/**
* MyBatis的嵌套結果/嵌套查詢（網上有說這是叫延遲加載）
*
* 1、一對一：
* 1.1 一對一嵌套結果：實際就是將兩個表join起來（參考userMapper.xml的selectUserById方法）
* 得出多行數據，其中，需要用resultMap返回，
* 配置resultMap
* <resultMap type="User" id="selectUserMap" autoMapping="true"></resultMap>
* type：返回的類型的全類名/配置別名
* autoMapping：自動對應字段，如果不寫，則需要手動映射起來
* 方法是加入<id column="xxx" property="xxx" />/<result column="xxx" property="xxx"/>
*
* 1.2 通過 <association> 標籤，配置返回的一對一的bean（入User中對應一個Teacher），association中則需要配置Teacher的class
* 例如：<association property="teacher" javaType="Teacher" autoMapping="true"><id column="teacherId" property="id"/><association/>
*
*
* 1.3一對一嵌套查詢：實際是做兩次查詢（參考userMapper.xml的selectSingleUserById）
* 和嵌套結果類似：只不過配置association時，需要傳入外鍵，和填寫select的語句的id（參考selectSingleUser方法）
* 例如：<association javaType="Teacher" property="teacher" column="teacherId" select="selectSingleUser" autoMapping="true"></association>
* 其中需要提及一下的是column 爲表的外鍵的列名
*
*
* 2、一對多
* 2.1 一對多嵌套結果：跟一對一嵌套結果類似，區別在於（參考teacherMapper.xml的getTeacherByJoin方法）：
* 一對一嵌套結果使用<association>，一對多中使用<collection>標籤
* 一對一中使用javaType指定類型，一堆多中使用ofType指定類型；
* resultMap中必須指定id 的標籤，否則selectone中返回結果會報錯
* 2.2一對多嵌套查詢：同樣跟一對一嵌套結果類似
* 注意一下collection標籤、ofType、指定id標籤對應的column
*
*
* @param args
*/
測試類：
package com.mybatis.test;
import java.io.InputStream;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import com.mybatis.vo.Teacher;
import com.mybatis.vo.User;
public class Test {
/**
* MyBatis的嵌套結果/嵌套查詢（網上有說這是叫延遲加載）
*
* 1、一對一：
* 1.1 一對一嵌套結果：實際就是將兩個表join起來（參考userMapper.xml的selectUserById方法）
* 得出多行數據，其中，需要用resultMap返回，
* 配置resultMap
* <resultMap type="User" id="selectUserMap" autoMapping="true"></resultMap>
* type：返回的類型的全類名/配置別名
* autoMapping：自動對應字段，如果不寫，則需要手動映射起來
* 方法是加入<id column="xxx" property="xxx" />/<result column="xxx" property="xxx"/>
*
* 1.2 通過 <association> 標籤，配置返回的一對一的bean（入User中對應一個Teacher），association中則需要配置Teacher的class
* 例如：<association property="teacher" javaType="Teacher" autoMapping="true"><id column="teacherId" property="id"/><association/>
*
*
* 1.3一對一嵌套查詢：實際是做兩次查詢（參考userMapper.xml的selectSingleUserById）
* 和嵌套結果類似：只不過配置association時，需要傳入外鍵，和填寫select的語句的id（參考selectSingleUser方法）
* 例如：<association javaType="Teacher" property="teacher" column="teacherId" select="selectSingleUser" autoMapping="true"></association>
* 其中需要提及一下的是column 爲表的外鍵的列名
*
*
* 2、一對多
* 2.1 一對多嵌套結果：跟一對一嵌套結果類似，區別在於（參考teacherMapper.xml的getTeacherByJoin方法）：
* 一對一嵌套結果使用<association>，一對多中使用<collection>標籤
* 一對一中使用javaType指定類型，一堆多中使用ofType指定類型；
* resultMap中必須指定id 的標籤，否則selectone中返回結果會報錯
* 2.2一對多嵌套查詢：同樣跟一對一嵌套結果類似
* 注意一下collection標籤、ofType、指定id標籤對應的column
*
*
* @param args
*/
public static void main(String[] args) {
InputStream is = Test.class.getClassLoader().getResourceAsStream("mybatis-config.xml");
System.out.println(is);
SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(is);
System.out.println(sessionFactory);
SqlSession session = sessionFactory.openSession();
System.out.println(session);
String userNameSpace = "com.mybatis.vo.User";
/*一對一嵌套結果*/
String selectOneByJoin = userNameSpace+".selectUserById";
User user = session.selectOne(selectOneByJoin,3);
System.out.println(user);
/*一對一嵌套查詢*/
String selectOneBySelect = userNameSpace+".selectSingleUserById";
User user2 = session.selectOne(selectOneBySelect,1);
System.out.println(user2);
String teacherNameSpace = "com.mybatis.vo.Teacher";
/*一對多嵌套結果*/
String getTeacherByJoin = teacherNameSpace+".getTeacherByJoin";
Teacher teacher = session.selectOne(getTeacherByJoin,1);
System.out.println(teacher);
/*一對多嵌套查詢*/
String getTeacherById = teacherNameSpace+".getTeacherById";
Teacher teacher2 = session.selectOne(getTeacherById,2);
System.out.println(teacher2);
}
}
User類：
package com.mybatis.vo;
public class User {
private int id;
private String userName;
private int sex;
private Teacher teacher;
public User() {
super();
// TODO Auto-generated constructor stub
}
public User(int id, String userName, int sex, Teacher teacher) {
super();
this.id = id;
this.userName = userName;
this.sex = sex;
this.teacher = teacher;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getUserName() {
return userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
public int getSex() {
return sex;
}
public void setSex(int sex) {
this.sex = sex;
}
public Teacher getTeacher() {
return teacher;
}
public void setTeacher(Teacher teacher) {
this.teacher = teacher;
}
@Override
public String toString() {
return "User [id=" + id + ", userName=" + userName + ", sex=" + sex + ", teacher=" + teacher + "]";
}
}
userMapper.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="com.mybatis.vo.User">
<!-- 一對一嵌套結果 -->
<select id="selectUserById" parameterType="int" resultMap="selectUserMap">
SELECT user.id,userName,sex,teacher.id AS teacherId,teacherName FROM USER
LEFT OUTER JOIN Teacher ON Teacher.id = user.teacherId
where user.id = #{id}
</select>
<resultMap type="User" id="selectUserMap" autoMapping="true">
<!-- <id property="id" column="id"/>
<result property="userName" column="userName"/>
<result property="sex" column="sex"/> -->
<association property="teacher" javaType="Teacher" autoMapping="true">
<id column="teacherId" property="id"/>
<!-- <result column="teacherName" property="teacherName"/> -->
</association>
</resultMap>
<!-- 一對一嵌套查詢 -->
<select id="selectSingleUserById" parameterType="int" resultMap="selectSingleUserMap" >
select * from User where id = #{id}
</select>
<select id="selectSingleUser" parameterType="int" resultType="Teacher">
select * from Teacher where id = #{id}
</select>
<resultMap type="User" id="selectSingleUserMap" autoMapping="true">
<association javaType="Teacher" property="teacher" column="teacherId" select="selectSingleUser" autoMapping="true"></association>
</resultMap>
</mapper>Teacher類：
package com.mybatis.vo;
import java.util.List;
public class Teacher {
private int id;
private String teacherName;
private List<User> users;
public Teacher() {
super();
// TODO Auto-generated constructor stub
}
public Teacher(int id, String teacherName, List<User> users) {
super();
this.id = id;
this.teacherName = teacherName;
this.users = users;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getTeacherName() {
return teacherName;
}
public void setTeacherName(String teacherName) {
this.teacherName = teacherName;
}
public List<User> getUsers() {
return users;
}
public void setUsers(List<User> users) {
this.users = users;
}
@Override
public String toString() {
return "Teacher [id=" + id + ", teacherName=" + teacherName + ", users=" + users + "]";
}
}
teacherMapper.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="com.mybatis.vo.Teacher">
<!-- 嵌套結果 -->
<select id="getTeacherByJoin" parameterType="int" resultMap="getTeacherByJoinMap">
SELECT teacher.*,user.id AS userId,user.UserName,user.Sex FROM Teacher
LEFT OUTER JOIN USER ON user.TeacherID = teacher.id where teacher.id = #{id}
</select>
<resultMap type="Teacher" id="getTeacherByJoinMap" autoMapping="true">
<id column="id" property="id"/>
<collection property="users" ofType="User" autoMapping="true">
<id property="id" column="userId"/>
</collection>
</resultMap>
<!-- 一對多嵌套查詢 -->
<select id="getTeacherById" parameterType="int" resultMap="getTeacherByIdMap">
select * from Teacher where id = #{id}
</select>
<select id="getUserByTeacherId" parameterType="int" resultType="User">
select * from User where teacherId = #{teacherId}
</select>
<resultMap type="Teacher" id="getTeacherByIdMap" autoMapping="true">
<id column="id" property="id"/>
<collection property="users" column="id" select="getUserByTeacherId" autoMapping="true"></collection>
</resultMap>
</mapper>mybatis-config.xml
<?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>
<typeAliases>
<typeAlias type="com.mybatis.vo.User" alias="User" />
<typeAlias type="com.mybatis.vo.Teacher" alias="Teacher" />
</typeAliases>
<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://192.168.1.92:3306/test" />
<property name="username" value="root" />
<property name="password" value="root" />
</dataSource>
</environment>
</environments>
<mappers>
<!-- <mapper resource="org/mybatis/example/BlogMapper.xml" /> -->
<mapper resource="com/mybatis/vo/userMapper.xml" />
<mapper resource="com/mybatis/vo/teacherMapper.xml" />
</mappers>
</configuration>
