【Mybatis】一对多实例

①创建数据库和表，数据库为mytest，表为teacher和student

DROP TABLE IF EXISTS teacher;
DROP TABLE IF EXISTS student;

CREATE TABLE teacher(
    teacher_id INT PRIMARY KEY auto_increment NOT NULL,
    teacher_name VARCHAR(20)
);

CREATE TABLE student(
    student_id INT PRIMARY KEY auto_increment NOT NULL,
    student_name VARCHAR(20),
    teacher_id INT
);

ALTER TABLE student ADD CONSTRAINT fk_teacher_id FOREIGN KEY (teacher_id) REFERENCES teacher(teacher_id);

INSERT INTO teacher(teacher_name) VALUES ("张三丰");
INSERT INTO teacher(teacher_name) VALUES ("王重阳");
INSERT INTO student(student_name, teacher_id) VALUES ("宋远桥", 1);
INSERT INTO student(student_name, teacher_id) VALUES ("俞莲舟", 1);
INSERT INTO student(student_name, teacher_id) VALUES ("俞岱岩", 1);
INSERT INTO student(student_name, teacher_id) VALUES ("张松溪", 1);
INSERT INTO student(student_name, teacher_id) VALUES ("张翠山", 1);
INSERT INTO student(student_name, teacher_id) VALUES ("殷梨亭", 1);
INSERT INTO student(student_name, teacher_id) VALUES ("莫声谷", 1);

INSERT INTO student(student_name, teacher_id) VALUES ("丹阳子马钰", 2);
INSERT INTO student(student_name, teacher_id) VALUES ("长真子谭处端", 2);
INSERT INTO student(student_name, teacher_id) VALUES ("长生子刘处玄", 2);
INSERT INTO student(student_name, teacher_id) VALUES ("长春子丘处机", 2);
INSERT INTO student(student_name, teacher_id) VALUES ("玉阳子王处一", 2);
INSERT INTO student(student_name, teacher_id) VALUES ("广宁子郝大通", 2);
INSERT INTO student(student_name, teacher_id) VALUES ("清静散人孙不二", 2);

②创建Java工程，导入相应的jar包

③创建配置文件conf.xml和数据库配置文件db.properties

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" 
    "http://mybatis.org/dtd/mybatis-3-config.dtd">
    
<configuration>
    <properties resource="db.properties"></properties>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"></transactionManager>
            <dataSource type="POOLED">
                <property name="driver" value="${driver}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${name}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>
    
    <mappers>
        <mapper resource="org/mybatis/mapping/teacherMapper.xml"/>
        <mapper resource="org/mybatis/mapping/studentMapper.xml"/>
    </mappers>
</configuration>

driver = com.mysql.jdbc.Driver
url = jdbc:mysql://localhost:3306/mytest
name = root
password = root

④创建实体类Teacher和Student

package org.mybatis.domain;

import java.util.List;

public class Teacher {

    private int teacher_id;
    private String teacher_name;
    private List<Student> students;
    
    public int getTeacher_id() {
        return teacher_id;
    }

    public void setTeacher_id(int teacher_id) {
        this.teacher_id = teacher_id;
    }

    public String getTeacher_name() {
        return teacher_name;
    }

    public void setTeacher_name(String teacher_name) {
        this.teacher_name = teacher_name;
    }

    public List<Student> getStudents() {
        return students;
    }

    public void setStudents(List<Student> students) {
        this.students = students;
    }

    @Override
    public String toString() {
        return "[Teacher = teacher_id:" + teacher_id + ", teacher_name:" + teacher_name 
                + ", the number of students:" + students.size() + "]";
    }
    
    
}

package org.mybatis.domain;

public class Student {

    private int student_id;
    private String student_name;
    private Teacher teacher;
    
    public int getStudent_id() {
        return student_id;
    }

    public void setStudent_id(int student_id) {
        this.student_id = student_id;
    }

    public String getStudent_name() {
        return student_name;
    }

    public void setStudent_name(String student_name) {
        this.student_name = student_name;
    }

    public Teacher getTeacher() {
        return teacher;
    }

    public void setTeacher(Teacher teacher) {
        this.teacher = teacher;
    }

    @Override
    public String toString() {
        return "[Student = student_id:" + student_id + ", student_name:" + student_name + 
                ", teacher:" + teacher.getTeacher_name() + "]";
    }
    
    
}

⑤创建sql映射文件studentMapper.xml和teacherMapper.xml

注意比较两者的区别

<?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="org.mybatis.mapping.studentMapper">
    <select id="getStudent" resultMap="getStudentMap">
        select * from teacher t, student s where t.teacher_id=s.teacher_id and s.teacher_id=#{id}
    </select>
    
    <resultMap type="org.mybatis.domain.Student" id="getStudentMap">
        <id column="student_id" property="student_id" />
        <result column="student_name" property="student_name" />
        <association property="teacher" javaType="org.mybatis.domain.Teacher">
            <id column="teacher_id" property="teacher_id"/>
            <result column="teacher_name" property="teacher_name"/>
        </association>
    </resultMap>
</mapper>

<?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="org.mybatis.mapping.teacherMapper">
    <select id="getTeacher" resultMap="getTeacherMap">
        select * from teacher t, student s where t.teacher_id=s.teacher_id and t.teacher_id=#{id}
    </select>
    
    <resultMap type="org.mybatis.domain.Teacher" id="getTeacherMap">
        <id column="teacher_id" property="teacher_id" />
        <result column="teacher_name" property="teacher_name" />
        <collection property="students" ofType="org.mybatis.domain.Student">
            <id column="student_id" property="student_id"/>
            <result column="student_name" property="student_name"/>
        </collection>
    </resultMap>
</mapper>

⑥向配置文件中注册 studentMapper.xml和teacherMapper.xml 文件【已添加，查看第③步】

⑦测试类

package org.mybatis.app;

import java.io.InputStream;
import java.util.List;

import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;
import org.mybatis.domain.Student;
import org.mybatis.domain.Teacher;

public class TestOneToMany {

    SqlSession session;
    
    @Before
    public void beforeLoad() {
        InputStream inputStream = 
                TestOneToMany.class.getClassLoader().getResourceAsStream("conf.xml");
        SqlSessionFactory sqlSessionFactory = 
                new SqlSessionFactoryBuilder().build(inputStream);
        session = sqlSessionFactory.openSession();
    }
    
    @Test
    public void testGetStudents() {
        String statement = "org.mybatis.mapping.studentMapper.getStudent";
        List<Student> studentList = session.selectList(statement, 1);
        for(Student s : studentList) {
            System.out.println(s.getStudent_name() + "的师傅是:" + s.getTeacher().getTeacher_name());
        }
        
        session.close();
    }
    
    @Test
    public void testGetTeacher() {
        String statement = "org.mybatis.mapping.teacherMapper.getTeacher";
        Teacher t = session.selectOne(statement, 1);
        System.out.println(t.getTeacher_name() + "有" + t.getStudents().size() + "个徒弟");
        session.close();
    }
    
}

⑧结构图