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。
func GetLatestBlockFromMongoDB() int{
if contains(ReturnBlocksExists(), "blocks") == true {
ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
var blockheights []models.Block
defer cancel()
options := options.Find().SetProjection(bson.M{"block.header.blockNumber": 1})
options.SetSort(bson.D{{"block.header.blockNumber", -1}})
options.SetLimit(1)
results, err := blocksCollections.Find(context.TODO(), bson.D{}, options)
if err != nil {
fmt.Println(err)
}
//以最优方式从数据库中读取
defer results.Close(ctx)
for results.Next(ctx) {
var singleBlock models.Block
if err = results.Decode(&singleBlock); err != nil {
fmt.Println(err)
}
blockheights = append(blockheights, singleBlock)
}
fmt.Println("%v", blockheights[0].Block.Header.BlockNumber)
if len(strings.TrimSpace(blockheights[0].Block.Header.BlockNumber)) > 0{
i, err := strconv.Atoi(blockheights[0].Block.Header.BlockNumber)
if err != nil {
glog.Fatalf("%v", err)
}
return i
} else {
return 0
}
} else {
return 0
}
}
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.
func GetLatestBlockFromMongoDB() int{
if contains(ReturnBlocksExists(), "blocks") == true {
ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
var blockheights []models.Block
defer cancel()
options := options.Find().SetProjection(bson.M{"block.header.blockNumber": 1})
options.SetSort(bson.D{{"block.header.blockNumber", -1}})
options.SetLimit(1)
results, err := blocksCollections.Find(context.TODO(), bson.D{}, options)
if err != nil {
fmt.Println(err)
}
//reading from the db in an optimal way
defer results.Close(ctx)
for results.Next(ctx) {
var singleBlock models.Block
if err = results.Decode(&singleBlock); err != nil {
fmt.Println(err)
}
blockheights = append(blockheights, singleBlock)
}
fmt.Println("%v", blockheights[0].Block.Header.BlockNumber)
if len(strings.TrimSpace(blockheights[0].Block.Header.BlockNumber)) > 0{
i, err := strconv.Atoi(blockheights[0].Block.Header.BlockNumber)
if err != nil {
glog.Fatalf("%v", err)
}
return i
} else {
return 0
}
} else {
return 0
}
}
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：
package main
import (
"fmt"
)
func findMax(a []string) string {
m := a[0]
for _, value := range a {
if value > m {
m = value
}
}
return m
}
func main() {
blocks := []string{"999", "2000", "3000"}
ma := findMax(blocks)
fmt.Println(ma)
}
$ go run .
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:
package main
import (
"fmt"
)
func findMax(a []string) string {
m := a[0]
for _, value := range a {
if value > m {
m = value
}
}
return m
}
func main() {
blocks := []string{"999", "2000", "3000"}
ma := findMax(blocks)
fmt.Println(ma)
}
$ go run .
999
Check out this question too.
通过集体智慧和协作来改善编程学习和解决问题的方式。致力于成为全球开发者共同参与的知识库，让每个人都能够通过互相帮助和分享经验来进步。
评论