MyBatis關聯查詢：多對多（XML實現）

數據表

注：

• 藉助中間表的時候，需要創建中間表，不借助中間的話就不需要創建中間表了
• 建議使用不借助中間表的方式

項目框架搭建

第一步：創建Maven項目

• 添加Maven依賴：

<dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
        <scope>test</scope>
    </dependency>

    <dependency>
        <groupId>log4j</groupId>
        <artifactId>log4j</artifactId>
        <version>1.2.17</version>
    </dependency>

    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <version>1.18.10</version>
    </dependency>

    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>8.0.18</version>
    </dependency>
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.5.4</version>
    </dependency>

• 指定Mapper XML文件在mybatis-config.xml中的配置有效，強制部署resources目錄到classes

<resources>
    <resource>
        <directory>src/main/resources</directory>
        <includes>
            <include>**/*.xml</include>
        </includes>
    </resource>
    <resource>
        <directory>${basedir}/src/main/resources</directory>
    </resource>
</resources>

第二步：配置文件

• log4j.properties

log4j.rootLogger=DEBUG, Console  

#Console
log4j.appender.Console=org.apache.log4j.ConsoleAppender  
log4j.appender.Console.layout=org.apache.log4j.PatternLayout  
log4j.appender.Console.layout.ConversionPattern=%d [%t] %-5p [%c] - %m%n  

log4j.logger.java.sql.ResultSet=INFO  
log4j.logger.org.apache=INFO  
log4j.logger.java.sql.Connection=DEBUG  
log4j.logger.java.sql.Statement=DEBUG  
log4j.logger.java.sql.PreparedStatement=DEBUG  

• mysql.properties

driver=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://127.0.0.1/db_test?useSSL=false&serverTimezone=CST
username=root
password=root

第三步：工具類MyBatisUtil

public class MyBatisUtil {
    private static String CONFIG_FILE_LOCATION = "mybatis-config.xml";
    private static final ThreadLocal<SqlSession> threadLocal = new ThreadLocal<SqlSession>();
    private static SqlSessionFactory sessionFactory;

    static {
        try {
            Reader reader = Resources.getResourceAsReader(CONFIG_FILE_LOCATION);
            SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
            sessionFactory = builder.build(reader);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static SqlSession getSession() {
        SqlSession session = threadLocal.get();
        if (session == null) {
            session = (sessionFactory != null) ? sessionFactory.openSession() : null;
            threadLocal.set(session);
        }
        return session;
    }

    public static void closeSession() {
        SqlSession session = threadLocal.get();
        if (session != null) {
            session.close();
            threadLocal.set(null);
        }
    }
}

藉助中間表實現

實體類

• Course.javat

@Data
@ToString
@AllArgsConstructor
@NoArgsConstructor
public class Course implements Serializable {
    
    private static final long serialVersionUID = -6376901343663894314L;
    
    private Integer id;
    private String name;
    private String intro;

}

• Stu

@Data
@ToString
@AllArgsConstructor
@NoArgsConstructor
public class Stu implements Serializable {

    private static final long serialVersionUID = 1765918887138569106L;

    private Integer id;
    private String name;
    private  Boolean gender;

}

第一步：創建mybatis-config.xml

<?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>
    <!--引入外部properties文件  -->
    <properties resource="mysql.properties"></properties>

    <settings>
        <!-- 打印查詢語句 -->
        <setting name="logImpl" value="STDOUT_LOGGING"/>
    </settings>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">  <!-- 數據源的配置，連接到數據庫 -->
                <property name="driver" value="${driver}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>
 
    <mappers>
        <mapper resource="mapper/CourseMapper.xml"/>
        <mapper resource="mapper/StuMapper.xml"/>
    </mappers>
    
</configuration>

注意：mappers標籤中使用的是resouce

第二步：Dao接口

• CourseDao

public interface CourseDao {

    /**
     * 查詢某個學生選擇的所有課程
     */
    List<Course> selectCourseByStuName(String name);
}

• StuDao

public interface StuDao {

    /**
     * 查詢選擇了某門課程的學生
     */
    List<Stu> selectStuByCourseName(String name);
}

第三步：映射文件

• CourseMapper.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="com.hc.dao.CourseDao">
    <select id="selectCourseByStuName" resultType="com.hc.bean.Course" parameterType="string">
        select c.id,c.name,c.intro
        from tb_stu s
        inner join tb_stu_course sc on s.id = sc.stu_id
        inner join tb_course c  on c.id = sc.course_id
        where s.name=#{name}
    </select>
</mapper>

• StuMapper.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="com.hc.dao.StuDao">
    <select id="selectStuByCourseName" resultType="com.hc.bean.Stu" parameterType="string">
        select s.id,s.name,s.gender
        from tb_stu s
        inner join tb_stu_course sc on s.id = sc.stu_id
        inner join tb_course c  on c.id = sc.course_id
        where c.name=#{name}
    </select>
</mapper>

測試代碼

public class CourseStuDaoTest {

    @Test
    public  void  selectStuByCourseName(){
        SqlSession session = MyBatisUtil.getSession();
        CourseDao courseDao = session.getMapper(CourseDao.class);
        List<Course> courseList = courseDao.selectCourseByStuName("zhangsan");
        courseList.forEach(System.out::println);
    }

    @Test
    public  void  selectStuByCourseName(){
        SqlSession session = MyBatisUtil.getSession();
        StuDao stuDao = session.getMapper(StuDao.class);
        List<Stu> stuList = stuDao.selectStuByCourseName("english");
        stuList.forEach(System.out::println);
    }

}

不借助不間表實現

實體類

• Course.javat

@Data
@ToString
@AllArgsConstructor
@NoArgsConstructor
public class Course implements Serializable {
    
    private static final long serialVersionUID = -6376901343663894314L;
    
    private Integer id;
    private String name;
    private String intro;

}

• Stu

@Data
@ToString(exclude = "courses")
@AllArgsConstructor
@NoArgsConstructor
public class Stu {
    private Integer id;
    private String name;
    private  Boolean gender;
    ////////////////////////
    private List<Course> courses ;

}

第一步：創建mybatis-config.xml

<?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>

    <!--引入外部properties文件  -->
    <properties resource="mysql.properties"></properties>

    <settings>
        <!-- 打印查詢語句 -->
        <setting name="logImpl" value="STDOUT_LOGGING"/>
    </settings>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">  <!-- 數據源的配置，連接到數據庫 -->
                <property name="driver" value="${driver}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>
    
    <mappers>
        <mapper resource="mapper/StuMapper.xml"/>
    </mappers>

</configuration>

第二步：創建StuDao接口

public interface StuDao {
    List<Stu> selectStuWithCouseByStuName(String name);
}

第三步：創建映射文件StuMapper.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="com.hc.dao.StuDao">

    <resultMap type="com.hc.bean.Stu" id="resultMap">
        <id column="sid" property="id"/>
        <result column="sname" property="name"/>
        <result column="sgender" property="gender"/>
        <collection property="courses" ofType="com.hc.bean.Course">
            <id column="cid" property="id"/>
            <result column="cname" property="name"/>
            <result column="cintro" property="intro"/>
        </collection>
    </resultMap>

    <select id="selectStuWithCouseByStuName" resultMap="resultMap" parameterType="string">
        SELECT
        tb_stu.id sid,tb_stu.name sname,tb_stu.gender sgender,tb_course.id cid,tb_course.name cname,tb_course.intro cintro
        FROM
        tb_stu
        INNER JOIN tb_stu_course ON tb_stu_course.stu_id = tb_stu.id
        INNER JOIN tb_course ON tb_stu_course.course_id = tb_course.id
        WHERE tb_stu.name=#{name}
    </select>

</mapper>

測試代碼

public class StuDaoTest {

    @Test
    public void selectStuWithCouseByStuName() {
        SqlSession session = MyBatisUtil.getSession();
        StuDao stuDao = session.getMapper(StuDao.class);
        List<Stu> stuList = stuDao.selectStuWithCouseByStuName("lisi");
        System.out.println(stuList);
        for (Stu stu : stuList) {
            stu.getCourses().forEach(System.out::println);
        }
    }


}