Mybatis简易项目--＜多对多查询＞学生选课信息的查询

r囧r小猫 2023-09-24 13:04 40阅读 0赞

前言：本次简单实例适合如我一般开始学习mybatis的新手，需要对mybatis有一定基础和实践，掌握基本的类的会话工厂、类的实例化、注解、结果集映射等操作。

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**目录**

1、配置Mybatis依赖以及配置文件

1、pom文件引入相关依赖：

2、mybatis配置文件

3、数据库驱动以及账户密码配置自行解决

2、创建数据库及数据表

1、在MySQL中创建数据表

1、创建学生表

2、创建课程表

3、创建中间表并设置外键

3、编写POJO类

1、Student持久层

2、Course持久层

4、编写工具类

5、编写接口映射文件

1、CourseMapper

2、StudentMapper接口映射

6、编写测试类实现程序功能

7、查询结果

--------------------

## 1、配置Mybatis依赖以及配置文件 ##

### 1、pom文件引入相关依赖： ###

<?xml version="1.0" encoding="UTF-8"?>
    <project xmlns="http://maven.apache.org/POM/4.0.0"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
        <modelVersion>4.0.0</modelVersion>
        <groupId>org.mybatis</groupId>
        <artifactId>JavaEEWork3</artifactId>
        <version>1.0-SNAPSHOT</version>
    
        <properties>
            <maven.compiler.source>16</maven.compiler.source>
            <maven.compilr.target>16</maven.compilr.target>
        </properties>
        <dependencies>
            <dependency>
                <groupId>org.mybatis</groupId>
                <artifactId>mybatis</artifactId>
                <version>3.5.2</version>
            </dependency>
            
            <dependency>
                <groupId>mysql</groupId>
                <artifactId>mysql-connector-java</artifactId>
                <version>8.0.18</version>
            </dependency>
            <dependency>
                <groupId>junit</groupId>
                <artifactId>junit</artifactId>
                <version>4.12</version>
            </dependency>
        </dependencies>
        <build>
            <resources>
                <resource>
                    <directory>src/main/java</directory>
                    <includes>
                        <include>**/*.properties</include>
                        <include>**/*.xml</include>
                    </includes>
                    <filtering>true</filtering>
                </resource>
            </resources>
        </build>
    
    </project>

### 2、mybatis配置文件 ###

<?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>
        
        
        <properties resource="db.properties"/>
        <environments default="development">
            <environment id="development">
                <transactionManager type="JDBC"/>
                
                <dataSource type="POOLED">
                    <property name="driver" value="${mysql.driver}"/>
                    <property name="url" value="${mysql.url}"/>
                    <property name="username" value="${mysql.username}"/>
                    <property name="password" value="${mysql.password}"/>
                </dataSource>
            </environment>
        </environments>
        
        <mappers>
            <mapper class="com.itheima.dao.StudentMapper"/>
            <mapper class="com.itheima.dao.CourseMapper"/>
        </mappers>
    
    </configuration>

### 3、数据库驱动以及账户密码配置自行解决 ###

## 2、创建数据库及数据表 ##

### 1、在MySQL中创建数据表 ###

#### 1、创建学生表 ####

create table Students(
    id int primary key,
    name varchar(20) not null,
    age int not null
    );
    
    
    
    insert into Students(id,name,age) values(1,"小明",19),(2,"小红",20),(3,"小张",21),(4,"小李",20),(5,"小赵",19);

#### 2、创建课程表 ####

create table Course(
    id int primary key auto_increment,
    cname varchar(20) not null,
    cteacher varchar(10) not null,
    cpoint int not null
    );
    
    insert into Course (id,cname,cteacher,cpoint) values(1,"Java程序设计","李小爱",4),(2,"软件工程","张子期",2),(3,"马克思主义理论","吴光许",4),(4,"体育健康","王不易",2);

#### 3、创建中间表并设置外键 ####

create table Course_M(
    id int primary key auto_increment,
    students_id int not null,
    courses_id int not null,
    foreign key(students_id) references Students(id)
    )
    insert into Course_M(id,students_id,courses_id) values(1,1,2),(2,1,4),(3,2,3),(4,2,1);

##  ##

## 3、编写POJO类 ##

### 1、Student持久层 ###

package com.itheima.pojo;
    
    import java.util.List;
    
    public class Student {
            private int id;
            private  String name;
            private int age;
            private List<Course>CourseList;
    
            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 List<Course> getCourseList()
            {
                return CourseList;
            }
            public void  setCourseList(List<Course> CourseList)
            {
                this.CourseList = CourseList;
            }
    
            @Override
            public String toString()
            {
                return "\nStudent [id=" +id+",name="+name+",age="+age+",CourseList="+CourseList+"]";
            }
    
        }

### 2、Course持久层 ###

package com.itheima.pojo;
    public class Course {
        private int id;
        private  String CourseName;
        private String CourseTeacher;
        private int CoursePoint;
        public int  getid()
        {
            return id;
        }
        public void setId(int id)
        {
            this.id=id;
        }
        public String getCourseName()
        {
            return CourseName;
        }
        public void setCourseName(String CourseName)
        {
            this.CourseName=CourseName;
        }
    
        public String getCourseTeacher()
        {
            return CourseTeacher;
        }
        public void setCourseTeacher(String CourseTeacher)
        {
            this.CourseTeacher=CourseTeacher;
        }
    
        public int getCoursePoint()
        {
            return CoursePoint;
        }
        public void setCoursePoint(int CoursePoint)
        {
            this.CoursePoint=CoursePoint;
        }
    
    
    
        @Override
        public String toString()
        {
            return "\nCourse [id="+id+",CourseName="+CourseName+",CourseTeacher="+CourseTeacher+",CoursePoint="+CoursePoint+"]";
        }
    }

## 4、编写工具类 ##

package com.itheima.utils;
    import java.io.Reader;
    import org.apache.ibatis.io.Resources;
    import org.apache.ibatis.session.SqlSession;
    import org.apache.ibatis.session.SqlSessionFactory;
    import org.apache.ibatis.session.SqlSessionFactoryBuilder;
    
    public class Utils {
            private static SqlSessionFactory sqlSessionFactory=null;
            static {
                try {
                    Reader reader= Resources.getResourceAsReader("mybatis-config.xml");
                    sqlSessionFactory=new SqlSessionFactoryBuilder().build(reader);
    
                }
                catch (Exception e)
                {
                    e.printStackTrace();
                }
            }
            public static SqlSession getSession()
            {
                return sqlSessionFactory.openSession();
            }
        }

## 5、编写接口映射文件 ##

### 1、CourseMapper ###

package com.itheima.dao;
    import com.itheima.pojo.Course;
    import org.apache.ibatis.annotations.*;
    
    import java.util.List;
    
    public interface CourseMapper {
        @Select("select* from Course where id in (select  courses_id from Course_M where students_id=#{id})" )
        @Results({@Result(id = true ,column = "id",property ="id" ),
                @Result(column = "cname",property = "CourseName"),
                @Result(column = "cteacher",property = "CourseTeacher"),
                @Result(column = "cpoint",property = "CoursePoint")
    
        })
        List<Course> FindCourseByStudentId(int students_id);
    
    }

### 2、StudentMapper接口映射 ###

package com.itheima.dao;
    import com.itheima.pojo.Student;
    import org.apache.ibatis.annotations.*;
    public interface StudentMapper {
        @Select("select * from Students where id=#{id}")
        @Results({@Result(id = true,column = "id",property = "id"),
        @Result(column = "age",property = "age"),
                @Result(column = "name",property = "name"),
             @Result(column ="id",property ="CourseList",
                     many=@Many(select="com.itheima.dao.CourseMapper.FindCourseByStudentId"))
        })
        Student FindCourseById(int id);
    
    }

## 6、编写测试类实现程序功能 ##

实例化工具类，开启会话，获取映射文件，执行接口中的方法进行查询，提交事务，关闭事务。

查询学号为2的学生信息及其选课信息：

package Test;
    import com.itheima.dao.CourseMapper;
    import com.itheima.dao.StudentMapper;
    import com.itheima.pojo.Course;
    import com.itheima.pojo.Student;
    import com.itheima.utils.Utils;
    import org.apache.ibatis.session.SqlSession;
    import org.junit.After;
    import org.junit.Test;
    
    public class Stu_ClaTest {
        private SqlSession session;
    
        @Test
        public void Test()
        {
            Utils utils=new Utils();
            session=utils.getSession();
            StudentMapper studentMapper=session.getMapper(StudentMapper.class);
            Student student=studentMapper.FindCourseById(2);
            System.out.println(student.toString());
        }
    
        @After
        public  void destory()
        {
            session.commit();
            session.close();
        }
    }

## 7、查询结果 ##

![375bc2fb28dd4fab913a3e0ed6d7027a.png][]

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[375bc2fb28dd4fab913a3e0ed6d7027a.png]: https://img-blog.csdnimg.cn/375bc2fb28dd4fab913a3e0ed6d7027a.png