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Mybatis框架(十)：Mybatis的对象关系映射（一）_mybatis映射创建对象

作者：Gausst松鼠会 | 2024-05-26 06:50:04

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mybatis映射创建对象

一、对象关系映射环境搭建

1、创建数据库表


CREATE DATABASE test;
 
CREATE TABLE `user` (
  `id` int(11) NOT NULL auto_increment,
  `username` varchar(32) NOT NULL COMMENT '用户名称',
  `birthday` datetime default NULL COMMENT '生日',
  `sex` char(1) default NULL COMMENT '性别',
  `address` varchar(256) default NULL COMMENT '地址',
  PRIMARY KEY  (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
 
 
insert  into `user`(`id`,`username`,`birthday`,`sex`,`address`) values (41,'老王','2018-02-27 17:47:08','男','北京');
insert  into `user`(`id`,`username`,`birthday`,`sex`,`address`) values (42,'小二王','2018-03-02 15:09:37','女','北京金燕龙');
insert  into `user`(`id`,`username`,`birthday`,`sex`,`address`) values (43,'小二王','2018-03-04 11:34:34','女','北京金燕龙');
insert  into `user`(`id`,`username`,`birthday`,`sex`,`address`) values (45,'传智播客','2018-03-04 12:04:06','男','北京金燕龙');
insert  into `user`(`id`,`username`,`birthday`,`sex`,`address`) values (46,'老王','2018-03-07 17:37:26','男','北京');
insert  into `user`(`id`,`username`,`birthday`,`sex`,`address`) values (48,'小马宝莉','2018-03-08 11:44:00','女','北京修正');
 
CREATE TABLE `account` (
  `ID` int(11) NOT NULL COMMENT '编号',
  `UID` int(11) default NULL COMMENT '用户编号',
  `MONEY` double default NULL COMMENT '金额',
  PRIMARY KEY  (`ID`),
  KEY `FK_Reference_8` (`UID`),
  CONSTRAINT `FK_Reference_8` FOREIGN KEY (`UID`) REFERENCES `user` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
 
insert  into `account`(`ID`,`UID`,`MONEY`) values (1,46,1000),(2,45,1000),(3,46,2000);

2、创建maven工程并导入坐标

3、创建实体类、持久层dao接口

在domain包中创建User类


package com.wedu.mybatis09.domain;
 
import java.io.Serializable;
import java.util.Date;
import java.util.List;
 
/**
 * 用户实体
 */
public class User implements Serializable {
 
    private Integer id;
    private String username;
    private String address;
    private String sex;
    private Date birthday;
 
    public Integer getId() {
        return id;
    }
 
    public void setId(Integer id) {
        this.id = id;
    }
 
    public String getUsername() {
        return username;
    }
 
    public void setUsername(String username) {
        this.username = username;
    }
 
    public String getAddress() {
        return address;
    }
 
    public void setAddress(String address) {
        this.address = address;
    }
 
    public String getSex() {
        return sex;
    }
 
    public void setSex(String sex) {
        this.sex = sex;
    }
 
    public Date getBirthday() {
        return birthday;
    }
 
    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }
 
    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", address='" + address + '\'' +
                ", sex='" + sex + '\'' +
                ", birthday=" + birthday +
                '}';
    }
}

在domain包中创建Account类


package com.wedu.mybatis09.domain;
 
import java.io.Serializable;
 
/**
 * 账户实体
 */
public class Account implements Serializable {
 
    private Integer id;
    private Integer uid;
    private Double money;
 
    public Integer getId() {
        return id;
    }
 
    public void setId(Integer id) {
        this.id = id;
    }
 
    public Integer getUid() {
        return uid;
    }
 
    public void setUid(Integer uid) {
        this.uid = uid;
    }
 
    public Double getMoney() {
        return money;
    }
 
    public void setMoney(Double money) {
        this.money = money;
    }
 
    @Override
    public String toString() {
        return "Account{" +
                "id=" + id +
                ", uid=" + uid +
                ", money=" + money +
                '}';
    }
}

在dao包中创建IUserDao接口


package com.wedu.mybatis09.dao;
 
/**
 * 用户的持久层接口
 */
public interface IUserDao {
 
}

在dao包中创建IAccountDao接口


package com.wedu.mybatis09.dao;
 
/**
 * 账户持久层接口
 */
public interface IAccountDao {
 
}

4、创建数据库配置文件：jdbc.properties


jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/test?useSSL=true&useUnicode=true&characterEncoding=utf8
jdbc.username=root
jdbc.password=123456

5、创建日志文件：log4j.properties


# Set root category priority to INFO and its only appender to CONSOLE.
#log4j.rootCategory=INFO, CONSOLE            debug   info   warn error fatal
log4j.rootCategory=debug, CONSOLE, LOGFILE
 
# Set the enterprise logger category to FATAL and its only appender to CONSOLE.
log4j.logger.org.apache.axis.enterprise=FATAL, CONSOLE
 
# CONSOLE is set to be a ConsoleAppender using a PatternLayout.
log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern=%d{ISO8601} %-6r [%15.15t] %-5p %30.30c %x - %m\n
 
# LOGFILE is set to be a File appender using a PatternLayout.
log4j.appender.LOGFILE=org.apache.log4j.FileAppender
log4j.appender.LOGFILE.File=E:\\project\\axis.log
log4j.appender.LOGFILE.Append=true
log4j.appender.LOGFILE.layout=org.apache.log4j.PatternLayout
log4j.appender.LOGFILE.layout.ConversionPattern=%d{ISO8601} %-6r [%15.15t] %-5p %30.30c %x - %m\n

6、创建配置文件：SqlMapConfig.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>
    <!--引用外部的配置文件信息-->
    <properties resource="jdbc.properties"/>
 
    <!--配置别名-->
    <typeAliases>
        <package name="com.wedu.mybatis09.domain"/>
    </typeAliases>
 
    <!--配置环境-->
    <environments default="development">
        <environment id="development">
            <!--配置事务的类型-->
            <transactionManager type="JDBC"></transactionManager>
            <!--配置数据源-->
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driver}"/>
                <property name="url" value="${jdbc.url}"/>
                <property name="username" value="${jdbc.username}"/>
                <property name="password" value="${jdbc.password}"/>
            </dataSource>
        </environment>
    </environments>
 
    <!--配置映射文件的位置-->
    <mappers>
        <package name="com.wedu.mybatis09.dao" />
    </mappers>
</configuration>

7、创建测试类UserDaoTest和AccountDaoTest

UserDaoTest测试类


package com.wedu.mybatis09.dao;
 
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;
 
/**
 * 对象关系映射测试
 */
public class UserDaoTest {
 
    private SqlSession session;
    private IUserDao userDao;
 
    @Before
    public void init() throws Exception{
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("SqlMapConfig.xml"));
        session = factory.openSession();
        userDao = session.getMapper(IUserDao.class);
    }
 
    @After
    public void destroy() {
        session.close();
    }
}

AccountDaoTest测试类


package com.wedu.mybatis09.dao;
 
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;
 
public class AccountDaoTest {
 
    private SqlSession session;
    private IAccountDao accountDao;
 
    @Before
    public void init() throws Exception{
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("SqlMapConfig.xml"));
        session = factory.openSession();
        accountDao = session.getMapper(IAccountDao.class);
    }
 
    @After
    public void destroy() {
        session.close();
    }
}


    /**
     * 查询所有账户
     */
    @Test
    public void testFindAll() {
        List<Account> accounts = accountDao.findAll();
        for (Account account : accounts) {
            System.out.println(account);
            System.out.println(account.getUser());
        }
    }

二、mybatis基于XML的对象关系映射的实现

1、创建映射文件：IUserDao.xml和IAccountDao.xml

IUserDao.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.wedu.mybatis09.dao.IUserDao">
 
</mapper>

IAccountDao.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.wedu.mybatis09.dao.IAccountDao">
 
</mapper>

2、一对一的关系映射

2.1、在Account实体类添加User属性


    //一对一的关系映射:从表实体应该包含一个主表实体的对象引用
    private User user;
 
    public User getUser() {
        return user;
    }
 
    public void setUser(User user) {
        this.user = user;
    }

2.2、在IAccountDao中添加查询方法


    /**
     * 查询所有账户,，同时还要获取到当前账户的所属用户信息
     * @return
     */
    List<Account> findAll();

2.3、在IAccountDao.xml添加sql语句


    <!--定义封装account和user的resultMap-->
    <resultMap id="accountUserMap" type="account">
        <id property="id" column="aid"></id>
        <result property="uid" column="uid"></result>
        <result property="money" column="money"></result>
        <!-- 一对一的关系映射：配置封装user的内容-->
        <association property="user" column="uid" javaType="user">
            <id property="id" column="id"></id>
            <result property="username" column="username"></result>
            <result property="birthday" column="birthday"></result>
            <result property="sex" column="sex"></result>
            <result property="address" column="address"></result>
        </association>
    </resultMap>
    <!-- 查询所有 -->
    <select id="findAll" resultMap="accountUserMap">
        select u.*,a.id as aid,a.uid,a.money from account a , user u where u.id = a.uid;
    </select>

2.4、在AccountDaoTest的测试类中测试


    /**
     * 查询所有账户
     */
    @Test
    public void testFindAll() {
        List<Account> accounts = accountDao.findAll();
        for (Account account : accounts) {
            System.out.println(account);
            System.out.println(account.getUser());
        }
    }

3、一对多（多对一）映射

3.1、在User实体类添加Account属性


    //一对多关系映射：主表实体应该包含从表实体的集合引用
    private List<Account> accounts;
 
    public List<Account> getAccounts() {
        return accounts;
    }
 
    public void setAccounts(List<Account> accounts) {
        this.accounts = accounts;
    }

3.2、在IUserDao中添加查询方法


    /**
     * 查询所有用户,，同时获取到用户下所有账户的信息
     * @return
     */
    List<User> findAll();

3.3、在IUserDao.xml添加sql语句


    <!--定义User的resultMap-->
    <resultMap id="userAccountMap" type="user">
        <id property="id" column="id"></id>
        <result property="username" column="username"></result>
        <result property="birthday" column="birthday"></result>
        <result property="sex" column="sex"></result>
        <result property="address" column="address"></result>
        <!--一对多的关系映射：配置user对象中accounts集合的映射-->
        <collection property="accounts" ofType="account">
            <id property="id" column="aid"></id>
            <result property="uid" column="uid"></result>
            <result property="money" column="money"></result>
        </collection>
    </resultMap>
    <!-- 查询所有 -->
    <select id="findAll" resultMap="userAccountMap">
        select u.*,a.id as aid,a.uid,a.money from user u left outer join account a on u.id = a.uid
    </select>

3.4、在UserDaoTest的测试类中测试


    /**
     * 查询所有用户
     */
    @Test
    public void testFindAll() {
        List<User> users = userDao.findAll();
        for (User user : users) {
            System.out.println(user);
            System.out.println(user.getAccounts());
        }
    }

三、mybatis基于注解的对象关系映射的实现

1、一对一的关系映射

1.1、在Account实体类添加User属性


    //一对一的关系映射:从表实体应该包含一个主表实体的对象引用
    private User user;
 
    public User getUser() {
        return user;
    }
 
    public void setUser(User user) {
        this.user = user;
    }

1.2、在IAccountDao接口中添加查询方法并添加一对一的关系映射的注解


    /**
     * 查询所有账户
     * @return
     */
    @Select("select * from account")
    @Results(id = "accountMap",value = {
            @Result(id = true,column = "id",property = "id"),
            @Result(column = "uid",property = "uid"),
            @Result(column = "money",property = "money"),
            @Result(property = "user",column = "uid",one=@One(select="com.wedu.mybatis15.dao.IUserDao.findById",fetchType= FetchType.EAGER))
    })
    List<Account> findAll();

1.3、在IUserDao接口中添加根据id查询方法


    /**
     * 根据id查询用户
     * @param id
     * @return
     */
    @Select("select * from user where id=#{id}")
    User findById(Integer id);

1.4、在AccountDaoTest的测试类中测试


    /**
     * 查询所有账户
     */
    @Test
    public void testFindAll() {
        List<Account> accounts = accountDao.findAll();
        for (Account account : accounts) {
            System.out.println(account);
            System.out.println(account.getUser());
        }
    }

2、一对多（多对一）映射

1.1、在User实体类添加Account属性


    //一对多关系映射：主表实体应该包含从表实体的集合引用
    private List<Account> accounts;
 
    public List<Account> getAccounts() {
        return accounts;
    }
 
    public void setAccounts(List<Account> accounts) {
        this.accounts = accounts;
    }

1.2、在IUserDao接口中添加关联查询方法并添加多对一的关系映射注解


    /**
     * 查询所有用户
     * @return
     */
    @Select("select * from user")
    @Results(id = "userMap",value = {
            @Result(id = true,column = "id",property = "id"),
            @Result(column = "username",property = "username"),
            @Result(column = "birthday",property = "birthday"),
            @Result(column = "sex",property = "sex"),
            @Result(column = "address",property = "address"),
            @Result(property = "accounts",column = "id",
                    many = @Many(select = "com.wedu.mybatis15.dao.IAccountDao.findAccountByUid",
                            fetchType = FetchType.LAZY))
    })
    List<User> findAll();

1.3、在IAccountDao接口中添加根据id查询方法


    /**
     * 根据用户id查询账户信息
     * @param id
     * @return
     */
    @Select("select * from account where uid=#{id}")
    Account findAccountByUid(Integer id);

1.3、在UserDaoTest的测试类中测试


    /**
     * 查询所有用户
     */
    @Test
    public void testFindAll() {
        List<User> users = userDao.findAll();
        for (User user : users) {
            System.out.println(user);
            System.out.println(user.getAccounts());
        }
    }

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