1.搭建数据库环境
CREATE TABLE `teacher`(
`id` INT(10) NOT NULL,
`name` VARCHAR(30) DEFAULT NULL,
PRIMARY KEY (`id`)
)ENGINE=INNODB DEFAULT CHARSET=utf8
INSERT INTO teacher(`id`,`name`)VALUES(1,'张老师');
CREATE TABLE `student`(
`id` INT(10) NOT NULL,
`name` VARCHAR (30) DEFAULT NULL,
`tid` INT(10) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `fktid`(`tid`),
CONSTRAINT `fktid` FOREIGN KEY(`tid`) REFERENCES `teacher` (`id`)
)ENGINE=INNODB DEFAULT CHARSET=utf8
INSERT INTO `student`(`id`,`name`,`tid`)VALUES(1,'小沈',1);
INSERT INTO `student`(`id`,`name`,`tid`)VALUES(2,'小张',1);
INSERT INTO `student`(`id`,`name`,`tid`)VALUES(3,'小牛',1);
INSERT INTO `student`(`id`,`name`,`tid`)VALUES(4,'小白',1);
INSERT INTO `student`(`id`,`name`,`tid`)VALUES(5,'小黑',1);
2.实体类
@Data
public class Student {
private int id;
private String name;
private int tid;
}
@Data
public class Teacher {
private int id;
private String name;
//一个老师拥有多个学生
private List<Student> students;
}
按照结果嵌套处理
连表查询
public interface TeacherMapper {
public List<Teacher> getTeacher(@Param("id") int id);
}
用resultMap,不用resultType是因为查询老师操作中学生对象会为空,数据库中的值与java中的实体类没有对应上, javaType是指定属性的返回值类型,ofType是指定属性中的泛型
<select id="getTeacher" resultMap="getStudent">
select t.name tn,s.id sid,s.name sn from mybatis.teacher t,mybatis.student s where t.id=s.tid and t.id=#{id};
</select>
<resultMap id="getStudent" type="Teacher">
<result property="name" column="tn"/>
<collection property="students" ofType="Student">
<result property="id" column="sid"/>
<result property="name" column="tn"/>
</collection>
</resultMap>
按照查询嵌套处理
public List<Teacher> getTeacher1(@Param("id") int id);
<select id="getTeacher1" resultMap="getStudent1">
select t.name tn from mybatis.teacher t where id=#{id};
</select>
<resultMap id="getStudent1" type="Teacher">
<result property="name" column="tn"/>
<collection property="students" javaType="ArrayList" ofType="Student" select="getStuByTeaId" column="id"/>
</resultMap>
<select id="getStuByTeaId" resultType="Student">
select *from mybatis.student;
</select>