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

Question

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.

Answer 1

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
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