How can I get the UTC time when I query mongodb in golang

I am relatively new to Golang and MongoDB and ran into a date issue where it appears that I can insert a UTC date into MongoDB, but when I query through Golang it is getting automatically converted to the local time. I want to get it back from MongoDB in UTC with no conversion. Here is a quick example:

type SampleItem struct {
	ObjId      bson.ObjectId `bson:"_id,omitempty" json:"-"`
	SampleDate time.Time     `bson:"sampleDate" json:"sampleDate"`
}

func TestMe() {

	var item SampleItem
	var items []SampleItem

	sess := getSession()
	defer sess.Close()

	item.SampleDate = time.Now().UTC()
	fmt.Printf("%s\n", item.SampleDate)

	collection := sess.DB("myCollection").C("sampleItems")
	collection.Insert(item)

	err := collection.Find(bson.M{}).All(&items)
	if err == nil {
		fmt.Printf("%s\n", items[0].SampleDate)
	}
}

My output:

> 2014-10-12 04:10:50.3992076 +0000 UTC
>
> 2014-10-11 23:10:50.399 -0500 CDT

It appears that the mgo driver may be automatically converting it because when I query mongodb from a console window my date is in UTC. Am I missing a mgo option somewhere that turns this off?

Go time.Time values store an instant in time and a location. The mgo BSON decoder sets the location to time.Local.

You can set time.Local to the UTC location:

time.Local = time.UTC

A package designed to be used third parties should not modify the local location, but it's OK within the scope of an application.

The Time.UTC() method returns a time at the same instant in time as the receiver and the location set to UTC. This line will print the time in UTC:

    fmt.Printf("%s\n", items[0].SampleDate.UTC())

Because MongoDB stores time with lower precision than a time.Time, the value returned from MongoDB may not equal the value you stored.

I know I asked this question, but after lots of digging around I found this to be one possible option. By using a custom type from time.Time you can override the json serializer interfaces and force the use of UTC. However, is doing this type of thing recommended...

I have to give some credit to UNIX time stamps in Golang as well as the go source.

type JsonTime time.Time
func (t JsonTime) MarshalJSON() ([]byte, error) {
tt := time.Time(t).UTC()
if y := tt.Year(); y < 0 || y >= 10000 {
return nil, errors.New("JsonTime: year outside of range [0,9999]")
}
if y := tt.Year(); y == 1 {
return []byte{}, nil
}
return []byte(tt.Format(`"` + time.RFC3339Nano + `"`)), nil
}
func (t JsonTime) GetBSON() (interface{}, error) {
if time.Time(t).IsZero() {
return nil, nil
}
return time.Time(t), nil
}
func (t *JsonTime) SetBSON(raw bson.Raw) error {
var tm time.Time
if err := raw.Unmarshal(&tm); err != nil {
return err
}
*t = JsonTime(tm)
return nil
}
func (t JsonTime) String() string {
return time.Time(t).UTC().String()
}
type SampleItem struct {
ObjId      bson.ObjectId `bson:"_id,omitempty" json:"-"`
SampleDate JsonTime      `bson:"sampleDate" json:"sampleDate"`
}
func TestMe() {
var item SampleItem
var items []SampleItem
sess := getSession()
defer sess.Close()
item.SampleDate = JsonTime(time.Now().UTC())
fmt.Printf("%s\n", item.SampleDate)
collection := sess.DB("myCollection").C("sampleItems")
collection.Insert(item)
err := collection.Find(bson.M{}).All(&items)
if err == nil {
fmt.Printf("%s\n", items[0].SampleDate)
if data, err := json.Marshal(items); err != nil {
fmt.Printf("%v\n", err)
} else {
fmt.Printf("%s\n", data)
}
}
}