SSM框架学习04——MyBatis关联数据查询
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2024-01-15 23:56:58
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文章目录
一、创建数据库表
1、创建教师表teacher
CREATE TABLE `teacher` (
`t_id` int(11) NOT NULL AUTO_INCREMENT,
`t_name` varchar(20) DEFAULT NULL,
PRIMARY KEY (`t_id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;
INSERT INTO `teacher` VALUES ('1', '刘晓云');
INSERT INTO `teacher` VALUES ('2', '郑同华');
INSERT INTO `teacher` VALUES ('3', '李明军');
2、创建班级表class
CREATE TABLE `class` (
`c_id` int(11) NOT NULL AUTO_INCREMENT,
`c_name` varchar(20) DEFAULT NULL,
`teacher_id` int(11) DEFAULT NULL,
PRIMARY KEY (`c_id`),
KEY `fk_teacher_id` (`teacher_id`),
CONSTRAINT `fk_teacher_id` FOREIGN KEY (`teacher_id`) REFERENCES `teacher` (`t_id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;
INSERT INTO `class` VALUES ('1', '14软件1班', '3');
INSERT INTO `class` VALUES ('2', '13软件2班', '2');
INSERT INTO `class` VALUES ('3', '15软件1班', '1');
3、创建学生表student
CREATE TABLE `student` (
`s_id` int(11) NOT NULL AUTO_INCREMENT,
`s_name` varchar(30) DEFAULT NULL,
`s_gender` varchar(10) DEFAULT NULL,
`s_age` int(11) DEFAULT NULL,
`class_id` int(11) DEFAULT NULL,
PRIMARY KEY (`s_id`)
) ENGINE=InnoDB AUTO_INCREMENT=10 DEFAULT CHARSET=utf8;
INSERT INTO `student` VALUES ('1', '佟大为', '男', '20', '1');
INSERT INTO `student` VALUES ('2', '李方玉', '女', '19', '1');
INSERT INTO `student` VALUES ('3', '郑大林', '男', '19', '2');
INSERT INTO `student` VALUES ('4', '温晓辉', '男', '18', '1');
INSERT INTO `student` VALUES ('5', '吴文静', '女', '19', '2');
INSERT INTO `student` VALUES ('6', '肖文艳', '女', '18', '3');
INSERT INTO `student` VALUES ('7', '杨文军', '男', '20', '3');
INSERT INTO `student` VALUES ('8', '唐雨涵', '女', '19', '2');
INSERT INTO `student` VALUES ('9', '金雨欣', '女', '20', '2');
二、创建实体类
1、教师实体类Teacher
package net.cw.mybatis.bean;
public class Teacher {
private int id;
private String name;
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;
}
@Override
public String toString() {
return "Teacher{" +
"id=" + id +
", name='" + name + '\'' +
'}';
}
}
2、学生实体类Student
package net.cw.mybatis.bean;
public class Student {
private int id;
private String name;
private String gender;
private int age;
private Clazz clazz;
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 String getGender() {
return gender;
}
public void setGender(String gender) {
this.gender = gender;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public Clazz getClazz() {
return clazz;
}
public void setClazz(Clazz clazz) {
this.clazz = clazz;
}
@Override
public String toString() {
return "Student{" +
"id=" + id +
", name='" + name + '\'' +
", gender='" + gender + '\'' +
", age=" + age +
", clazz=" + clazz.getName() +
'}';
}
}
3、班级实体类Clazz
package net.cw.mybatis.bean;
import java.util.List;
public class Clazz{
private int id;
private String name;
private Teacher teacher;
private List<Student> students;
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 Teacher getTeacher() {
return teacher;
}
public void setTeacher(Teacher teacher) {
this.teacher = teacher;
}
public List<Student> getStudents() {
return students;
}
public void setStudents(List<Student> students) {
this.students = students;
}
@Override
public String toString() {
return "Clazz{" +
"id=" + id +
", name='" + name + '\'' +
", teacher=" + teacher +
", students=" + students +
'}';
}
}
三、配置和定义映射文件
1、在mybatis-config.xml文件里配置实体类别名和映射文件：
<?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>
<!--配置实体类别名-->
<typeAliases>
<typeAlias type="net.cw.mybatis.bean.User" alias="User"/>
<typeAlias type="net.cw.mybatis.bean.Clazz" alias="Clazz"/>
<typeAlias type="net.cw.mybatis.bean.Teacher" alias="Teacher"/>
<typeAlias type="net.cw.mybatis.bean.Student" alias="Student"/>
</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://localhost:3306/test_mybatis?characterEncoding=utf8"/>
<property name="username" value="root"/>
<property name="password" value="1"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="mapper/UserMapper.xml"/>
<mapper resource="mapper/ClazzMapper.xml"/>
</mappers>
</configuration>
2、定义班级映射文件ClazzMapper.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="net.cw.mybatis.mapper.ClazzMapper">
<!--三表关联查询-->
<select id="findById" parameterType="Clazz" resultMap="clazzResultMap">
SELECT * FROM teacher INNER JOIN class ON class.teacher_id = teacher.t_id
INNER JOIN student ON class.c_id = student.class_id WHERE c_id = #{id};
</select>
<resultMap id="clazzResultMap" type="Clazz">
<result property="id" column="c_id"/>
<result property="name" column="c_name"/>
<!--一对一-->
<association property="teacher" column="teacher_id" javaType="Teacher">
<result property="id" column="t_id"/>
<result property="name" column="t_name"/>
</association>
<!--一对多-->
<collection property="students" ofType="Student">
<result property="id" column="s_id"/>
<result property="name" column="s_name"/>
<result property="gender" column="s_gender"/>
<result property="age" column="s_age"/>
<association property="clazz" column="class_id" javaType="Clazz">
<result property="name" column="c_name"/>
</association>
</collection>
</resultMap>
<!--###########################################################-->
<!--通过嵌套查询实现一对一关联-->
<select id="findAll" resultMap="clazzResultMap2">
SELECT * FROM class;
</select>
<resultMap id="clazzResultMap2" type="Clazz">
<result property="id" column="c_id"/>
<result property="name" column="c_name"/>
<association property="teacher" column="teacher_id" javaType="Teacher"
select="getTeacher"/>
</resultMap>
<select id="getTeacher" resultType="Teacher">
SELECT t_id id, t_name name FROM teacher WHERE t_id = #{id};
</select>
</mapper>
四、定义班级映射接口ClazzMapper
package net.cw.mybatis.mapper;
import net.cw.mybatis.bean.Clazz;
import java.util.List;
public interface ClazzMapper {
Clazz findById(int id);
List<Clazz> findAll();
}
五、创建测试程序TestClazzMapper
package net.cw.mybatis.mapper;
import net.cw.mybatis.bean.Clazz;
import net.cw.mybatis.bean.Student;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import java.io.IOException;
import java.io.Reader;
import java.util.List;
public class TestClazzMapper {
private SqlSession session;
private ClazzMapper clazzMapper;
@Before
public void init() {
try {
Reader reader = Resources.getResourceAsReader("mybatis-config.xml");
SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(reader);
session = factory.openSession();
clazzMapper = session.getMapper(ClazzMapper.class);
} catch (IOException e) {
e.printStackTrace();
}
}
@Test
public void testFindById() {
Clazz clazz = clazzMapper.findById(1);
System.out.println(clazz);
List<Student> students = clazz.getStudents();
for(Student student : students) {
System.out.println(student);
}
}
@Test
public void testFindAll() {
List<Clazz> clazzes = clazzMapper.findAll();
for (Clazz clazz : clazzes) {
System.out.println(clazz);
}
}
@After
public void destroy() {
session.close();
}
}
1、运行testFindById方法，查看结果
2、运行testFindAll方法，查看结果
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