一对多关联关系

一对多关联关系

<?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.hous.day5.classMapper">
<!--
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,student WHERE class.c_id=student.class_id AND class.c_id=#{id}
SELECT * FROM class,student,teacher WHERE class.c_id=student.class_id AND class.teacher_id=teacher.t_id  AND class.c_id=1
注意：映射关系要按照顺序，和javabean的属性对应
-->
<select id="getClass" parameterType="int" resultMap="classResultMap">
SELECT * FROM class,student,teacher WHERE class.c_id=student.class_id
AND class.teacher_id=teacher.t_id  AND class.c_id=#{id}
</select>
<resultMap type="com.hous.day5.Classes" id="classResultMap">
<id property="id" column="c_id"/>
<result property="name" column="c_name"/>
<association property="teacher" javaType="com.hous.day5.Teacher">
<id property="id" column="t_id"/>
<result property="name" column="t_name"/>
</association>
<collection property="students" ofType="com.hous.day5.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="getClass2" parameterType="int" resultMap="classResultMap2">
SELECT * FROM class WHERE c_id=#{id}
</select>
<select id="getTeacher" parameterType="int" resultType="com.hous.day5.Teacher">
SELECT t_id id, t_name name FROM teacher WHERE t_id=#{id}
</select>
<select id="getStudents" parameterType="int" resultType="com.hous.day5.Student">
SELECT s_id id, s_name name FROM student WHERE class_id=1
</select>
<resultMap type="com.hous.day5.Classes" id="classResultMap2">
<id property="id" column="c_id"/>
<result property="name" column="c_name"/>
<association property="teacher" column="teacher_id" select="getTeacher">
<id property="id" column="t_id"/>
<result property="name" column="t_name"/>
</association>
<collection property="students" column="c_id" select="getStudents">
<id property="id" column="s_id"/>
<result property="name" column="s_name"/>
</collection>
</resultMap>

</mapper>

<?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>

<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<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="root" />
</dataSource>
</environment>
</environments>

<mappers>
<mapper resource="com/hous/day5/classMapper.xml" />
</mappers>
</configuration>

package com.hous.day5;

import static org.junit.Assert.*;

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;

public class MyTest {

private SqlSessionFactory factory = null;

@Before
public void setUp() throws Exception {
String resource = "day5/config.xml";
InputStream config = MyTest.class.getClassLoader().getResourceAsStream(resource);
factory = new SqlSessionFactoryBuilder().build(config);
}

@Test
public void testGetClass() {
SqlSession session = factory.openSession();
String statement = "com.hous.day5.classMapper.getClass2";
Classes classes = session.selectOne(statement, 1);
session.commit();
session.close();
System.out.println("查询结果：" + classes);
}

}

package com.hous.day5;

import java.util.List;

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

public Classes() {
super();
}

public Classes(int id, String name, Teacher teacher) {
super();
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;
}

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

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

/* (non-Javadoc)
* @see java.lang.Object#toString()
*/
@Override
public String toString() {
return "Classes [id=" + id + ", name=" + name + ", teacher=" + teacher + ", students=" + students + "]";
}

}

package com.hous.day5;

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.hous.day5;

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 + "]";
}

}

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),('xs_B',1),('xs_C',1),('xs_D',2),('xs_E',2),('xs_F',2);