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这篇“MyBatis中怎么实现一对多查询和多对一查询”文章的知识点大部分人都不太理解，所以小编给大家总结了以下内容，内容详细，步骤清晰，具有一定的借鉴价值，希望大家阅读完这篇文章能有所收获，下面我们一起来看看这篇“MyBatis中怎么实现一对多查询和多对一查询”文章吧。
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>
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;
}public interface StudentMapper {
List<Student> getStudentList();
List<Student> getStudentList1();
}<?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>
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();
}
}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))
@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;
}public interface TeacherMapper {
Teacher getTeacher(@Param("tid") int id);
Teacher getTeacher1(@Param("tid") int id);
}<?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>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();
}
}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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