSession.close();
    }

测试2：

一对多的处理：

一个老师多个学生

方法一：嵌套查询

sql

<!--    案结果嵌套查询-->
    <select id="getTeacher" resultMap="TeacherStudent">
        select s.id sid,s.name sname,t.name tname,t.id tid
        from student s,teacher t
        where s.tid=t.id and t.id=#{tid}
    </select>

    <resultMap id="TeacherStudent" type="Teacher">
        <result property="id" column="tid"/>
        <result property="name" column="tname"/>
        <!--复杂属性需要单独处理 对象： association 集合： collection javaType="" 指定属性的类型
         集合中的泛型信息，我们使用ofType获取
         -->
        <collection property="students" ofType="Student">
            <result property="id" column="sid"/>
            <result property="name" column="snmae"/>
            <result property="tid" column="tid"/>
        </collection>
    </resultMap>

测试：

    @Test
    public void test()
    {
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);
        Teacher teacher = mapper.getTeacher(1);
        System.out.println(teacher);
        sqlSession.close();
    }

结果：

方法二：子查询

加接口：

写sql

     <select id="getTeacher2" resultMap="TeacherStudent2">
         select * from mybatis.teacher where id=#{tid}
     </select>
    
    <resultMap id="TeacherStudent2" type="Teacher">
        <collection property="students" javaType="ArrayList" ofType="Student" select="getStudentByTeacherId" column="id"/>

    </resultMap>
    <select id="getStudentByTeacherId" resultType="Student">
        select *from mybatis.student where tid=#{tid}
    </select>

测试：

    @Test
    public void test2()
    {
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);
        Teacher teacher = mapper.getTeacher2(1);
        System.out.println(teacher);
        sqlSession.close();
    }

结果：