1 <dependencies>
2     <!-- https://mvnrepository.com/artifact/org.projectlombok/lombok -->
3     <dependency>
4         <groupId>org.projectlombok</groupId>
5         <artifactId>lombok</artifactId>
6         <version>1.18.10</version>
7     </dependency>
8 </dependencies>

 1 @Getter and @Setter
 2 @FieldNameConstants
 3 @ToString
 4 @EqualsAndHashCode
 5 @AllArgsConstructor, @RequiredArgsConstructor and @NoArgsConstructor
 6 @Log, @Log4j, @Log4j2, @Slf4j, @XSlf4j, @CommonsLog, @JBossLog, @Flogger, @CustomLog
 7 @Data
 8 @Builder
 9 @SuperBuilder
10 @Singular
11 @Delegate
12 @Value
13 @Accessors
14 @Wither
15 @With
16 @SneakyThrows
17 @val
18 @var
19 experimental @var
20 @UtilityClass
21 Lombok config system
22 Code inspections
23 Refactoring actions (lombok and delombok)

 1 import lombok.Data;
 2 
 3 //实体类
 4 @Data
 5 public class User {
 6     private int id;  //id
 7     private String name;   //姓名
 8     private String password;   //密码
 9 
10 
11 }

 1 CREATE TABLE `teacher` (
 2   `id` INT(10) NOT NULL,
 3   `name` VARCHAR(30) DEFAULT NULL,
 4   PRIMARY KEY (`id`)
 5 ) ENGINE=INNODB DEFAULT CHARSET=utf8;
 6 
 7 INSERT INTO teacher(`id`, `name`) VALUES (1, ‘秦老师‘); 
 8 
 9 CREATE TABLE `student` (
10   `id` INT(10) NOT NULL,
11   `name` VARCHAR(30) DEFAULT NULL,
12   `tid` INT(10) DEFAULT NULL,
13   PRIMARY KEY (`id`),
14   KEY `fktid` (`tid`),
15   CONSTRAINT `fktid` FOREIGN KEY (`tid`) REFERENCES `teacher` (`id`)
16 ) ENGINE=INNODB DEFAULT CHARSET=utf8;
17 
18 
19 INSERT INTO `student` (`id`, `name`, `tid`) VALUES (‘1‘, ‘小明‘, ‘1‘); 
20 INSERT INTO `student` (`id`, `name`, `tid`) VALUES (‘2‘, ‘小红‘, ‘1‘); 
21 INSERT INTO `student` (`id`, `name`, `tid`) VALUES (‘3‘, ‘小张‘, ‘1‘); 
22 INSERT INTO `student` (`id`, `name`, `tid`) VALUES (‘4‘, ‘小李‘, ‘1‘); 
23 INSERT INTO `student` (`id`, `name`, `tid`) VALUES (‘5‘, ‘小王‘, ‘1‘); 

 1 import lombok.Data;
 2 
 3 @Data
 4 public class Student {
 5 
 6     private int id;
 7     private String name;
 8 
 9     //学生需要关联一个老师
10     private Teacher teacher;
11 }

1 import lombok.Data;
2 
3 @Data
4 public class Teacher {
5 
6     private int id;
7     private String name;
8 }

1 select s.id as ‘学生id‘,s.name as ‘学生姓名‘,t.id as ‘老师id‘,t.name as ‘老师姓名‘ from student s ,teacher t where s.tid = t.id;

1 List<Student> getStudent();

 1 <!--需要查询所有学生信息以及对应的老师信息-->
 2 <resultMap id="StudentTeacher" type="Student">
 3     <result property="id" column="id"></result>
 4     <result property="name" column="name"></result>
 5 
 6     <!--复杂的属性，我们需要单独处理， 对象使用association，集合使用collection-->
 7     <!--property属性名 javaType属性类型 column表中的列名-->
 8     <association property="teacher" column="tid" javaType="Teacher" select="getTeacher"></association>
 9 </resultMap>
10 
11 <select id="getStudent" resultMap="StudentTeacher">
12     select * from mybatis.student;
13 </select>
14 
15 <select id="getTeacher" parameterType="_int" resultType="Teacher">
16     select * from mybatis.teacher where id=#{teacherId};
17 </select>

 1 @Test
 2 public void getStudentTest() {
 3     SqlSession session = MybatisUtils.getSession();
 4 
 5     StudentMapper mapper = session.getMapper(StudentMapper.class);
 6 
 7     List<Student> studentList = mapper.getStudent();
 8 
 9     for (Student student : studentList) {
10         System.out.println(student);
11     }
12 
13     session.close();
14 }

1 List<Student> getStudent2();

 1 <!--方式二：连表查询-->
 2 <select id="getStudent2" resultMap="StudentTeacher2">
 3     select s.id as sid,s.name as sname,t.id as tid,t.name as tname
 4     from student s ,teacher t
 5     where s.tid = t.id;
 6 </select>
 7 
 8 <resultMap id="StudentTeacher2" type="Student">
 9     <result property="id" column="sid"></result>
10     <result property="name" column="sname"></result>
11     <association property="teacher" javaType="Teacher">
12         <result property="id" column="tid"></result>
13         <result property="name" column="tname"></result>
14     </association>
15 </resultMap>

 1 @Test
 2 public void getStudent2Test() {
 3     SqlSession session = MybatisUtils.getSession();
 4 
 5     StudentMapper mapper = session.getMapper(StudentMapper.class);
 6 
 7     List<Student> studentList = mapper.getStudent2();
 8 
 9     for (Student student : studentList) {
10         System.out.println(student);
11     }
12 
13     session.close();
14 }

1 import lombok.Data;
2 
3 @Data
4 public class Student {
5 
6     private int id;
7     private String name;
8     private int tid;
9 }

 1 import lombok.Data;
 2 
 3 import java.util.List;
 4 
 5 @Data
 6 public class Teacher {
 7 
 8     private int id;
 9     private String name;
10 
11     //一个老师拥有多个学生
12     private List<Student> students;
13 }

1 select t.id as tid, t.name as tname,s.id as sid, s.name as sname
2 from student s,teacher t
3 where s.tid = t.id;

1 Teacher getTeacher2(@Param("tid") int id);

 1 <select id="getTeacher2" resultMap="TeacherStudent2">
 2     select id , name from mybatis.teacher where id = #{tid}
 3 </select>
 4 
 5 <resultMap id="TeacherStudent2" type="Teacher">
 6     <result property="id" column="id"></result>
 7     <result property="name" column="name"></result>
 8     <collection property="students" javaType="ArrayList" ofType="Student" select="getStudentByTeacherId" column="id"></collection>
 9 </resultMap>
10 
11 <select id="getStudentByTeacherId" resultType="Student">
12     select * from mybatis.student where tid = #{tid};
13 </select>

 1 @Test
 2 public void getTeacherTest2() {
 3     SqlSession session = MybatisUtils.getSession();
 4 
 5     TeacherMapper mapper = session.getMapper(TeacherMapper.class);
 6 
 7     Teacher teacher = mapper.getTeacher2(1);
 8 
 9     System.out.println(teacher);
10 
11     session.close();
12 }

1 //根据老师id获得老师信息并获得对应的多个学生信息
2 Teacher getTeacher(@Param("tid") int id);

 1 <!--联表查询方式-->
 2     <select id="getTeacher" resultMap="TeacherStudent">
 3         select t.id as tid, t.name as tname,s.id as sid, s.name as sname
 4         from student s,teacher t
 5         where s.tid = t.id and t.id = #{tid};
 6     </select>
 7 
 8     <resultMap id="TeacherStudent" type="Teacher">
 9         <result property="id" column="tid"></result>
10         <result property="name" column="tname"></result>
11         <!--集合的话，使用collection！
12                 JavaType和ofType都是用来指定对象类型的
13                 JavaType是用来指定pojo中属性的类型
14                 ofType指定的是映射到list集合属性中pojo的类型。-->
15         <collection property="students" ofType="Student">
16             <result property="id" column="sid"></result>
17             <result property="name" column="sname"></result>
18             <result property="tid" column="tid"></result>
19         </collection>
20     </resultMap>

 1 @Test
 2 public void getTeacherTest() {
 3     SqlSession session = MybatisUtils.getSession();
 4 
 5     TeacherMapper mapper = session.getMapper(TeacherMapper.class);
 6 
 7     Teacher teacher = mapper.getTeacher(1);
 8 
 9     System.out.println(teacher);
10 
11     session.close();
12 }