MyBatis中多对多关系查询案例(三)

1 表结构
因为是多对多关系，所以用到3张表，我们在平时一个公司一个人可能身兼多个职位，而一个位置肯定会有多个人员。所以人员和职位之间就存在了多对多的关系。




多对多的第三张表


2因为使用了是Maven的聚合管理模式。项目结构如下


3 主项目的pom文件内容

<?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>com.zxf</groupId>
  <artifactId>mybatisProject4</artifactId>
  <packaging>pom</packaging>
  <version>1.0-SNAPSHOT</version>
  <modules>
    <module>mybatisProject4-pojo</module>
    <module>mybatisProject4-mapper</module>
    <module>mybatisProject4-service</module>
  </modules>
  <!--对依赖的坐标的版本做集中管理-->
  <properties>
    <junit.version>4.12</junit.version>
    <mybatis.version>3.2.8</mybatis.version>
    <mysql.version>5.1.32</mysql.version>
    <log4j.version>1.2.17</log4j.version>
    <cglib.version>2.2.2</cglib.version>
    <asm.version>3.1</asm.version>
  </properties>
  <dependencyManagement>
    <dependencies>
      <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>${junit.version}</version>
      </dependency>
      <!-- mybatis -->
      <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>${mybatis.version}</version>
      </dependency>
      <dependency>
        <groupId>cglib</groupId>
        <artifactId>cglib</artifactId>
        <version>${cglib.version}</version>
      </dependency>
      <dependency>
        <groupId>asm</groupId>
        <artifactId>asm</artifactId>
        <version>${asm.version}</version>
      </dependency>
      <!--mysql-->
      <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>${mysql.version}</version>
      </dependency>
      <dependency>
        <groupId>log4j</groupId>
        <artifactId>log4j</artifactId>
        <version>${log4j.version}</version>
      </dependency>
    </dependencies>
  </dependencyManagement>
   <build>
     <!--配置资源拷贝插件-->
     <resources>
       <resource>
         <directory>src/main/java</directory>
         <includes>
           <include>**/*.xml</include>
         </includes>
       </resource>
       <resource>
         <directory>src/main/resouces</directory>
         <includes>
           <include>**/*.xml</include>
           <include>**/*.properties</include>
         </includes>
       </resource>
     </resources>
   </build>
</project>

4 pojo类内容

package com.zxf.pojo;

import java.io.Serializable;
import java.util.List;

public class Employee implements Serializable {
    private String emp_no;
    private String emp_name;
    private String dept_id;
    private String emp_gender;
    private String emp_email;
    // 这里假定，员工和工作岗位（角色）是多对多的关系，
    // 每一个员工可有多于一个的工作岗位（角色），每个工作岗位（角色）可有多个员工
    private List<Job> jobs;

    public String getEmp_no() {
        return emp_no;
    }

    public void setEmp_no(String emp_no) {
        this.emp_no = emp_no;
    }

    public String getEmp_name() {
        return emp_name;
    }

    public void setEmp_name(String emp_name) {
        this.emp_name = emp_name;
    }

    public String getDept_id() {
        return dept_id;
    }

    public void setDept_id(String dept_id) {
        this.dept_id = dept_id;
    }

    public String getEmp_gender() {
        return emp_gender;
    }

    public void setEmp_gender(String emp_gender) {
        this.emp_gender = emp_gender;
    }

    public String getEmp_email() {
        return emp_email;
    }

    public void setEmp_email(String emp_email) {
        this.emp_email = emp_email;
    }

    public List<Job> getJobs() {
        return jobs;
    }

    public void setJobs(List<Job> jobs) {
        this.jobs = jobs;
    }
}

package com.zxf.pojo;

import java.io.Serializable;
import java.util.List;

public class Job implements Serializable {
    private String job_id;
    private String job_name;
    private String job_task;

    // 这里假定，员工和工作岗位（角色）是多对多的关系，
    // 每一个员工可有多于一个的工作岗位（角色），每个工作岗位（角色）可有多个员工
    private List<Employee> employees;

    public String getJob_id() {
        return job_id;
    }

    public void setJob_id(String job_id) {
        this.job_id = job_id;
    }

    public String getJob_name() {
        return job_name;
    }

    public void setJob_name(String job_name) {
        this.job_name = job_name;
    }

    public String getJob_task() {
        return job_task;
    }

    public void setJob_task(String job_task) {
        this.job_task = job_task;
    }

    public List<Employee> getEmployees() {
        return employees;
    }

    public void setEmployees(List<Employee> employees) {
        this.employees = employees;
    }
}

5 mapper层
pom.xml文件内容

<?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">
    <parent>
        <artifactId>mybatisProject4</artifactId>
        <groupId>com.zxf</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>
    <artifactId>mybatisProject4-mapper</artifactId>
    <dependencies>
        <dependency>
            <groupId>com.zxf</groupId>
            <version>1.0-SNAPSHOT</version>
            <artifactId>mybatisProject4-pojo</artifactId>
        </dependency>
        <!-- mybatis -->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
        </dependency>
        <!--mysql-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
        </dependency>
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
        </dependency>
    </dependencies>
</project>

log4j内容

log4j.rootCategory=DEBUG,CONSOLE,LOGFILE
log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern=%C %d{YYYY-MM-dd hh:mm:ss} %L %m %n

log4j.appender.LOGFILE=org.apache.log4j.FileAppender
log4j.appender.LOGFILE.File=h://zhang.log
log4j.appender.LOGFILE.Append=true
log4j.appender.LOGFILE.layout=org.apache.log4j.PatternLayout
log4j.appender.LOGFILE.layout.ConversionPattern=%C %m %n  %L

数据库连接信息

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://192.168.0.148:3306/test
jdbc.user=root
jdbc.password=abc

Mybatis核心配置文件
zhangMybatis.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>
    <properties resource="jdbc.properties"/>
    <settings>
        <setting name="logImpl" value="LOG4J"/>
    </settings>
    <typeAliases>
        <package name="com.zxf.pojo"/>
    </typeAliases>

    <!-- default引用environment的id,当前所使用的环境 -->
    <environments default="abc">
        <environment id="abc">
            <transactionManager type="JDBC"></transactionManager>
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driver}"/>
                <property name="url" value="${jdbc.url}"/>
                <property name="username" value="${jdbc.user}"/>
                <property name="password" value="${jdbc.password}"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper class="com.zxf.mapper.EmployeeMapper"></mapper>
        <mapper class="com.zxf.mapper.JobMapper"></mapper>
    </mappers>
</configuration>

mapper层的接口及映射配置文件

package com.zxf.mapper;

import com.zxf.pojo.Employee;

public interface EmployeeMapper {
    Employee selectEmployeeById(String emp_no);
}

<?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.zxf.mapper.EmployeeMapper">
    <resultMap id="employeeResultMap" type="Employee">
        <id property="emp_no" column="emp_no"></id>
        <result property="emp_name" column="emp_name"></result>
        <result property="dept_id" column="dept_id"></result>
        <result property="emp_gender" column="emp_gender"></result>
        <result property="emp_email" column="emp_email"></result>
        <!-- 多对多映射的关键:collection -->
         <collection property="jobs" javaType="ArrayList" column="emp_no"
                     ofType="job" select="com.zxf.mapper.JobMapper.selectJobByEmpId"
                     fetchType="lazy">
             <id property="job_id" column="job_id"></id>
             <result property="job_name" column="job_name"></result>
             <result property="job_task" column="job_task"></result>
         </collection>
    </resultMap>
     <select id="selectEmployeeById" parameterType="string" resultMap="employeeResultMap">
          SELECT * from  employee_basic WHERE emp_no = #{emp_no}
     </select>

    <select id="selectEmployeeByJobId" parameterType="string" resultType="Employee">
        SELECT * from employee_basic where  emp_no IN
        (SELECT emp_no from employee_job WHERE job_id = #{job_id})
    </select>
</mapper>

package com.zxf.mapper;

import com.zxf.pojo.Job;

public interface JobMapper {
    Job  selectJobById(String job_id);
}

<?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.zxf.mapper.JobMapper">
   <select id="selectJobByEmpId" parameterType="string" resultType="job">
       SELECT * from job where
       job_id in (SELECT job_id from employee_job where emp_no=#{emp_no})
   </select>
    <resultMap id="jobResultMap" type="job">
        <id property="job_id" column="job_id" />
        <result property="job_name" column="job_name" />
        <result property="job_task" column="job_task" />
        <!-- 多对多映射的关键:collection -->
        <collection property="employees" javaType="ArrayList"
                    column="job_id" ofType="Employee"
                    select="com.zxf.mapper.EmployeeMapper.selectEmployeeByJobId"
                    fetchType="lazy">
            <id property="emp_no" column="emp_no" />
            <result property="emp_name" column="emp_name" />
            <result property="dept_id" column="dept_id" />
            <result property="emp_gender" column="emp_gender" />
            <result property="emp_email" column="emp_email" />
        </collection>
    </resultMap>
    <select id="selectJobById" parameterType="string" resultMap="jobResultMap">
        SELECT * from job where  job_id = #{job_id}
    </select>
</mapper>

6 service层，这里面就一个基本的测试；来测试我们直接写的多对多关系查询
pom文件

<?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">
    <parent>
        <artifactId>mybatisProject4</artifactId>
        <groupId>com.zxf</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>mybatisProject4-service</artifactId>
    <dependencies>
        <dependency>
            <groupId>com.zxf</groupId>
            <version>1.0-SNAPSHOT</version>
            <artifactId>mybatisProject4-mapper</artifactId>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
        </dependency>

        <dependency>
            <groupId>cglib</groupId>
            <artifactId>cglib</artifactId>
        </dependency>
        <dependency>
            <groupId>asm</groupId>
            <artifactId>asm</artifactId>
        </dependency>

    </dependencies>

</project>

package com.zxf.service;

import com.zxf.mapper.EmployeeMapper;
import com.zxf.pojo.Employee;
import com.zxf.pojo.Job;
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.InputStream;
import java.util.List;

public class Test1 {
    private SqlSessionFactory sqlSessionFactory;
    private SqlSession session;
    private InputStream is;

    private EmployeeMapper employeeMapper;
    @Before  //用于测试方法之前执行。
    public   void init() throws Exception{
        is= Resources.getResourceAsStream("zhangMyBatis.xml");
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
        session=sqlSessionFactory.openSession();
        employeeMapper=session.getMapper(EmployeeMapper.class);
    }
    @After  //用于测试方法之后执行。
    public void destory()throws Exception{
        session.commit();
        session.close();
        is.close();
    }

    @Test
    public void test1(){
        Employee employee = employeeMapper.selectEmployeeById("HW9804");
        System.out.println(employee.getEmp_name());
        List<Job> jobs = employee.getJobs();
        for(Job j:jobs){
            System.out.println(j.getJob_name());
        }
    }


}

员工李莉莉编号为HW9804 的多个职位为

package com.zxf.service;

import com.zxf.mapper.EmployeeMapper;
import com.zxf.mapper.JobMapper;
import com.zxf.pojo.Employee;
import com.zxf.pojo.Job;
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.InputStream;
import java.util.List;

public class Test2 {
    private SqlSessionFactory sqlSessionFactory;
    private SqlSession session;
    private InputStream is;

    private JobMapper jobMapper;

    @Before  //用于测试方法之前执行。
    public   void init() throws Exception{
        is= Resources.getResourceAsStream("zhangMyBatis.xml");
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
        session=sqlSessionFactory.openSession();
        jobMapper=session.getMapper(JobMapper.class);
    }
    @After  //用于测试方法之后执行。
    public void destory()throws Exception{
        session.commit();
        session.close();
        is.close();
    }

    @Test
    public void test1(){
        Job job = jobMapper.selectJobById("2602");
        System.out.println(job.getJob_name());
        System.out.println("****************职位人员*************************");
                List<Employee> employees = job.getEmployees();
        for(Employee e:employees){
            System.out.println(e.getEmp_name());
        }

    }
}

职位编号为2602 下面所包含的员工