本模块主要是对mybatis关联映射中一对一关联的添加和查询操作的整理，希望可以帮助到大家，建表和创建maven工程就不再赘述了~
1.1 一对一映射：添加
1.1.1 实体类：
Users类 |
Details类 |
package com.qhit.pojo;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.ToString;
@Data
@NoArgsConstructor
@AllArgsConstructor
@ToString
public class Users {
private int UserId;
private String UserName;
private String UserPwd;
private String UserRealName;
private String UserImg;
}
|
package com.qhit.pojo;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.ToString;
import org.omg.PortableInterceptor.INACTIVE;
@Data
@AllArgsConstructor
@NoArgsConstructor
@ToString
public class Details {
private int DetailId;
private String UserAddr;
private String UserTel;
private String UserDesc;
private int Uid;
}
|
1.1.2 mybatis主配置文件（mybatis-config.xml）：
配置mybatis-config.xml文件，使用properties标签引入外部文件来配置mysql连接信息，并注入UserMapper.xml文件以及DetailsMapper.xml文件;代码如下:
<?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"></properties>
<typeAliases>
<typeAlias type="com.qhit.pojo.Users" alias="Users"></typeAlias>
<typeAlias type="com.qhit.pojo.Details" alias="Details"></typeAlias>
</typeAliases>
<environments default="mysql">
<environment id="mysql">
<transactionManager type="JDBC"></transactionManager>
<dataSource type="POOLED">
<property name="driver" value="${mysql_driver}"/>
<property name="url" value="${mysql_url}"/>
<property name="username" value="${mysql_user}"/>
<property name="password" value="${mysql_password}"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="mappers/UserMapper.xml"></mapper>
<mapper resource="mappers/DetailsMapper.xml"></mapper>
</mappers>
</configuration>
1.1.3 SqlSession-工具类封装
封装SqlSession类，内置getSqlSession（boolean IsAutoCommit）设置是否自动提交（默认为false手动提交，true是自动提交）、getMapper（）方法;代码如下:
package com.qhit.Untils;
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 java.io.IOException;
import java.io.InputStream;
/**
* Description: NewSsm
* Created by WuHuaSen .
* Created Date: 2022/4/1 16:23
* Version: V1.0
*/
public class MybatisUtil {
//封装会话工厂
private static SqlSessionFactory Factory;
/**在进行对象的跨层传递的时候，使用ThreadLocal可以避免多次传递，打破层次间的约束
*/
private static ThreadLocal<SqlSession> local = new ThreadLocal<SqlSession>();
static {
try {
InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
Factory = sqlSessionFactoryBuilder.build(is);
} catch (
IOException e)
{
e.printStackTrace();
}
}
//封装factory方法
public static SqlSessionFactory getFactory(){
return Factory;
}
//封装sqlSession会话
public static SqlSession getSqlSession(boolean IsAutoComiit) {
SqlSession sqlSession = local.get();
if (sqlSession == null) {
sqlSession = Factory.openSession(IsAutoComiit);
local.set(sqlSession);
}
return sqlSession;
}
//使用泛型封装getMapper
public static <T extends Object> T getMapper(Class<T> c) {
SqlSession sqlSession = getSqlSession(true);
return sqlSession.getMapper(c);
}
}
1.1.4 接口层（Dao层）：
DAO接口层有两个UserDao接口、detailsDo接口，user表中有用户的基本的信息，details表中有用户的详细信息，同一个用户有一个基本信息和一个详信息，所以在做添加操作的时候不仅要添加User信息，也要添加Detail类信息吗，而且二者共同有一个Uid;代码如下:
|
UseDao接口 |
DetailsDao 接口 |
* Created Date: 2022/4/5 10:05
* Version: V1.0
*/
public interface UserDao {
//添加
public int InsertUser(Users users);
}
|
package com.qhit.Dao;
import com.qhit.pojo.Details;
import java.util.List;
public interface DetailsDao {
public int InsertDetail(Details details);
}
|
1.1.5 UserDao的映射文件：
UserDaomapper.xml中主要是对UserDao层中添加方法的实现，需要注意的是，在实现添加方法时，要对User_id进行回填，因为要根据User_id对Details进行数据添加，代码如下：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper 3.0" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.qhit.Dao.UserDao">
<sql id="User_column_list">
user_id,user_name,user_pwd,user_realname,user_img
</sql>
<resultMap id="UserMappers" type="Users">
<id column="user_id" property="UserId"></id>
<result column="user_name" property="UserName"></result>
<result column="user_pwd" property="UserPwd"></result>
<result column="user_realname" property="UserRealName"></result>
<result column="user_img" property="UserImg"></result>
</resultMap>
<!-- 添加-->
<insert id="InsertUser" useGeneratedKeys="true" keyProperty="UserId">
INSERT INTO users(user_id,user_name,user_pwd,user_realname,user_img)VALUES (#{UserId},#{UserName},#{UserPwd},#{UserRealName},#{UserImg})
</insert>
</mapper> 1.1.6 DetailDao的映射文件：
而DetailMapper.xml中则是对DetailDao层中的InsertDetail（）方法的实现，代码如下:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper 3.0" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.qhit.Dao.DetailsDao">
<resultMap id="DetalisMaper" type="Details">
<id column="detail_id" property="DetailId"></id>
<result column="user_addr" property="UserAddr"/>
<result column="user_tel" property="UserTel"/>
<result column="user_desc" property="UserDesc"/>
<result column="uid" property="Uid"/>
</resultMap>
<sql id="detail_column_list">
detail_id,user_addr,user_tel,user_desc,uid
</sql>
<insert id="InsertDetail">
INSERT INTO details (detail_id,user_addr,user_tel,user_desc,uid) VALUES (#{DetailId},#{UserAddr},#{UserTel},#{UserDesc},#{Uid})
</insert>
</mapper> 1.1.7 测试类
测试类中首先通过工具类获取到UserDao中的InsertUser(users user)方法对用户的基本信息进行添加，由于在UserMapper.xml文件中设置了主键回填，所以在添加完成后就可以获取到用户的id（user_id）也就是Details中的Uid，将user_id通过detail中的setUid(users.getUserId())赋值给Uid，然后在执行detailDao中的nsertDetail(Detail details)方法即可;
package com.qhit.Dao;
import com.qhit.Untils.MybatisUtil;
import com.qhit.pojo.Details;
import com.qhit.pojo.Users;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import java.util.List;
/**
* Description: mybatis002
* Created by WuHuaSen .
* Created Date: 2022/4/5 10:38
* Version: V1.0
*/
public class UserDaoTest {
MybatisUtil mybatisUtil = new MybatisUtil();
@Test
public void InsertUser() {
Users users = new Users(0, "wanger", "123456", "王二", "03.jpg",null);
Details details = new Details(0, "南通市", "1235333", "宁愿笑着流泪", 0);
// 用户注册，提交了基本信息和详情到servlet，servlet接收注册信息封装到User和details对象中
SqlSession sqlSession = mybatisUtil.getSqlSession(false);//手动提交
try {
UserDao userDao = sqlSession.getMapper(UserDao.class);
int i = userDao.InsertUser(users);
details.setUid(users.getUserId());
DetailsDao detailsDao = sqlSession.getMapper(DetailsDao.class);
int j = detailsDao.InsertDetail(details);
if (i == 1 && j == 1) {
sqlSession.commit();
System.out.println("-------添加成功！！！！------");
System.out.println(users);
System.out.println(details);
}
} catch (Exception e) {
System.out.println(e);
sqlSession.rollback();
}
}
}
需要注意的是，测试的时候调用MybatisUtil中的getSession（Boolean isAutoCommit）的时候需要传递一个false，或者调用MybatisUtil中getSession（）无参构造方法，设置为手动提交，因为要保证数据的一致性，即用户基本表和详情表同时添加成功才可以提交，否者回滚
2.1 一对一映射：查询（连接查询）
查询案例需求：根据用户的用户昵称（user_name）进行查询users表以及 details表中用户的详细信息。
2.1.1 实体类
在进行查询的时候，由于需要两张表的信息，为了能把两张表关联起来，需要对实体类User类新增一个属性即private Details detailsInfo，而Details类无需进行改变;以此即可建立起两张表的信息。代码如下；
Users类 |
Details类 |
package com.qhit.pojo;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.ToString;
@Data
@NoArgsConstructor
@AllArgsConstructor
@ToString
public class Users {
private int UserId;
private String UserName;
private String UserPwd;
private String UserRealName;
private String UserImg;
private Details detailsInfo;
} |
package com.qhit.pojo;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.ToString;
import org.omg.PortableInterceptor.INACTIVE;
@Data
@AllArgsConstructor
@NoArgsConstructor
@ToString
public class Details {
private int DetailId;
private String UserAddr;
private String UserTel;
private String UserDesc;
private int Uid;
}
|
2.1.2 接口层（Dao层）：
在userDao中定义一个public List<Users> queryUser(String UserName)方法，根据用户名查询用户的详细信息，而detailDao中在连接查询时无需操作即可，所以这里不需要在其定义方法。代码如下；
| UserDao 接口 |
package com.qhit.Dao;
import com.qhit.pojo.Users;
import java.util.List;
/**
* Description: mybatis002
* Created by WuHuaSen .
* Created Date: 2022/4/5 10:05
* Version: V1.0
*/
public interface UserDao {
//根据user_name查询
public List<Users> queryUser(String UserName);
}
|
2.1.3 UserDao的映射文件：
由于是查询操作所以需要指定映射关系，故需要建立ResultMap映射关系，而以往不同的时候，我们在此要做的是关联查询，在User实体类中添加了private Details detailsInfo，所以在建立对应关系的时候也需要对Details中的属性进行映射。代码如下：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper 3.0" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.qhit.Dao.UserDao">
<sql id="User_column_list">
user_id,user_name,user_pwd,user_realname,user_img
</sql>
<resultMap id="UserMappers" type="Users">
<id column="user_id" property="UserId"></id>
<result column="user_name" property="UserName"></result>
<result column="user_pwd" property="UserPwd"></result>
<result column="user_realname" property="UserRealName"></result>
<result column="user_img" property="UserImg"></result>
<result column="detail_id" property="detailsInfo.DetailId"></result>
<result column="user_addr" property="detailsInfo.UserAddr"></result>
<result column="user_tel" property="detailsInfo.UserTel"></result>
<result column="user_desc" property="detailsInfo.UserDesc"></result>
<!-- 根据 userName查询-->
<select id="queryUser" resultMap="UserMappers">
SELECT user_id,user_name,user_pwd,user_realname,user_img,detail_id,user_addr,user_tel,user_desc FROM users u INNER JOIN details d ON u.user_id=d.uid WHEREuser_name=#{UserName};
</select>
</mapper> 2.1.4 测试类
测试类直接通过工具类调用getSession（）来获取查询方法就可以；
package com.qhit.Dao;
import com.qhit.Untils.MybatisUtil;
import com.qhit.pojo.Details;
import com.qhit.pojo.Users;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import java.util.List;
/**
* Description: mybatis002
* Created by WuHuaSen .
* Created Date: 2022/4/5 10:38
* Version: V1.0
*/
public class UserDaoTest {
MybatisUtil mybatisUtil = new MybatisUtil();
//根据姓名查询
@Test
public void queryUser() {
UserDao userDao = mybatisUtil.getMapper(UserDao.class);
List<Users> users = userDao.queryUser("wanger");
System.out.println(users);
}
}
2.1.5 效果展示：
2.2 一对一映射：查询（子查询）
2.2.1 接口层（Dao）层
子查询的实体类与连接查询一致无需改动，主要是DetailsDao接口中添加了一个QueryDatailByUid方法以及mapper映射文件的改动。具体改动如下：
|
UseDao接口 |
DetailsDao 接口 |
* Created Date: 2022/4/5 10:05
* Version: V1.0
*/
public interface UserDao {
//根据userid查询
public List<Users> queryUser(String UserName);
}
|
package com.qhit.Dao;
import com.qhit.pojo.Details;
import java.util.List;
public interface DetailsDao {
public List<Details> QueryDatailByUid(int Uid);
}
|
2.2.2 UserDao的映射文件：
在UserDaomapper.xml相比关联查询，取消了部分映射关系的添加，而是使用accociation标签调用了子查询，关联查询一个对象，通过查询获取User_id,并通过accociation标签传递给com.qhit.Dao.DetailsDao.QueryDatailByUid（），而在UserDaomapper.xml中写SQL语句的时候只需要写查询User表即可；代码如下：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper 3.0" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.qhit.Dao.UserDao">
<sql id="User_column_list">
user_id,user_name,user_pwd,user_realname,user_img
</sql>
<resultMap id="UserMappers" type="Users">
<id column="user_id" property="UserId"></id>
<result column="user_name" property="UserName"></result>
<result column="user_pwd" property="UserPwd"></result>
<result column="user_realname" property="UserRealName"></result>
<result column="user_img" property="UserImg"></result>
<!-- accociation 调用了子查询，关联查询一个对象-->
<association property="detailsInfo" select="com.qhit.Dao.DetailsDao.QueryDatailByUid" column="user_id"/>
</resultMap>
<!-- 根据 userName查询-->
<select id="queryUser" resultMap="UserMappers">
SELECT user_id,user_name,user_pwd,user_realname,user_img FROM users WHERE user_name=#{UserName};
</select>
</mapper> 2.2.3 DetalisMaper的映射文件：
在DetalisMaper.xml主要是实现了Detalis接口中的QueryDatailByUid（）方法；代码如下：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper 3.0" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.qhit.Dao.DetailsDao">
<resultMap id="DetalisMaper" type="Details">
<id column="detail_id" property="DetailId"></id>
<result column="user_addr" property="UserAddr"/>
<result column="user_tel" property="UserTel"/>
<result column="user_desc" property="UserDesc"/>
<result column="uid" property="Uid"/>
</resultMap>
<sql id="detail_column_list">
detail_id,user_addr,user_tel,user_desc,uid
</sql>
<select id="QueryDatailByUid" resultMap="DetalisMaper">
SELECT
<include refid="detail_column_list"/>
FROM details WHERE uid=#{Uid};
</select>
</mapper> 2.2.4 Test测试类：
子查询的测试类与关联查询代码一致，无需任何更改，即可完成对数据的一对一的关联映射查询。代码如下：
package com.qhit.Dao;
import com.qhit.Untils.MybatisUtil;
import com.qhit.pojo.Details;
import com.qhit.pojo.Users;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import java.util.List;
/**
* Description: mybatis002
* Created by WuHuaSen .
* Created Date: 2022/4/5 10:38
* Version: V1.0
*/
public class UserDaoTest {
MybatisUtil mybatisUtil = new MybatisUtil();
//根据姓名查询
@Test
public void queryUser() {
UserDao userDao = mybatisUtil.getMapper(UserDao.class);
List<Users> users = userDao.queryUser("wanger");
System.out.println(users);
}
}
2.2.5 效果展示：
可以发现，无论是子查询还是连接查询，最后的结果都是一样的，相比之下连接查询更容易理解，但是书写的SQL语句较长；而子查询SQL语句较简单~
—–Thanks
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