mybatis 之三：多对多关联查询

MyBatis 本是apache的一个开源项目iBatis,它是一款优秀的持久层框架，它支持定制化 SQL、存储过程以及高级映射。MyBatis 避免了几乎所有的 JDBC 代码和手动设置参数以及获取结果集。MyBatis 可以使用简单的 XML 或注解来配置和映射原生信息，将接口和 Java 的 POJOs(Plain Old Java Objects,普通的 Java对象)映射成数据库中的记录。

学完hibernate关联关系再来学mybatis关联关系你会发现mybatis的关联关系比hibernate的容易很多，今天就给大家分享一些关于mybatis的关联查询。

1.首先resources下面建一个mybatis-config.xml配好需要连接的数据库,我的是mysql数据库

<?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>
    <!--错误日志-->
    <settings>
        <setting name="logImpl" value="LOG4J"/>
    </settings>

    <typeAliases> 
        <!--批量别名定义 -->
        <package name="com.zking.pojo"></package>
    </typeAliases>
    <!--jdbc数据连接池-->
    <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/t204?characterEncoding=utf-8"/>
                <property name="username" value="root"/>
                <property name="password" value="sasa"/>
            </dataSource>
        </environment>
    </environments>
    <!--添加mapper的依赖-->
    <mappers>
        <mapper resource="com/zking/mapper/PersonMapper.xml"></mapper>
    </mappers>

</configuration>

2.在数据库分别建person，city，card三张表，表自己可以随便建。

person人的类

Create Table

CREATE TABLE `person` (
  `pid` varchar(50) NOT NULL,
  `pname` varchar(50) DEFAULT NULL,
  PRIMARY KEY (`pid`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8

city城市类

Create Table

CREATE TABLE `city` (
  `cid` varchar(50) NOT NULL,
  `cname` varchar(50) DEFAULT NULL,
  `pid` varchar(50) DEFAULT NULL,
  PRIMARY KEY (`cid`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8

card中间表

Create Table

CREATE TABLE `card` (
  `cid` varchar(50) DEFAULT NULL,
  `cno` varchar(50) DEFAULT NULL,
  `pid` varchar(50) NOT NULL,
  PRIMARY KEY (`pid`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8

3.在idea里面创建实体类

package com.zking.pojo;

import java.util.List;

/**
 * 人的类
 */
public class person {

    public person() {
    }

    //人对应城市
    private List<city> cityList;

    public List<city> getCityList() {
        return cityList;
    }

    public void setCityList(List<city> cityList) {
        this.cityList = cityList;
    }

    public person(String pid, String pname) {
        this.pid = pid;
        this.pname = pname;
    }

    private String pid;
    private String pname;

    public String getPid() {
        return pid;
    }

    public void setPid(String pid) {
        this.pid = pid;
    }

    public String getPname() {
        return pname;
    }

    public void setPname(String pname) {
        this.pname = pname;
    }
}



package com.zking.pojo;

import java.util.List;

/**
 * 城市的类
 */
public class city {
    public city() {
    }

    //城市对应人
    private List<person> personList;

    public List<person> getPersonList() {
        return personList;
    }

    public void setPersonList(List<person> personList) {
        this.personList = personList;
    }

    public city(String cid, String cname, String pid) {
        this.cid = cid;
        this.cname = cname;
        this.pid = pid;
    }

    private String cid;
    private String cname;
    private String pid;

    public String getCid() {
        return cid;
    }

    public void setCid(String cid) {
        this.cid = cid;
    }

    public String getCname() {
        return cname;
    }

    public void setCname(String cname) {
        this.cname = cname;
    }

    public String getPid() {
        return pid;
    }

    public void setPid(String pid) {
        this.pid = pid;
    }
}






package com.zking.pojo;

/**
 * 中间表
 */
public class card {
    public card() {
    }

    //人的对象
    private person person;
    //城市的对象
    private city city;


    public com.zking.pojo.person getPerson() {
        return person;
    }

    public void setPerson(com.zking.pojo.person person) {
        this.person = person;
    }

    public com.zking.pojo.city getCity() {
        return city;
    }

    public void setCity(com.zking.pojo.city city) {
        this.city = city;
    }

    public card(String cid, String cno, String pid) {
        this.cid = cid;
        this.cno = cno;
        this.pid = pid;
    }

    private String cid;
    private String cno;
    private String pid;

    public String getCid() {
        return cid;
    }

    public void setCid(String cid) {
        this.cid = cid;
    }

    public String getCno() {
        return cno;
    }

    public void setCno(String cno) {
        this.cno = cno;
    }

    public String getPid() {
        return pid;
    }

    public void setPid(String pid) {
        this.pid = pid;
    }
}

4.创建查询接口

package com.zking.mapper;

import com.zking.pojo.person;

import java.util.List;

/**
 *人的类的接口
 */
public interface IPerson {
    /**
     * 查询所有人及他们的选择城市的信息
     */
    public List<person> selectPerson();
}

5.映射实体类对应关系，及语句

<?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.zking.mapper.IPerson">

    <!-- resultMap:映射实体类和字段之间的一一对应的关系 -->
    <resultMap id="selectPersonList" type="person">
        <id column="pid" property="pid"></id>
        <result column="pname" property="pname"></result>

        <!-- 多对多关联映射：collection -->
        <collection property="cityList" ofType="city">
            <id column="cid" property="cid"></id>
            <result column="cname" property="cname"></result>
        </collection>
    </resultMap>

    <select id="selectPerson" resultMap="selectPersonList">
      SELECT p.*,ci.*,ca.`cno` FROM  person p, city ci, card ca
       WHERE  p.`pid`=ca.`pid` AND ci.`cid`=ca.`cid`
    </select>
</mapper>

6.测试类

package com.zking.temp;

import com.zking.mapper.IPerson;
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;

/**
 * 测试类
 */
public class PersonTemp {
    @Test
    public void selectPerson() throws Exception {
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("mybatis-config.xml"));
        SqlSession sqlSession = sqlSessionFactory.openSession();
        IPerson ipm = sqlSession.getMapper(IPerson.class);
        ipm.selectPerson();
        sqlSession.close();
    }
}

mybatis 之三：多对多关联查询

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