mybatis xml多表查询，子查询，连接查询，动态sql

小谭の努力2024-01-20 17:09

项目结构

数据库表

student_type 表

student 表

依赖

<dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.30</version>
        </dependency>

        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.5</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>

实体类

Student 类

一个学生只有一个年级

package com.tmg.domain;

public class Student {
    private int id;
    private String name;
    private int age;
    private String email;
    private Integer typeId;
    private Type type;

    public Integer getTypeId() {
        return typeId;
    }

    public void setTypeId(Integer typeId) {
        this.typeId = typeId;
    }

    public Type getType() {
        return type;
    }

    public void setType(Type type) {
        this.type = type;
    }

    public Student(int id, String name, int age, String email) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.email = email;
    }

    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 int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                ", email='" + email + '\'' +
                ", typeId=" + typeId +
//                ", type=" + type +
                '}';
    }
}

Type 类

一个年级有多个学生，所以用 list

package com.tmg.domain;

import java.util.List;

public class Type {
    private Integer id;
    private String name;
    private List<Student> students;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public List<Student> getStudents() {
        return students;
    }

    public void setStudents(List<Student> students) {
        this.students = students;
    }

    @Override
    public String toString() {
        return "Type{" +
                "id=" + id +
                ", name='" + name + '\'' +
//                ", students=" + students +
                '}';
    }
}

StudentDao

package com.tmg.dao;

import com.tmg.domain.Student;
import org.apache.ibatis.annotations.Param;

import java.util.List;

public interface StudentDao {


    //多个参数的配置
    void insertEmp( @Param("stuName")  String name,
                   @Param("stuAge") int age, @Param("stuEmail")  String email);

    List<Student> selectByStudent(Student student);

    void update(Student employee);

    void update2(Student employee);

    List<Student> selectByIds(@Param("ids") int []id);
//    List<Student> selectById(int id);

    List<Student> selectByTypeId(int id);
    List<Student> selectAll();
}

TypeDao

package com.tmg.dao;

import com.tmg.domain.Type;

import java.util.List;

public interface TypeDao {

    List<Type> selectAll();

    Type  selectById(Integer id);
}

mybatis-config.xml配置数据源，日志等

<?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>
<!--    dddd-->
    <settings>
        <setting name="mapUnderscoreToCamelCase" value="ture"/><!--配置下划线转换为驼峰命名风格-->
        <setting name="logImpl" value="STDOUT_LOGGING"/>
    </settings>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"></transactionManager><!--事务管理器-->
            <dataSource type="POOLED"><!--数据源 POOLED代表池化-->
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?serverTimezone=UTC&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="dao/StudentDao.xml"></mapper>
        <mapper resource="dao/TypeDao.xml"></mapper>
    </mappers>
</configuration>

TypeDao.xml

下列代码中：
1 resultMap 里面property对应实体类属性，column对应数据库字段名
2 主键用 id 标签 其他用result
3 关联查询(子查询和连接查询) 连接查询查一次
4 一个年级多个学生，所以用collection 如果一对一用association

<?xml version="1.0" encoding="UTF-8" ?>

<!--指定约束文件：定义和限制当前文件中可以使用的标签和属性，以及标签出现的顺序
mybatis-3-mapper.dtd 约束文件名称
-->
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.tmg.dao.TypeDao">
    <resultMap id="typeMap" type="com.tmg.domain.Type">
        <id property="id" column="type_id"></id>
        <result property="name" column="type_name"></result>
<!--        连接查询-->
<!--        <collection property="students"-->
<!--                    javaType="java.util.List" ofType="com.tmg.domain.Student">-->
<!--            <id property="id" column="stu_id" javaType="java.lang.Integer"></id>-->
<!--            <result property="name" column="stu_name"></result>-->
<!--            <result property="age" column="stu_age"></result>-->
<!--            <result property="email" column="stu_email"></result>-->
<!--        </collection>-->

<!--        子查询-->
        <collection property="students" column="type_id"
                    javaType="java.util.List" ofType="com.tmg.domain.Student"
                    select="com.tmg.dao.StudentDao.selectByTypeId">

        </collection>
<!-- property 实体类中的属性名 column 子查询使用的字段 javaType 集合类型  ofType 集合里面的泛型类型-->
    </resultMap>
    <select id="selectAll" resultMap="typeMap">
        select s.*,t.* from student s join student_type t on s.type_id=t.type_id
    </select>

    <select id="selectById" resultMap="typeMap">
        select * from student_type where type_id=#{id}
    </select>


</mapper>

StudentDao.xml

动态sql不理解可看以下博客：
https://blog.csdn.net/weixin_57689217/article/details/135707991?csdn_share_tail={"type"%3A"blog"%2C"rType"%3A"article"%2C"rId"%3A"135707991"%2C"source"%3A"weixin_57689217"}

<?xml version="1.0" encoding="UTF-8" ?>

<!--指定约束文件：定义和限制当前文件中可以使用的标签和属性，以及标签出现的顺序
mybatis-3-mapper.dtd 约束文件名称
-->
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--映射的命名空间 = 包名+接口类-->
<mapper namespace="com.tmg.dao.StudentDao">
    <!--配置insert操作 id是方法名 parameterType是参数类型  #{属性名}用于读取对象的属性值-->
    <!--#{}和${}的区别，#{}相当于PreparedStatement的占位符？提前编译，避免SQL注入 ${}是Statement字符串拼接，不能避免注入 -->
    <!--获得最新的自增主键值 useGeneratedKeys=true keyProperty主键的属性-->
    <insert id="insert" useGeneratedKeys="true" keyProperty="id">
        insert into student( id,name,age,email) values (#{id},#{name},#{age},#{email});
    </insert>

<!--    问题：查询出的名称为多个单词的字段出现null值-->
<!--    原因：数据库的字段单词以下划线分隔，Java的属性以驼峰命名，导致部分名称不一致无法实现映射-->
    <select id="selectAll" resultMap="student">
        select * from student
    </select>

    <resultMap id="student" type="com.tmg.domain.Student">
        <!--配置主键 property是java属性名 column是表字段名-->
        <id property="id" column="stu_id" javaType="java.lang.Integer"></id>
        <!--普通字段-->
        <result property="name" column="stu_name"></result>
        <result property="age" column="stu_age"></result>
        <result property="email" column="stu_email"></result>
        <result property="typeId" column="type_id"></result>

<!--        <association property="type"-->
<!--                     javaType="com.tmg.domain.Type">-->
<!--            <id property="id" column="type_id"></id>-->
<!--            <result property="name" column="type_name"></result>-->
<!--        </association>-->
        <association property="type" column="type_id"
                     javaType="com.tmg.domain.Type"
                     select="com.tmg.dao.TypeDao.selectById">

        </association>
    </resultMap>


<!--    动态sql-->
<sql id="mySelect">
    select * from student
</sql>
    <select id="selectByStudent" parameterType="com.tmg.domain.Student" resultType="com.tmg.domain.Student" resultMap="student">
        <include refid="mySelect"></include>
        <where>
            <if test="name !=null">

                stu_name like "%"#{name}"%"
            </if>
            <if test="age !=null and age!=0">
                and stu_age=#{age}
            </if>
            <if test="email !=null">
                and stu_email=#{email}
            </if>
        </where>
    </select>

    <update id="update">
        update student
        <set>
            <if test="age !=null and age!=0">
                stu_age=#{age},
            </if>
            <if test="email!=null">
                stu_email=#{email},
            </if>
            <if test="name">
                stu_name=#{name},
            </if>
        </set>
        where stu_id=#{id};
    </update>
    <update id="update2">
        update student
        <trim prefix="set" suffixOverrides=",">
            <if test="age !=null and age!=0">
                stu_age=#{age},
            </if>
            <if test="email!=null">
                stu_email=#{email},
            </if>
            <if test="name">
                stu_name=#{name},
            </if>
        </trim>
        where stu_id=#{id};
    </update>

    <select id="selectByIds" resultMap="student">
        select s.*,t.* from student s join student_type t on s.type_id=t.type_id
        where stu_id in
        <foreach collection="ids" item="id" separator="," open="(" close=")" index="1">
            #{id}
        </foreach>
    </select>

    <select id="selectByTypeId" resultMap="student">
        <include refid="mySelect"></include> where type_id=#{id}
    </select>



</mapper>

TypeDaoText 测试类

package com.tmg.dao;

import com.tmg.domain.Type;
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.Test;

import java.io.IOException;
import java.util.List;

public class TypeDaoText {
    @Test
    public void testselectAll() throws IOException {
        SqlSessionFactory build = new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("mybatis-config.xml"));
        SqlSession sqlSession = build.openSession();
        TypeDao mapper = sqlSession.getMapper(TypeDao.class);
        List<Type> typeList = mapper.selectAll();
        for (Type type : typeList) {
            System.out.println(type);
        }
    }


    @Test
    public void testselectById() throws IOException {
        SqlSessionFactory build = new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("mybatis-config.xml"));
        SqlSession sqlSession = build.openSession();
        TypeDao mapper = sqlSession.getMapper(TypeDao.class);
        Type type = mapper.selectById(1);
        System.out.println(type);
    }
}

StudentDaoText 测试类

package com.tmg.dao;

import com.tmg.domain.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.Test;

import java.io.IOException;
import java.util.List;

public class StudentDaoText {

    @Test
    public void testinsertEmp() throws IOException {
        SqlSessionFactoryBuilder factoryBuilder = new SqlSessionFactoryBuilder();
        SqlSessionFactory factory = factoryBuilder.build(Resources.getResourceAsStream("mybatis-config.xml"));
        SqlSession sqlSession = factory.openSession();
        StudentDao mapper = sqlSession.getMapper(StudentDao.class);
        mapper.insertEmp("tmg",18,"tmg@qq.com");
        sqlSession.commit();
    }

    @Test
    public void testselectByStudent() throws IOException {
        SqlSessionFactory build = new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("mybatis-config.xml"));
        SqlSession sqlSession = build.openSession();
        StudentDao mapper = sqlSession.getMapper(StudentDao.class);
        Student student = new Student();
//        student.setName("z");
//        student.setAge(18);
//        student.setEmail("tmg@qq.com");
        List<Student> students = mapper.selectByStudent(student);
        for (Student student1 : students){
            System.out.println(student1);
        }
    }
    @Test
    public void testupdate() throws IOException {
        //创建会话工厂构建器
        SqlSessionFactoryBuilder factoryBuilder = new SqlSessionFactoryBuilder();
        SqlSessionFactory build = factoryBuilder.build(Resources.getResourceAsStream("mybatis-config.xml"));
        //创建会话
        SqlSession sqlSession = build.openSession();
        //获得Mapper对象
        StudentDao mapper = sqlSession.getMapper(StudentDao.class);
        Student student = new Student();
//        student.setName();
        student.setId(1);
        student.setAge(22);
        mapper.update(student);
        sqlSession.commit();
    }
    @Test
    public void testupdate2() throws IOException {
        SqlSessionFactoryBuilder factoryBuilder = new SqlSessionFactoryBuilder();
        SqlSessionFactory build = factoryBuilder.build(Resources.getResourceAsStream("mybatis-config.xml"));
        SqlSession sqlSession = build.openSession();
        StudentDao mapper = sqlSession.getMapper(StudentDao.class);
        Student student = new Student();
        student.setId(1);
        student.setAge(44);
        mapper.update2(student);
        sqlSession.commit();
    }

    @Test
    public void testselectByIds() throws IOException {
        SqlSessionFactory build = new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("mybatis-config.xml"));
        SqlSession sqlSession = build.openSession();
        StudentDao mapper = sqlSession.getMapper(StudentDao.class);
        int []a={1};
        List<Student> students = mapper.selectByIds(a);
        for (Student student:students){
            System.out.println(student);
            System.out.println(student.getType());
        }
    }
    @Test
    public void testselectAll() throws IOException {
        SqlSessionFactory build = new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("mybatis-config.xml"));
        SqlSession sqlSession = build.openSession();
        StudentDao mapper = sqlSession.getMapper(StudentDao.class);
        List<Student> students = mapper.selectAll();
        for(Student student : students){
            System.out.println(student);
            System.out.println(student.getType());
        }

    }
}
相关推荐
路在脚下@38 分钟前
spring boot的配置文件属性注入到类的静态属性
java·spring boot·sql
北辰浮光5 小时前
[spring]XML配置文件标签
xml·spring
Sunyanhui16 小时前
牛客网 SQL36查找后排序
数据库·sql·mysql
Mitch3118 小时前
【漏洞复现】CVE-2021-45788 SQL Injection
sql·web安全·docker·prometheus·metersphere
网络安全King8 小时前
网络安全 - SQL Injection
sql·web安全·php
Stanford_110610 小时前
高级的SQL查询技巧有哪些？
sql·微信小程序·twitter·微信开放平台
wlyang66612 小时前
1. SQL常见笔试题目
数据库·sql
smilejingwei13 小时前
SQL,生成指定时间间隔内的事件次序号
数据库·sql·spl·esprocspl
张伯毅15 小时前
Flink SQL 支持 kafka 开启 kerberos 权限控制.
sql·flink·kafka
向阳121815 小时前
mybatis 动态 SQL
数据库·sql·mybatis
热门推荐
01Cube-Studio：开源大模型全链路一站式中台02ARM学习（31）编译器对overlay方式的支持03玄机平台应急响应—webshell查杀04Ubuntu 20.04使用Livox mid 360 测试 FAST_LIO05校验 GPT-4 真实性的三个经典问题：快速区分 GPT-3.5 与 GPT-4，并提供免费测试网站06Docker 夺命连环 15 问07构建高效的广告投放系统：应用架构的设计与实现08基于大语言模型（LLM）的合成数据生成、策展和评估的综述09(欧拉)openEuler系统添加网卡文件配置流程、(欧拉)openEuler系统手动配置ipv6地址流程、(欧拉)openEuler系统网络管理说明10【一文读懂】NTN（非地面网络）技术介绍