1、创建maven工程，搭建mybatis框架环境
mybatis-config.xml配置文件以及db。properties配置
<?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>
<!-- 引入外部配置文件-->
<properties resource="db.properties"/>
<!-- 配置日志文件，注意不要写错-->
<settings>
<!-- 标准日志工厂-->
<setting name="logImpl" value="STDOUT_LOGGING"/>
</settings>
<typeAliases>
<!-- 1、可以给实体类起别名,实体类少使用-->
<!-- <typeAlias type="pojo.User" alias="User"/>-->
<!-- 2、可以给实体类起别名,默认别名为类名首字母小写
若有注解，则以注解为别名-->
<package name="pojo"/>
</typeAliases>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<!-- 连接数据库，数据库使用的是mysql8.0-->
<dataSource type="POOLED">
<property name="driver" value="${driver}"/>
<property name="url" value="${url}"/>
<property name="username" value="${username}"/>
<property name="password" value="${password}"/>
</dataSource>
</environment>
</environments>
<!--注册StudentMapper.xml-->
<mappers>
<mapper class="dao.TeacherMapper"/>
</mappers>
</configuration>
复制代码数据库使用使用MySQL8.0
driver=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://localhost:3306/表名?useSSL=false&allowPublicKeyRetrieval=true&serverTimezone=UTC
username=数据库用户名
password=数据库密码
复制代码pom.xml依赖
<dependencies>
<!-- mysql驱动-->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.11</version>
</dependency>
<!--mybatis所需jar包-->
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.5.2</version>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
</dependency>
</dependencies>
复制代码2、创建stdent和teacher数据表
CREATE TABLE student (
id int NOT NULL AUTO_INCREMENT,
name varchar(20) ，
tid int NULL DEFAULT NULL,
PRIMARY KEY (id) USING BTREE,
INDEX fktid(tid) USING BTREE,
CONSTRAINT fktid FOREIGN KEY (tid) REFERENCES teacher (id) ON DELETE RESTRICT ON UPDATE RESTRICT
)
CREATE TABLE teacher (
id int NOT NULL AUTO_INCREMENT,
name varchar(20) ,
PRIMARY KEY (id) USING BTREE
)
3、创建对应实体类，学生类
package pojo;
public class Student {
private int id;
private String name;
public Student() {
}
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 Student(int id, String name) {
this.id = id;
this.name = name;
}
}
复制代码老师实体类，一个老师对应多个学生
package pojo;
import lombok.Data;
import java.util.List;
public class Teacher {
private int id;
private String name;
//一个老师对应多个学生
List<Student> students;
public List<Student> getStudents() {
return students;
}
public void setStudents(List<Student> students) {
this.students = students;
}
public Teacher(int id, String name, List<Student> students) {
this.id = id;
this.name = name;
this.students = students;
}
public 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;
}
}
复制代码4、创建TeacherMapper接口
package dao;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;
import pojo.Teacher;
public interface TeacherMapper {
//获取老师信息以及该老师对应的所有学生
//方式一、嵌套查询
Teacher getTeacher(@Param("id") int id);
//方式二、子查询
Teacher getTeacher2(@Param("id") int id);
}
复制代码5、创建TeacherMapper.xml配置文件，写入sql语句以及配置
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="dao.TeacherMapper">
<!-- 嵌套查询-->
<select id="getTeacher" resultType="Teacher" resultMap="getTeachers">
select t.id tid,t.name tname,s.name sname,s.id sid
from teacher t,student s
where t.id=s.tid and t.id=#{id}
</select>
<resultMap id="getTeachers" type="Teacher">
<result column="tid" property="id"/>
<result column="tname" property="name"/>
<!--复杂的属性需要单独处理
对象使用association
集合用collection
此处对象为集合，用collection-->
<!-- javaType指定属性类型,集合中泛型使用ofType-->
<collection property="students" ofType="Student">
<result column="sname" property="name"/>
<result column="sid" property="id"/>
</collection>
</resultMap>
<!-- 子查询-->
<select id="getTeacher2" resultMap="getTeacher2" resultType="Teacher">
select * from teacher where id=#{id}
</select>
<resultMap id="getTeacher2" type="Teacher">
<collection property="students" javaType="ArrayList" ofType="Student" select="getStudents" column="id"/>
</resultMap>
<select id="getStudents" resultType="Student">
select * from student where tid=#{tid}
</select>
</mapper>
复制代码6、创建测试类测试
package dao;
import org.apache.ibatis.session.SqlSession;
import pojo.Student;
import pojo.Teacher;
import until.MyBatisUntil;
import java.util.List;
public class Test {
@org.junit.Test
public void test2(){
SqlSession sqlSession = MyBatisUntil.getSqlSession();
TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);
Teacher teacher = mapper.getTeacher(1);
System.out.println(teacher);
sqlSession.close();
}
@org.junit.Test
public void test3(){
SqlSession sqlSession = MyBatisUntil.getSqlSession();
TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);
Teacher teacher = mapper.getTeacher2(1);
System.out.println(teacher);
sqlSession.close();
}
}
复制代码
查询成功
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