mp项目快速预览

1. sql 文件

DROP TABLE IF EXISTS `user`;
 SET character_set_client = utf8mb4 ;
CREATE TABLE `user` (
  `id` int(11) NOT NULL  auto Increment,
  `name` varchar(45) DEFAULT NULL,
  `age` int(11) DEFAULT NULL,
  `create_time` timestamp NULL DEFAULT CURRENT_TIMESTAMP,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;

2. javaBean 文件

@Data
public class User {
    private long id;
    private String name;
    private int age;
    private LocalDateTime createTime;
}

3. mapper文件

public interface UserMapper extends BaseMapper<User> {
}

4. 测试

@RunWith(SpringRunner.class)
@SpringBootTest
public class SimpleTest {
    
    @Autowired
    private UserMapper userMapper;

    @Test
    public void select() {
        List<User>  users = userMapper.selectList(null);
        users.forEach(System.out::println);
    }
}

CRUD

1. BaseMapper
   我们通过使用command+7显示方法
   

   BaseMapper

2. 常用注解

• @TableName, 当数据库的表名(t_user)和bean中定义类名(User)不一致时候。@TableName("t_user")
• @TableField
  • 数据库的表名称(name)和bean中定义的名称(userName)不一致@TableField("name")
  • bean 中定义的某些字段(comment)不存在数据库中,用于其他用途。@TableField(exist=false)
• @TableId, 数据库中主键不是id比如为(user_id)时候,标注为数据库的主键。@TableId
  • bean中字段名称只能保持和数据库Id保持一致。如果想使用@TableField注解更改主键名，则会报错

@TableField("user_id")
@TableId
private long id;
//  会报异常,应该声明 为private long user_id

2. 插入数据

User user = new User();
user.setAge(33);
user.setName("yushui");
userMapper.insert(user);

3. 根据ID查询

• 查询单个实例selectById

public void selectById() {
        User user = userMapper.selectById(1L);
        System.out.println(user);
    }

sql语句

SELECT user_id,name AS realName,age,create_time FROM user WHERE user_id=?

• 查询多个实例selectBatchIds

    public void selectBatch() {
        List<Long> list = Arrays.asList(1L, 2L);
        List<User>  users =  userMapper.selectBatchIds(list);
        users.forEach(System.out::println);
    }

sql 语句

SELECT user_id,name AS realName,age,create_time FROM user WHERE user_id IN ( ? , ? )

• where 条件查询

Map<String, Object> columnMap = new HashMap<>();
columnMap.put("name", "y1shui");
columnMap.put("age", "33");
List<User> users = userMapper.selectByMap(columnMap);
users.forEach(System.out::println);

sql 语句

SELECT user_id,name AS realName,age,create_time FROM user WHERE name = ? AND age = ?