查找所有时间戳少于10秒的mongo db文档

Question

I am trying to get all mongo db documents with timestamps less than 10 seconds ago. I am not finding any. I think this is because my time format is not correct. I am not finding them querying mongo db from shell db.mgo.find({timestamp:{$gt: new Date(ISODate().getTime() - 86400)}}) for last 24h.

// FindLast 10min
func FindLast(session *mgo.Session, db, collection string) ([]Syslog, error) {
  var results []Syslog
  t := time.Now().Add(-10 * time.Second)
  c := session.DB(db).C(collection)
  err := c.Find(
    bson.M{
        "timestamp": bson.M{
            "$gt": t,         
        },
  }).All(&results)
  return results, err
}

If I pick one of document ObjectId("...").getTimestamp() it shows ISODate("2017-08-25T19:14:54Z") which is about 4h ahead of me so it is UTC. But even if I change to UTC in my func it still not finding any documents

t := time.Now().UTC().Add(-time.Duration(10)*time.Minute).Format("2006-01-02 15:04:05")

Answer 1

But even if I change to UTC in my func it still not finding any documents

This is because there is no field timestamp within your document. The query syntax that you're using is equivalent to ask select all documents where timestamp is greater than T from the collection.

I assume that what you're meaning to do is to use the timestamp value derived from the ObjectId of every documents using getTimestamp() method. If this is the case, you can utilise mgo/bson function NewObjectIdWithTime() see example as below:

currentTime := time.Now()
queryTime := currentTime.Add(-10 * time.Second)

// Generate a dummy ObjectId with a specified timestamp for querying
var oidtime = bson.NewObjectIdWithTime(queryTime)
query := bson.M{"_id": bson.M{"$gt": oidtime}}
err := collection.Find(query).All(&documents)

The above reversed your querying, instead of using time to query we utilises ObjectId to query. Otherwise you would have to fetch every document, convert their ObjectId's to timestamp and compare, which may not be as efficient.

Alternatively, depending on your use case you can add a timestamp value for each document using $currentDate operator to set the value of a field to the current date.