【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>

studentMapper.xml

 <?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>

teacherMapper.xml

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