(知识篇)Mybatis02使用（嵌套结果/嵌套查询）(知识篇)Mybatis02使用（嵌套结果/嵌套查询）

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(知识篇)Mybatis02使用（嵌套结果/嵌套查询）

2016年12月25日 18:20:44

阅读数：3289

/**

* MyBatis的嵌套结果/嵌套查询（网上有说这是叫延迟加载）

* 1、一对一：

* 1.1 一对一嵌套结果：实际就是将两个表join起来（参考userMapper.xml的selectUserById方法）

* 得出多行数据，其中，需要用resultMap返回，

* 配置resultMap

* <resultMap type="User" id="selectUserMap" autoMapping="true"></resultMap>

* type：返回的类型的全类名/配置别名

* autoMapping：自动对应字段，如果不写，则需要手动映射起来

* 方法是加入<id column="xxx" property="xxx" />/<result column="xxx" property="xxx"/>

* 1.2 通过 <association> 标签，配置返回的一对一的bean（入User中对应一个Teacher），association中则需要配置Teacher的class

* 例如：<association property="teacher" javaType="Teacher" autoMapping="true"><id column="teacherId" property="id"/><association/>

* 1.3一对一嵌套查询：实际是做两次查询（参考userMapper.xml的selectSingleUserById）

* 和嵌套结果类似：只不过配置association时，需要传入外键，和填写select的语句的id（参考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 为表的外键的列名

* 2、一对多

* 2.1 一对多嵌套结果：跟一对一嵌套结果类似，区别在于（参考teacherMapper.xml的getTeacherByJoin方法）：

* 一对一嵌套结果使用<association>，一对多中使用<collection>标签

* 一对一中使用javaType指定类型，一堆多中使用ofType指定类型；

* resultMap中必须指定id 的标签，否则selectone中返回结果会报错

* 2.2一对多嵌套查询：同样跟一对一嵌套结果类似

* 注意一下collection标签、ofType、指定id标签对应的column

* @param args

测试类：

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的嵌套结果/嵌套查询（网上有说这是叫延迟加载）
*
* 1、一对一：
* 1.1 一对一嵌套结果：实际就是将两个表join起来（参考userMapper.xml的selectUserById方法）
* 得出多行数据，其中，需要用resultMap返回，
* 配置resultMap
* <resultMap type="User" id="selectUserMap" autoMapping="true"></resultMap>
* type：返回的类型的全类名/配置别名
* autoMapping：自动对应字段，如果不写，则需要手动映射起来
* 方法是加入<id column="xxx" property="xxx" />/<result column="xxx" property="xxx"/>
*
* 1.2 通过 <association> 标签，配置返回的一对一的bean（入User中对应一个Teacher），association中则需要配置Teacher的class
* 例如：<association property="teacher" javaType="Teacher" autoMapping="true"><id column="teacherId" property="id"/><association/>
*
*
* 1.3一对一嵌套查询：实际是做两次查询（参考userMapper.xml的selectSingleUserById）
* 和嵌套结果类似：只不过配置association时，需要传入外键，和填写select的语句的id（参考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 为表的外键的列名
*
*
* 2、一对多
* 2.1 一对多嵌套结果：跟一对一嵌套结果类似，区别在于（参考teacherMapper.xml的getTeacherByJoin方法）：
* 一对一嵌套结果使用<association>，一对多中使用<collection>标签
* 一对一中使用javaType指定类型，一堆多中使用ofType指定类型；
* resultMap中必须指定id 的标签，否则selectone中返回结果会报错
* 2.2一对多嵌套查询：同样跟一对一嵌套结果类似
* 注意一下collection标签、ofType、指定id标签对应的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";
/*一对一嵌套结果*/
String selectOneByJoin = userNameSpace+".selectUserById";
User user = session.selectOne(selectOneByJoin,3);
System.out.println(user);
/*一对一嵌套查询*/
String selectOneBySelect = userNameSpace+".selectSingleUserById";
User user2 = session.selectOne(selectOneBySelect,1);
System.out.println(user2);
String teacherNameSpace = "com.mybatis.vo.Teacher";
/*一对多嵌套结果*/
String getTeacherByJoin = teacherNameSpace+".getTeacherByJoin";
Teacher teacher = session.selectOne(getTeacherByJoin,1);
System.out.println(teacher);
/*一对多嵌套查询*/
String getTeacherById = teacherNameSpace+".getTeacherById";
Teacher teacher2 = session.selectOne(getTeacherById,2);
System.out.println(teacher2);
}
}

User类：

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">

<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"/>

</association>
</resultMap>

<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类：

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">

<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>

<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="com/mybatis/vo/userMapper.xml" />
<mapper resource="com/mybatis/vo/teacherMapper.xml" />
</mappers>
</configuration>