用mybatis-plus-join写一个迷糊查询

首先，需要在pom.xml中添加mybatis-plus和数据库驱动的依赖：

<dependencies>
    <!-- mybatis-plus -->
    <dependency>
        <groupId>com.baomidou</groupId>
        <artifactId>mybatis-plus-boot-starter</artifactId>
        <version>3.4.2</version>
    </dependency>
    <!-- 数据库驱动 -->
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>8.0.26</version>
    </dependency>
</dependencies>

接着，创建实体类和mapper接口，以User和Order为例：

User实体类：

@Data
public class User {
    private Long id;
    private String name;
    private Integer age;
}

UserMapper接口：

@Mapper
public interface UserMapper extends BaseMapper<User> {
}

Order实体类：

@Data
public class Order {
    private Long id;
    private Long userId;
    private String orderNo;
    private Date createTime;
}

OrderMapper接口：

@Mapper
public interface OrderMapper extends BaseMapper<Order> {
}

然后，在UserService中使用mybatis-plus-join实现迷糊查询：

@Service
public class UserService {
    @Autowired
    private UserMapper userMapper;
    @Autowired
    private OrderMapper orderMapper;

    public List<User> findUsersByNameLike(String name) {
        QueryWrapper<User> userWrapper = new QueryWrapper<>();
        userWrapper.like("name", name);
        return userMapper.selectList(userWrapper);
    }

    public List<User> findUsersByOrderCreateTimeBetween(Date start, Date end) {
        QueryWrapper<User> userWrapper = new QueryWrapper<>();
        userWrapper.inSql("id", "select user_id from `order` where create_time between #{start} and #{end}");
        return userMapper.selectList(userWrapper);
    }

    public List<User> findUsersByOrderNoLike(String orderNo) {
        QueryWrapper<User> userWrapper = new QueryWrapper<>();
        userWrapper.inSql("id", "select user_id from `order` where order_no like concat('%', #{orderNo}, '%')");
        return userMapper.selectList(userWrapper);
    }

    public List<User> findUsersByOrderNoLikeAndAgeBetween(String orderNo, Integer startAge, Integer endAge) {
        QueryWrapper<User> userWrapper = new QueryWrapper<>();
        userWrapper.inSql("id", "select user_id from `order` where order_no like concat('%', #{orderNo}, '%')")
                .between("age", startAge, endAge);
        return userMapper.selectList(userWrapper);
    }
}

其中，findUsersByNameLike方法实现了根据用户姓名模糊查询的功能；findUsersByOrderCreateTimeBetween方法实现了查询在某个时间范围内下单的用户列表；findUsersByOrderNoLike方法实现了根据订单号模糊查询的功能；findUsersByOrderNoLikeAndAgeBetween方法实现了根据订单号模糊查询，并且年龄在某个范围内的用户列表。