MyBatis关联查询：一对一

数据表

项目框架搭建 第一步：创建Maven项目

• 添加Maven依赖：

        junit
        junit
        4.12
        test
    

    
        log4j
        log4j
        1.2.17
    

    
        org.projectlombok
        lombok
        1.18.10
    

    
        mysql
        mysql-connector-java
        8.0.18
    
    
        org.mybatis
        mybatis
        3.5.4
    

• 指定Mapper XML文件在mybatis-config.xml中的配置有效，强制部署resources目录到classes

    
        src/main/resources
        
            **/*.xml
        
    
    
        ${basedir}/src/main/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：工具类MyBatisUtil

public class MyBatisUtil {
    private static String CONFIG_FILE_LOCATION = "mybatis-config.xml";
    private static final ThreadLocal threadLocal = new ThreadLocal();
    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);
        }
    }
}

第四步：实体类

• Idcard

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

    private static final long serialVersionUID = -8256986024750029520L;

    private Integer id;  //封装数据类型
    private String num;
    private String nation;
}

• Person

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

    private static final long serialVersionUID = 3252228568741916300L;

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

    /
    private  Idcard idcard;
}

XML方式 第一步：创建mybatis-config.xml

DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">

    
    

    
        
    

    
        
            
        
    

    
        
            
              
                
                
                
                
            
        
    

    
        
    

注意：mappers标签中使用的是resouce

第二步：PersonDao

public interface PersonDao {
      Person selectPersonWithIdcardByName(String name);
}

第三步：PersonMapper.xml

    
        
        
        
        
        
            
            
            
        
    

    
        select * from tb_person
        inner join tb_idcard
        on tb_person.id = tb_idcard.id
        where  tb_person.name = #{name}
    

测试代码

public class PersonDaoTest {

    @Test
    public void getPersonWithIdcardByName() {
        SqlSession session = MyBatisUtil.getSession();
        PersonDao personDao= session.getMapper(PersonDao.class);
        Person person = personDao.selectPersonWithIdcardByName("lisi");
        System.out.println(person);
        System.out.println(person.getIdcard());
    }

}

注解方式 第一步：创建mybatis-config.xml

DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">


    
    

    
        
        
    

    
        
            
              
                
                
                
                
            
        
    
    
    
        
        
    

注意：mapper标签中使用的是class

第二步：创建Dao接口

• IdcardDao

public interface IdcardDao {
    @Select("select * from tb_idcard")
    Idcard selectIdcardById(Integer id);
}

• PersonDao

public interface PersonDao{
      @Select("SELECT * FROM tb_person where name= #{name}")
      @Results({
              @Result(id=true,column="id",property="id"),
              @Result(column="name",property="name"),
              @Result(column="gender",property="gender"),
              @Result(column="birth",property="birth"),
              @Result(
                      column="card_id",property="idcard",
                      one=@One( select="com.hc.one2one.dao.IdcardDao.selectIdcardById", fetchType= FetchType.EAGER )
              )
      })
      Person selectPersonWithIdcardByName(String name);
}

测试代码

public class PersonDaoTest {

    @Test
    public void getPersonWithIdcardByName() {
        SqlSession session = MyBatisUtil.getSession();
        PersonDao personDao= session.getMapper(PersonDao.class);
        Person person = personDao.selectPersonWithIdcardByName("lisi");
        System.out.println(person);
        System.out.println(person.getIdcard());
    }

}