ssm-mybatis mapper补充之注解

注解说明

使用注解来映射简单语句会使代码显得更加简洁，但对于稍微复杂一点的语句，Java 注解不仅力不从心，还会让你本就复杂的 SQL 语句更加混乱不堪。
因此，如果你需要做一些很复杂的操作，最好用 XML 来映射语句，比如：嵌套联合映射。这里对一些简单的mapper用注解方式实现数据库操作。

准备工作

1. 工程配置

工程配置这里就不细说，可以看之前的入门操作说明：
https://blog.csdn.net/HenryChow_2015/article/details/119649897

2. 准备数据库表：新建班级、学生、班级学生映射表并写入一些测试数据

CREATE TABLE `class` (
  `id` int NOT NULL AUTO_INCREMENT COMMENT "班级id，主键，自增",
  `name` varchar(255) DEFAULT NULL COMMENT "班级名",
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;

CREATE TABLE `student` (
  `id` int NOT NULL AUTO_INCREMENT COMMENT "主键",
  `name` varchar(10) CHARACTER SET utf8 NOT NULL DEFAULT "123" COMMENT "姓名",
  `sex` varchar(10) CHARACTER SET utf8 DEFAULT NULL COMMENT "性别",
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=27 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;

CREATE TABLE `student_class_map` (
  `id` int NOT NULL AUTO_INCREMENT COMMENT "主键，自增",
  `student_id` int NOT NULL COMMENT "学生id",
  `class_id` int NOT NULL COMMENT "班级id",
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;

@Insert

1. mapper中编写插入接口，插入对象map都行

@Insert("INSERT INTO student (name, sex) VALUES(#{name}, #{sex})")
void insert(Student student);

2. 编写测试方法测试

@Test
public void insert() {
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
    Student student = new Student();
    student.setName("貂蝉");
    student.setSex("女");
    mapper.insert(student);
    sqlSession.close();
}

3. 运行查看结果

@Select

1. mapper中编写查询接口，返回到map list中

@Select("SELECT s.id as sid,s.`name` as sname,s.sex,c.id as cid,c.`name` as cname FROM student as s " +
        "LEFT JOIN student_class_map as sc ON s.id = sc.student_id " +
        "LEFT JOIN class as c ON sc.class_id = c.id WHERE s.sex = #{sex};")
List<Map<Object, Object>> getStudentAndClassListBySex(@Param("sex") String s);

2. 编写测试方法测试

@Test
public void getStudentAndClassListBySex() {
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
    for (Map map : mapper.getStudentAndClassListBySex("男")) {
        for (Object o : map.keySet()) {
            System.out.print(o + ":" + map.get(o) + " | ");
        }
        System.out.println();
    }
    sqlSession.close();
}

3. 运行查看结果

@Delete、@Update: 实现方式类似，不一一举例