1、多对一
1、1环境搭建
数据库
CREATE TABLE teacher (
id INT(10) NOT NULL,
NAME VARCHAR(64) DEFAULT NULL,
PRIMARY KEY (id),
)ENGINE=INNODB DEFAULT CHARSET=utf8;
INSERT INTO teacher (id ,NAME) VALUES (1,'罗老师');
CREATE TABLE student (
id INT(10) NOT NULL,
NAME VARCHAR(64) DEFAULT NULL,
tid INT(10) DEFAULT NULL,
PRIMARY KEY (id),
KEY fktid (tid),
CONSTRAINT fktid FOREIGN KEY (tid) REFERENCES teacher (id)
)
ALTER TABLE student ENGINE=INNODB DEFAULT CHARSET=utf8;
INSERT INTO student (id ,NAME ,tid) VALUES (1,'小明',1);
INSERT INTO student (id ,NAME ,tid) VALUES (2,'小红',1);
INSERT INTO student (id ,NAME ,tid) VALUES (3,'小张',1);
INSERT INTO student (id ,NAME ,tid) VALUES (5,'小罗',1);
MyBatis.xml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>
<settings>
<setting name="logImpl" value="STDOUT_LOGGING"/><!--日记log4j-->
</settings>
<typeAliases>
<package name="com.Google.pojo"/><!--给实体类取别名-->
</typeAliases>
<!--<typeAliases>
<typeAlias type="com.Google.pojo.User" alias="user"/>
</typeAliases>-->
<environments default="development"><!--可以创建多个环境-->
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/><!--加载驱动-->
<property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=false&useUnicode=true&characterEncoding=UTF-8"/><!--连接数据库-->
<property name="username" value="root"/>
<property name="password" value="root"/>
</dataSource>
</environment>
</environments>
<!--注册接口-->
<mappers>
<mapper resource="com/Google/Dao/StudentMapper.xml"/>
<mapper resource="com/Google/Dao/TeacherMapper.xml"/>
</mappers>
</configuration>
1、2编写实体类、
学生·
@Data
public class Student {
private int id;
private String name;
private Teacher teacher;
}
老师·
@Data
public class Teacher {
private int id;
private String name;
}
1、3编写接口方法
public interface StudentMapper {
List<Student> getStudentList();
List<Student> getStudentList1();
}
1、4编写Mapper
<?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="com.Google.Dao.StudentMapper">
<!--按照查询嵌套处理-->
<select id="getStudentList" resultMap="StudentMap">
select * from student
</select>
<resultMap id="StudentMap" type="Student" >
<result property="id" column="id"/>
<result property="name" column="name"/>
<association property="teacher" column="tid" javaType="Teacher" select="getTeacher"/>
</resultMap>
<select id="getTeacher" resultType="Teacher">
select * from teacher
</select>
<!--按照结果嵌套处理-->
<select id="getStudentList1" resultMap="StudentMap1">
select s.id sid,s.name sname,t.name tname
from Student s,Teacher t
where s.tid=t.id
</select>
<resultMap id="StudentMap1" type="Student">
<result property="id" column="sid"/>
<result property="name" column="sname"/>
<association property="teacher" javaType="Teacher" >
<result property="name" column="tname"/>
</association>
</resultMap>
</mapper>
1、5实现
package com.Google.Dao;
import com.Google.pojo.Student;
import com.Google.units.sqlSessionFactory;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import java.util.List;
public class StudentMapperText {
@Test
public void getStudent(){
SqlSession sqlSession = sqlSessionFactory.getsqlSession();
StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
List<Student> studentList = mapper.getStudentList();
for (Student student : studentList) {
System.out.println(student);
}
sqlSession.close();
}
@Test
public void getStudent1(){
SqlSession sqlSession = sqlSessionFactory.getsqlSession();
StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
List<Student> studentList = mapper.getStudentList1();
for (Student student : studentList) {
System.out.println(student);
}
sqlSession.close();
}
}
1、6运行结果
Student(id=1, name=小明, teacher=Teacher(id=0, name=罗老师))
Student(id=2, name=小红, teacher=Teacher(id=0, name=罗老师))
Student(id=3, name=小张, teacher=Teacher(id=0, name=罗老师))
Student(id=4, name=小王, teacher=Teacher(id=0, name=罗老师))
Student(id=5, name=小罗, teacher=Teacher(id=0, name=罗老师))
2、一对多
2、1环境搭建和一对多一样
2、2编写实体类
@Data
public class Student {
private int id;
private String name;
private int tid;
}
@Data
public class Teacher {
private int id;
private String name;
//一个老师拥有多个学生,给老师创建一个学生集合
private List<Student> student;
}
2、3编写接口的方法
public interface TeacherMapper {
Teacher getTeacher(@Param("tid") int id);
Teacher getTeacher1(@Param("tid") int id);
}
2、4编写Mapper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="com.Google.Dao.TeacherMapper">
<!--按结果嵌套查询-->
<select id="getTeacher" resultMap="TeacherStudent">
select s.id sid, s.name sname, t.id tid, t.name tname
from student s,
teacher t
where s.tid = t.id
and t.id = #{tid}
</select>
<resultMap id="TeacherStudent" type="Teacher">
<result property="id" column="tid"/>
<result property="name" column="tname"/>
<!--ofType="" 用于获取集合中泛型的信息-->
<collection property="student" ofType="Student">
<result property="id" column="sid"/>
<result property="name" column="sname"/>
<result property="tid" column="tid"/>
</collection>
</resultMap>
<!--嵌套表查询(子查询)-->
<select id="getTeacher1" resultMap="TeacherStudent1">
select * from teacher where id=#{tid}
</select>
<resultMap id="TeacherStudent1" type="Teacher">
<result property="id" column="id"/>
<collection property="student" javaType="ArrayList" ofType="Student" select="getStudetByID" column="id"/>
</resultMap>
<select id="getStudetByID" resultType="Student">
select * from student where tid=#{tid}
</select>
</mapper>
2、5实现
public class TeacherMapperText {
@Test
public void getTeacher(){
SqlSession sqlSession = sqlSessionFactory.getsqlSession();
TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);
Teacher teacher = mapper.getTeacher(1);
System.out.println(teacher);
sqlSession.close();
}
@Test
public void getTeacher1(){
SqlSession sqlSession = sqlSessionFactory.getsqlSession();
TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);
Teacher teacher1 = mapper.getTeacher1(1);
System.out.println(teacher1);
sqlSession.close();
}
}
2、6运行结果
Teacher(id=1, name=罗老师, student=[Student(id=1, name=小明, tid=1), Student(id=2, name=小红, tid=1), Student(id=3, name=小张, tid=1), Student(id=4, name=小王, tid=1), Student(id=5, name=小罗, tid=1)])
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