Create a collection called idgen, create a document for every other collection, and store the self-add id

mongo-id-generator.go

// Create a collection called idgen, create a document for every other collection,
// and store the self-add id

import (
	"context"
	"go.mongodb.org/mongo-driver/bson"
	"go.mongodb.org/mongo-driver/mongo"
	"go.mongodb.org/mongo-driver/mongo/options"
)

type idGenerate struct {
	ID  int
	KEY string
}

func Next(coll string) (int, error) {
	update := bson.M{"$inc": bson.M{"id": 1}}
	idG := idGenerate{ID: 1}
	err := database.Collection("idgen").
		FindOneAndUpdate(context.Background(), bson.M{"key": coll}, update).Decode(&idG)
	if err == mongo.ErrNoDocuments {
		_, err := database.Collection("idgen").InsertOne(context.Background(), bson.M{"key": coll, "id": 1})
		if err != nil {
			ec <- err
			return 0, nil
		} else {
			return 0, nil
		}
	} else if err != nil {
		ec <- err
		return 0, err
	} else {
		return idG.ID, nil
	}
}