Question

我有这 3 个独立的表，即学生、教师和主题。这里的独立是指这些表之间没有关系。

我想要所有这些表的数量。 SQL 查询看起来像 -

import numpy as np
import cv2 as cv
from sklearn.cluster import MeanShift, estimate_bandwidth


img = cv.imread(your_image)

# filter to reduce noise
img = cv.medianBlur(img, 3)

# flatten the image
flat_image = img.reshape((-1,3))
flat_image = np.float32(flat_image)

# meanshift
bandwidth = estimate_bandwidth(flat_image, quantile=.06, n_samples=3000)
ms = MeanShift(bandwidth, max_iter=800, bin_seeding=True)
ms.fit(flat_image)
labeled=ms.labels_


# get number of segments
segments = np.unique(labeled)
print('Number of segments: ', segments.shape[0])

# get the average color of each segment
total = np.zeros((segments.shape[0], 3), dtype=float)
count = np.zeros(total.shape, dtype=float)
for i, label in enumerate(labeled):
    total[label] = total[label] + flat_image[i]
    count[label] += 1
avg = total/count
avg = np.uint8(avg)

# cast the labeled image into the corresponding average color
res = avg[labeled]
result = res.reshape((img.shape))

# show the result
cv.imshow('result',result)
cv.waitKey(0)
cv.destroyAllWindows()

现在我想将此结果映射到 dto 。 DTO 看起来像

SELECT
  (SELECT COUNT(*) FROM Student as ST, 
  (SELECT COUNT(*) FROM Teacher as TE,
  (SELECT COUNT(*) FROM Subject as SU

存储库调用看起来像 -

public class CountDto{
        Integer student;
        Integer teacher;
        Integer subject;
        }

调用此函数时出现以下错误提示

@Query(value = "SELECT\r\n"
        + "  (SELECT COUNT(*) FROM Student) as ST, \r\n"
        + "  (SELECT COUNT(*) FROM Teacher) as TE,\r\n"
        + "  (SELECT COUNT(*) FROM Subject) as SU", nativeQuery = true)
public CountDto getCount();

我应该如何将我的回复转换为所需的 DTO？

Answer 1

您可以将 CountDto 声明为公共接口，它应该可以工作。就 Spring 而言，它被称为 Projection。或者您可以将 SqlResultSetMapping 或 ConstructorResult 与您的班级一起使用。

您不必通过任何实体类来实现它，即使在存储库文件中也可以像独立接口一样创建它：

public interface StudentRepository extends CrudRepository<Student, Long> {

    @Query(value = "SELECT\r\n"
            + "  (SELECT COUNT(*) FROM Student) as ST, \r\n"
            + "  (SELECT COUNT(*) FROM Teacher) as TE,\r\n"
            + "  (SELECT COUNT(*) FROM Subject) as SU", nativeQuery = true)
    Counts getCount();
    
    public static interface Counts {
        Integer getST();        
        Integer getTE();
        Integer getSU();
    }

}

Answer 2

所以这是要做的答案- DTO 看起来像

public CountDto{
    private Integer studentTotal;
    private Integer teacherTota;
    private Integer subjectTotal;
}

存储库调用 -

@Query(value = "SELECT\r\n"
        + "  (SELECT COUNT(*) FROM Student) as ST, \r\n"
        + "  (SELECT COUNT(*) FROM Teacher) as TE,\r\n"
        + "  (SELECT COUNT(*) FROM Subject) as SU", nativeQuery = true)
public Map<String,Integer> getCount();

最后是serviceImpl--

public CountDto getCount{
        CountDto CountValue = new CountDto();
        Map<String,Integer> map =  repository.getCount();
        for (Map.Entry<String,Integer> entry : map.entrySet())   {
            if(entry.getKey().equals("ST"))
                CountValue.setStudentTotal( entry.getValue());
            if(entry.getKey().equals("TE"))
                CountValue.setTeacherTotal( entry.getValue());
            if(entry.getKey().equals("SU"))
                CountValue.setSubjectTotal( entry.getValue());
        }
        return CountValue ;
}

但解决方案对我来说似乎很复杂。需要任何更简单的方法。

Answer 3

在纯 Hibernate/JPA 用法中，这是一个简单的动态实例化查询（JPA 称之为“构造函数结果”）：

select new CountDTO( 
   (SELECT COUNT(*) FROM Student) as ST,
   ...
)

这里对 Spring 一无所知，尽管有一个警告......在尝试有用时，它经常“妨碍”。不确定这里的情况...您是否尝试过直接 Hibernate/JPA？

将查询结果映射到 dto

3 个答案: