入门使用mybatis-plus

第一步：pom文件带入依赖

<dependency><groupId>com.baomidou</groupId><artifactId>mybatis-plus-boot-starter</artifactId><version>3.5.1</version>
</dependency>

 第二步：创建实体对象

@TableName("leave_request")
@Data
@AllArgsConstructor
@NoArgsConstructor
public class LeaveRequest {@TableIdprivate int id;private String requestUuid;private String title;private Integer leaveDay;private LocalDate leaveStartTime;private LocalDate leaveEndTime;private String requestorName;private String teamLeader;private String sourcingManager;private String DbsBoss;private String NCSTeamLeader;private String status;}

 需要注意的是@TableName("leave_request")，这个东西对应你数据库里面的表

 

第三步：@Mapper和@MapperScan必须二选一

@SpringBootApplication(exclude= SecurityAutoConfiguration.class)
@MapperScan("com.example.demo.Mappers")
public class DemoApplication {public static void main(String[] args) {SpringApplication.run(DemoApplication.class, args);}}

@MapperScan("com.example.demo.Mappers")里面的value对应你第四步的文件路径

 

  第四步：创建实体类对应的repository，增删查改的语句就可以在这里面进行填写

@Repository
public interface LeaveRequestMapper extends BaseMapper<LeaveRequest> {LeaveRequest findByRequestUuid(String requestUuid);}

可以通过命名的方式不用写sql语句即可实现查询。下面是基本的查询方式：

/**
 * 普通查询
 */
@Test
public void selectById() {
    UserInfo userInfo = userInfoMapper.selectById(123);
    System.out.println(userInfo);
}
 
/**
 * 批量查询
 */
@Test
public void selectByIds() {
    List<Long> ids = Arrays.asList(123L,124L,125L);
    List<UserInfo> userInfo = userInfoMapper.selectBatchIds(ids);
    System.out.println(userInfo);
}
 
/**
 * 名字包含娟并且年龄小于30
 */
@Test
public void selectByWrapper() {
    QueryWrapper<UserInfo> queryWrapper = new QueryWrapper<UserInfo>();
    queryWrapper.like("username","娟").lt("age",30);
    List<UserInfo> userInfoList = userInfoMapper.selectList(queryWrapper);
    userInfoList.forEach(System.out::println);
}
/**
 * 名字包含娟并且年龄大于等于20且小于等于40并且email不为空
 */
@Test
public void selectByWrapper2() {
    QueryWrapper<UserInfo> queryWrapper = new QueryWrapper<UserInfo>();
    queryWrapper.like("username","娟").between("age",20,30).isNotNull("email");
    List<UserInfo> userInfoList = userInfoMapper.selectList(queryWrapper);
    userInfoList.forEach(System.out::println);
}
 
/**
 * 名字姓肖或者年量大于等于20，按照年龄降序排列，年龄相同按照id生序排列
 */
@Test
public void selectByWrapper3() {
    QueryWrapper<UserInfo> queryWrapper = new QueryWrapper<UserInfo>();
    queryWrapper.likeRight("username","肖")
            .or().ge("age",20).orderByDesc("age").orderByAsc("id");
    List<UserInfo> userInfoList = userInfoMapper.selectList(queryWrapper);
    userInfoList.forEach(System.out::println);
}
 
/**
 * 创建日期为2024年1月2日并且直属上级名字为王姓
 */
@Test
public void selectByWrapper4() {
    QueryWrapper<UserInfo> queryWrapper = new QueryWrapper<UserInfo>();
    queryWrapper.apply("date_format(create_time,'%Y-%m-%d')={0}","2024-10-02")
            .inSql("parent_id","select id from user where username like '王%'");
    List<UserInfo> userInfoList = userInfoMapper.selectList(queryWrapper);
    userInfoList.forEach(System.out::println);
}
 
//上面的日期查询使用的是占位符的形式进行查询，目的就是为了防止SQL注入的风险
 
/**
 * 名字为王姓并且（年龄小于40或邮箱不为空）
 */
@Test
public void selectByWrapper5() {
    QueryWrapper<UserInfo> queryWrapper = new QueryWrapper<UserInfo>();
    queryWrapper.likeRight("username","王")
            .and(wq->wq.lt("age",40))
            .or().isNotNull("email");
    List<UserInfo> userInfoList = userInfoMapper.selectList(queryWrapper);
    userInfoList.forEach(System.out::println);
}
/**
 * 名字为王姓并且（年龄小于40并且大与20或邮箱不为空）
 */
@Test
public void selectByWrapper6() {
    QueryWrapper<UserInfo> queryWrapper = new QueryWrapper<UserInfo>();
    queryWrapper.likeRight("username","王")
            .and(wq->wq.lt("age",40).gt("age",20))
            .or().isNotNull("email");
    List<UserInfo> userInfoList = userInfoMapper.selectList(queryWrapper);
    userInfoList.forEach(System.out::println);
}
/**
 * （年龄小于40并且大与20或邮箱不为空）并且名字为王姓
 */
@Test
public void selectByWrapper7() {
    QueryWrapper<UserInfo> queryWrapper = new QueryWrapper<UserInfo>();
    queryWrapper.nested(wq->wq.lt("age",40).gt("age",20))
            .or().isNotNull("email")
            .likeRight("username","王");
    List<UserInfo> userInfoList = userInfoMapper.selectList(queryWrapper);
    userInfoList.forEach(System.out::println);
}
/**
 * 年龄23，30，40
 */
@Test
public void selectByWrapper8() {
    QueryWrapper<UserInfo> queryWrapper = new QueryWrapper<UserInfo>();
    queryWrapper.in("age",Arrays.asList(20,30,40));
    List<UserInfo> userInfoList = userInfoMapper.selectList(queryWrapper);
    userInfoList.forEach(System.out::println);
}
/**
 * 只返回满足条件的其中一条语句即可
 */
@Test
public void selectByWrapper9() {
    QueryWrapper<UserInfo> queryWrapper = new QueryWrapper<UserInfo>();
    queryWrapper.in("age",Arrays.asList(20,30,40)).last("limit 1");
    List<UserInfo> userInfoList = userInfoMapper.selectList(queryWrapper);
    userInfoList.forEach(System.out::println);
}
 
/**
 * 名字中包含雨并且年龄小于40(只取id,username)
 */
@Test
public void selectByWrapper10() {
    QueryWrapper<UserInfo> queryWrapper = new QueryWrapper<UserInfo>();
    queryWrapper.select("id","username").like("username","雨").lt("age",40);
    List<UserInfo> userInfoList = userInfoMapper.selectList(queryWrapper);
    userInfoList.forEach(System.out::println);
}
 
/**
 * 名字中包含雨并且年龄小于40(不取create_time,parent_id两个字段,即不列出全部字段)
 */
@Test
public void selectByWrapper11() {
    QueryWrapper<UserInfo> queryWrapper = new QueryWrapper<UserInfo>();
    queryWrapper.like("username","雨").lt("age",40)
                .select(UserInfo.class,info->!info.getColumn().equals("create_time")&&
                        !info.getColumn().equals("parent_id"));
    List<UserInfo> userInfoList = userInfoMapper.selectList(queryWrapper);
    userInfoList.forEach(System.out::println);
}
 
/**
 * 姓名和邮箱不为空
 */
public void testCondition() {
    String username = "王";
    String email = "";
    condition(username,email);
}
 
private void condition(String username,String email){
    QueryWrapper<UserInfo> queryWrapper = new QueryWrapper<UserInfo>();
    queryWrapper.like(StringUtils.isNullOrEmpty(username),"name",username)
                .like(StringUtils.isNullOrEmpty(email),"email",email);
    List<UserInfo> userInfoList = userInfoMapper.selectList(queryWrapper);
    userInfoList.forEach(System.out::println);
}
 
/**
 * 实体作为条件构造器方法的参数
 */
@Test
public void selectByWrapperEntity() {
    UserInfo whereUser = new UserInfo();
    whereUser.setUsername("xiaojuan");
    whereUser.setAge(22);
    QueryWrapper<UserInfo> queryWrapper = new QueryWrapper<UserInfo>(whereUser);
    List<UserInfo> userInfoList = userInfoMapper.selectList(queryWrapper);
    userInfoList.forEach(System.out::println);
}
/**
 * AllEq用法
 */
@Test
public void selectByWrapperAllEq() {
    QueryWrapper<UserInfo> queryWrapper = new QueryWrapper<UserInfo>();
    Map<String, Object> params = new HashMap<String, Object>();
    params.put("nuserame","xiaojuan");
    params.put("age",null);
    queryWrapper.allEq(params);
    List<UserInfo> userInfoList = userInfoMapper.selectList(queryWrapper);
    userInfoList.forEach(System.out::println);
}
 
/**
 * AllEq用法(排除不是条件的字段)
 */
@Test
public void selectByWrapperAllEq2() {
    QueryWrapper<UserInfo> queryWrapper = new QueryWrapper<UserInfo>();
    Map<String, Object> params = new HashMap<String, Object>();
    params.put("nuserame","xiaojuan");
    params.put("age",null);
    queryWrapper.allEq((k,v)->!k.equals("name"),params);
    List<UserInfo> userInfoList = userInfoMapper.selectList(queryWrapper);
    userInfoList.forEach(System.out::println);
}
 
/**
 * selectMaps
 */
@Test
public void selectByWrapperMaps() {
    QueryWrapper<UserInfo> queryWrapper = new QueryWrapper<UserInfo>();
    queryWrapper.like("name","肖").lt("age",40);
    List<Map<String,Object>> userInfoList = userInfoMapper.selectMaps(queryWrapper);
    userInfoList.forEach(System.out::println);
}
 
/**
 * 按照直属上级分组，查询每组的平均年龄，最大年龄，最小年龄。并且只取年龄总和小于500的组
 */
@Test
public void selectByWrapperMaps2() {
    QueryWrapper<UserInfo> queryWrapper = new QueryWrapper<UserInfo>();
    queryWrapper.select("avg(age) avg_age","min(min) min_age","max(age) max_age")
            .groupBy("parent_id").having("sum(age)<{0}",500);
    List<Map<String,Object>> userInfoList = userInfoMapper.selectMaps(queryWrapper);
    userInfoList.forEach(System.out::println);
}
 
/**
 * selectObjs
 */
@Test
public void selectByWrapperObjs() {
    QueryWrapper<UserInfo> queryWrapper = new QueryWrapper<UserInfo>();
    queryWrapper.select("id","name").like("name","肖").lt("age",40);
    List<Object> userInfoList = userInfoMapper.selectObjs(queryWrapper);
    userInfoList.forEach(System.out::println);
}
 
/**
 * selectCount
 */
@Test
public void selectByWrapperCount() {
    QueryWrapper<UserInfo> queryWrapper = new QueryWrapper<UserInfo>();
    queryWrapper.like("name","肖").lt("age",40);
    Integer count = userInfoMapper.selectCount(queryWrapper);
    System.out.println(count);
}
 
/**
 * selectOne
 */
@Test
public void selectByWrapperSelectOne() {
    QueryWrapper<UserInfo> queryWrapper = new QueryWrapper<UserInfo>();
    queryWrapper.like("name","肖").lt("age",40);
    UserInfo user = userInfoMapper.selectOne(queryWrapper);
    System.out.println(user);
}
 
/**
 * 使用Lambda
 */
@Test
public void selectLambda() {
   // LambdaQueryWrapper<UserInfo> lambda = new QueryWrapper<UserInfo>().lambda();
    LambdaQueryWrapper<UserInfo> lambda = new LambdaQueryWrapper<UserInfo>();
    lambda.like(UserInfo::getUsername,"娟").lt(UserInfo::getAge,40);
    List<UserInfo> userInfoList = userInfoMapper.selectList(lambda);
    userInfoList.forEach(System.out::println);
}
 
/**
 * 使用Lambda,名字为王姓（年龄小于40或邮箱不为空）
 */
@Test
public void selectLambd2() {
    LambdaQueryWrapper<UserInfo> lambda = new LambdaQueryWrapper<UserInfo>();
    lambda.like(UserInfo::getUsername,"娟")
            .and(lqw->lqw.lt(UserInfo::getAge,40).or().isNotNull(UserInfo::getEmail));
    List<UserInfo> userInfoList = userInfoMapper.selectList(lambda);
    userInfoList.forEach(System.out::println);
}
 
/**
 * 使用Lambda链式
 */
@Test
public void selectLambd3() {
    List<UserInfo> userInfoList = new LambdaQueryChainWrapper<UserInfo>(userInfoMapper)
            .like(UserInfo::getUsername,"娟").ge(UserInfo::getAge,20).list();
    userInfoList.forEach(System.out::println);