Mybatis 一对 多对 按结果嵌套处理

实体类

  @Data
  public class Student { -- 学生
      private int id;
      private String name;
      private int tid;
  }    

  @Data
  public class Teacher {-- 老师
        private int id;
        private String name;
        private List<Student> students;
  }

新建学生mapper接口

  public interface TeacherMapper{
      //获取指定老师下的所有学生及老师的信息
      Teacher getTeacherById(@Param("tid")int id);
  }

按结果嵌套处理

在resources 下新建mapper.xml

  <?xml version="1.0" encoding="UTF-8" ?>
  <!DOCTYPE mapper
          PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
          "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  <mapper namespace="com.rzk.mapper.TeacherMapper">
      <!--按结果嵌套查询-->
      <select id="getTeacherById" resultMap="getStudent">
          SELECT s.id sid,s.name sname,t.name tname,t.id tid
          from student s, teacher t
          where s.tid = t.id and t.id = #{tid}
      </select>

      <resultMap id="getStudent" type="Teacher">
          <result property="id" column="tid"/>
          <result property="name" column="tname"/>
          <!--
              复杂的属性,我们需要单独处理  对象: association  集合: collection
              javaType="" 指定属性的类型!
              集合中的泛型信息,我们使用ofType获取
          -->
          <collection property="students" ofType="Student">
              <result property="id" column="sid"/>
              <result property="name" column="sname"/>
              <result property="tid" column="tid"/>
          </collection>
      </resultMap>
  </mapper>

db.propers

  driver=com.mysql.jdbc.Driver
  url=jdbc:mysql://localhost:3306/mybatis?useUnicode=true&characterEncoding=UTF-8
  username=root      
  password=123456

logger

  log4j.rootLogger=DEBUG,console,file

  #控制台输出的相关设置
  log4j.appender.console = org.apache.log4j.ConsoleAppender
  log4j.appender.console.Target = System.out
  log4j.appender.console.Threshold=DEBUG
  log4j.appender.console.layout = org.apache.log4j.PatternLayout
  #log4j.appender.console.layout.ConversionPattern=[%c]-%m%n
  log4j.appender.console.layout.ConversionPattern=%5p [%t] - %m%n

  #文件输出的相关设置
  log4j.appender.file = org.apache.log4j.RollingFileAppender
  log4j.appender.file.File=./log/rzk.log
  log4j.appender.file.MaxFileSize=10mb
  log4j.appender.file.Threshold=DEBUG
  log4j.appender.file.layout=org.apache.log4j.PatternLayout
  log4j.appender.file.layout.ConversionPattern=[%p][%d{yy-MM-dd}][%c]%m%n

  #日志输出级别
  log4j.logger.org.mybatis=DEBUG
  log4j.logger.java.sql=DEBUG
  log4j.logger.java.sql.Statement=DEBUG
  log4j.logger.java.sql.ResultSet=DEBUG
  log4j.logger.java.sql.PreparedStatement=DEBUG

mybatis-config.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">
  <!--configguration核心配置文件-->
  <configuration>


      <!--导入外部配置文件-->
      <properties resource="db.properties"/>
      <!--标准日志工厂实现-->
      <!--   <settings>
             <setting name="logImpl" value="STDOUT_LOGGING"/>
         </settings>-->
      <settings>
          <setting name="logImpl" value="LOG4J"/>
      </settings>
      <!--给实体类起别名-->
      <typeAliases>
          <package name="com.rzk.pojo" />
      </typeAliases>
      <environments default="development">
          <environment id="development">
              <transactionManager type="JDBC"/>
              <dataSource type="POOLED">
                  <property name="driver" value="${driver}"/>
                  <property name="url" value="${url}"/>
                  <property name="username" value="${username}"/>
                  <property name="password" value="${password}"/>
              </dataSource>
          </environment>
      </environments>
      <mappers>
          <mapper resource="com/rzk/mapper/StudentMapper.xml"/>
          <mapper resource="com/rzk/mapper/TeacherMapper.xml"/>
      </mappers>
  </configuration>

测试结果

总结

1.关联 - association [多对一]
2.集合 - collection [一对多]
3.javaType & ofType
1.javaType用来指定实体类中属性的类型
2.ofType 用来指定映射到List或者集合中的pojo类型,泛型中约束类型