如何在MongoDB的Golang中找到一个字段的最大值？

huangapple
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英文:

How to find maximum value of a field in mongodb golang?

问题

这是我的代码。即使有更多的块（例如3000个块），我总是得到最大值999。

这是文档的样子。

如何在MongoDB的Golang中找到一个字段的最大值？

  2. func GetLatestBlockFromMongoDB() int{
  3. 	if contains(ReturnBlocksExists(), "blocks") == true {
  4. 		ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
  5. 		var blockheights []models.Block
  6. 		defer cancel()
  7. 	
  8. 		options := options.Find().SetProjection(bson.M{"block.header.blockNumber": 1})
  10. 		options.SetSort(bson.D{{"block.header.blockNumber", -1}})
  12. 		options.SetLimit(1)
  13. 	
  14. 		results, err := blocksCollections.Find(context.TODO(), bson.D{}, options)
  15. 	
  16. 		if err != nil {
  17. 			fmt.Println(err)
  18. 		}
  19. 	
  20. 		//以最优方式从数据库中读取
  21. 		defer results.Close(ctx)
  22. 		for results.Next(ctx) {
  23. 			var singleBlock models.Block
  24. 			if err = results.Decode(&singleBlock); err != nil {
  25. 				fmt.Println(err)
  26. 			}
  27. 	
  28. 			blockheights = append(blockheights, singleBlock)
  29. 		}
  30. 		fmt.Println("%v", blockheights[0].Block.Header.BlockNumber)
  31. 		if len(strings.TrimSpace(blockheights[0].Block.Header.BlockNumber)) > 0{
  32. 			i, err := strconv.Atoi(blockheights[0].Block.Header.BlockNumber)
  33. 			if err != nil {
  34. 				glog.Fatalf("%v", err)
  35. 			}
  36. 			return i
  37. 		} else {
  38. 			return 0
  39. 		}
  40. 	} else {
  41. 		return 0
  42. 	}
  43. }

我如何获得blockNumber的最大值？我认为问题可能是blockNumber是一个字符串而不是整数。我不确定。我已经设置了排序和限制为1，所以它应该正常工作。

英文:

This is my code. I always get maximum value of 999, even when there are more blocks (e.g 3000 blocks).

This is what the document(s) look like.

如何在MongoDB的Golang中找到一个字段的最大值？

  2. func GetLatestBlockFromMongoDB() int{
  3. 	if contains(ReturnBlocksExists(), "blocks") == true {
  4. 		ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
  5. 		var blockheights []models.Block
  6. 		defer cancel()
  7. 	
  8. 		options := options.Find().SetProjection(bson.M{"block.header.blockNumber": 1})
  10. 		options.SetSort(bson.D{{"block.header.blockNumber", -1}})
  12. 		options.SetLimit(1)
  13. 	
  14. 		results, err := blocksCollections.Find(context.TODO(), bson.D{}, options)
  15. 	
  16. 		if err != nil {
  17. 			fmt.Println(err)
  18. 		}
  19. 	
  20. 		//reading from the db in an optimal way
  21. 		defer results.Close(ctx)
  22. 		for results.Next(ctx) {
  23. 			var singleBlock models.Block
  24. 			if err = results.Decode(&singleBlock); err != nil {
  25. 				fmt.Println(err)
  26. 			}
  27. 	
  28. 			blockheights = append(blockheights, singleBlock)
  29. 		}
  30. 		fmt.Println("%v", blockheights[0].Block.Header.BlockNumber)
  31. 		if len(strings.TrimSpace(blockheights[0].Block.Header.BlockNumber)) > 0{
  32. 			i, err := strconv.Atoi(blockheights[0].Block.Header.BlockNumber)
  33. 			if err != nil {
  34. 				glog.Fatalf("%v", err)
  35. 			}
  36. 			return i
  37. 		} else {
  38. 			return 0
  39. 		}
  40. 	} else {
  41. 		return 0
  42. 	}
  43. }

How can i get the maximum value of blockNumber? I think the problem might be because blockNumber is a string but not an integer. I'm not sure. I did set sort and also limit 1 so it should normally work.

答案1

得分: 2

是的，你说得对，从图像中我可以看到blockNumber字段是一个字符串，所以你不是在比较整数，而是在比较字符串，其中"999"大于"3000"：

例如：

  1. package main
  3. import (
  4. 	"fmt"
  5. )
  7. func findMax(a []string) string {
  8. 	m := a[0]
  9. 	for _, value := range a {
  10. 		if value > m {
  11. 			m = value
  12. 		}
  13. 	}
  14. 	return m
  15. }
  17. func main() {
  18. 	blocks := []string{"999", "2000", "3000"}
  19. 	ma := findMax(blocks)
  20. 	fmt.Println(ma)
  21. }
  1. $ go run .
  2. 999

还可以查看这个问题。

英文:

Yes, you are right, from the image, I can see that the blockNumber field is a string, so you are not comparing integers, you are comparing string, where "999" is greater than "3000":

For example:

  1. package main
  3. import (
  4. 	"fmt"
  5. )
  7. func findMax(a []string) string {
  8. 	m := a[0]
  9. 	for _, value := range a {
  10. 		if value > m {
  11. 			m = value
  12. 		}
  13. 	}
  14. 	return m
  15. }
  17. func main() {
  18. 	blocks := []string{"999", "2000", "3000"}
  19. 	ma := findMax(blocks)
  20. 	fmt.Println(ma)
  21. }
  1. $ go run .
  2. 999

Check out this question too.

huangapple
  • 本文由 发表于 2022年7月2日 03:26:34
  • 转载请务必保留本文链接：https://go.coder-hub.com/72833835.html
  • go
  • mongodb
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