表一对多关联（[尚硅谷]_张晓飞_Mybatis 学习笔记四）

CREATE TABLE teacher(
	t_id INT PRIMARY KEY AUTO_INCREMENT, 
	t_name VARCHAR(20)
);
CREATE TABLE class(
	c_id INT PRIMARY KEY AUTO_INCREMENT, 
	c_name VARCHAR(20), 
	teacher_id INT
);
ALTER TABLE class ADD CONSTRAINT fk_teacher_id FOREIGN KEY (teacher_id) REFERENCES teacher(t_id);	

INSERT INTO teacher(t_name) VALUES('LS1');
INSERT INTO teacher(t_name) VALUES('LS2');

INSERT INTO class(c_name, teacher_id) VALUES('bj_a', 1);
INSERT INTO class(c_name, teacher_id) VALUES('bj_b', 2);

CREATE TABLE student(
	s_id INT PRIMARY KEY AUTO_INCREMENT, 
	s_name VARCHAR(20), 
	class_id INT
);
INSERT INTO student(s_name, class_id) VALUES('xs_A', 1);
INSERT INTO student(s_name, class_id) VALUES('xs_B', 1);
INSERT INTO student(s_name, class_id) VALUES('xs_C', 1);
INSERT INTO student(s_name, class_id) VALUES('xs_D', 2);
INSERT INTO student(s_name, class_id) VALUES('xs_E', 2);
INSERT INTO student(s_name, class_id) VALUES('xs_F', 2);

package com.hb.bean;

import java.util.List;

public class Classes {
	private int id;
	private String name;
	private Teacher teacher;
	private List<Student> students;

	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;
	}

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

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

	@Override
	public String toString() {
		return "Classes [id=" + id + ", name=" + name + ", teacher=" + teacher + ", students=" + students + "]";
	}

}

package com.hb.bean;

public class Student {
	private int id;
	private String 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 "Student [id=" + id + ", name=" + name + "]";
	}

}

package com.hb.bean;

public class Teacher {
	private int id;
	private String 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 + "]";
	}
	
	
}

<?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="com.hb.bean.classesMapper">
	<!-- 这里namespace必须是“包名 + xml文件名”，不然要运行的时候要报错 “is not known to the MapperRegistry” -->

	<!-- 方式一: 嵌套结果: 使用嵌套结果映射来处理重复的联合结果的子集 SELECT * FROM class c, teacher t,student 
		s WHERE c.teacher_id=t.t_id AND c.C_id=s.class_id AND c.c_id=1 -->
	<select id="getClass3" parameterType="int" resultMap="ClassResultMap3">
		select * from class c, teacher t,student s where c.teacher_id=t.t_id and
		c.C_id=s.class_id and c.c_id=#{id}
	</select>
	<resultMap type="com.hb.bean.Classes" id="ClassResultMap3">
		<id property="id" column="c_id" />
		<result property="name" column="c_name" />
		<association property="teacher" column="teacher_id"
			javaType="com.hb.bean.Teacher">
			<id property="id" column="t_id" />
			<result property="name" column="t_name" />
		</association>
		<!-- ofType指定students集合中的对象类型 -->
		<collection property="students" ofType="com.hb.bean.Student">
			<id property="id" column="s_id" />
			<result property="name" column="s_name" />
		</collection>
	</resultMap>

	<!-- 方式二：嵌套查询：通过执行另外一个SQL映射语句来返回预期的复杂类型 SELECT * FROM class WHERE c_id=1; 
		SELECT * FROM teacher WHERE t_id=1 //1 是上一个查询得到的teacher_id的值 SELECT * FROM 
		student WHERE class_id=1 //1是第一个查询得到的c_id字段的值 -->
	<select id="getClass4" parameterType="int" resultMap="ClassResultMap4">
		select * from class where c_id=#{id}
	</select>
	<resultMap type="com.hb.bean.Classes" id="ClassResultMap4">
		<id property="id" column="c_id" />
		<result property="name" column="c_name" />
		<association property="teacher" column="teacher_id"
			javaType="com.hb.bean.Teacher" select="getTeacher2"></association>
		<collection property="students" ofType="com.hb.bean.Student" column="c_id"
			select="getStudent"></collection>
	</resultMap>

	<select id="getTeacher2" parameterType="int" resultType="com.hb.bean.Teacher">
		SELECT t_id id, t_name name FROM teacher WHERE t_id=#{id}
	</select>

	<select id="getStudent" parameterType="int" resultType="com.hb.bean.Student">
		SELECT s_id id, s_name name FROM student WHERE class_id=#{id}
	</select>



</mapper>

package com.hb.test3;

import java.io.InputStream;

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 com.hb.bean.Classes;



public class Test3 {

	public static SqlSessionFactory sqlSessionFactory;
	public static SqlSession sqlSession;
	
	@Before
	public void init(){
		//"/"表示是在src根目录下
		String source = "config.xml";
		InputStream inputStream = Test3.class.getClassLoader().getResourceAsStream(source);
		
		try {
			sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
//			sqlSession = sqlSessionFactory.openSession();
			//是否自动提交，默认不是自动提交的
			sqlSession = sqlSessionFactory.openSession(true);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
	
	
	@Test
	public void selectById(){
		String statment = "com.hb.bean.classesMapper.getClass3";
		Classes classes = sqlSession.selectOne(statment, 1);
		System.out.println(classes);
	}
	
	@Test
	public void selectById2(){
		String statment = "com.hb.bean.classesMapper.getClass4";
		Classes classes = sqlSession.selectOne(statment, 1);
		System.out.println(classes);
	}
	
	
}

<?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>

	<settings>
		<!-- changes from the defaults for testing -->
		<setting name="cacheEnabled" value="false" />
		<setting name="useGeneratedKeys" value="true" />
		<setting name="defaultExecutorType" value="REUSE" />
	</settings>

	<environments default="development">
		<environment id="development">
			<transactionManager type="jdbc" />
			<dataSource type="POOLED">
				<!-- 
				<property name="driver" value="oracle.jdbc.driver.OracleDriver"/> 
				<property name="url" value="jdbc:oracle:thin:@192.168.56.201:1521:system"/> 
				-->
				<property name="driver" value="com.mysql.jdbc.Driver" />
				<property name="url" value="jdbc:mysql://localhost:3306/mybatis" />
				<property name="username" value="root" />
				<property name="password" value="123456" />
			</dataSource>
		</environment>
	</environments>

	<mappers>
		<mapper resource="com/hb/bean/classesMapper.xml" />
	</mappers>

</configuration>