NickName:gempir Ask DateTime:2018-09-23T15:40:13

Marshalling time.Time to unix timestamp

I have a struct like so

type log struct {
    [...]
    Timestamp timestamp `json:"timestamp"`
}

and I want to have the Timestamp as unix timestamp instead of whatever go does by default (2018-09-21T19:31:03.291Z)

I've tried creating a custom type for that like this:

type timestamp struct {
    time.Time
}

func (t timestamp) MarshalJSON() ([]byte, error) {
    return []byte(strconv.FormatInt(time.Time(t.Time).Unix(), 10)), nil
}

func (t *timestamp) UnmarshalJSON(data []byte) error {
    i, err := strconv.ParseInt(string(data[:]), 10, 64)
    if err != nil {
        return err
    }
    t = &timestamp{
        time.Unix(i, 0),
    }
    return nil
}

but I'm always getting the error can not unmarshal timestamp into *main.timestamp when trying to read from the database.

for iter.Scan(&message.Text, &message.Timestamp) {

    userlogResult.Messages = append(userlogResult.Messages, message)
}
if err := iter.Close(); err != nil {
    log.Error(err)
}

It can't unmarshall the Timestamp here. https://github.com/gocql/gocql/blob/799fb0373110eaa4e2e71dd32a9b5903f80dca8f/helpers.go#L30 the issue is that it doesn't use the Unmarshall functions.

Edit: I've answered my own question.

Copyright Notice：Content Author:「gempir」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/52464058/marshalling-time-time-to-unix-timestamp

Answers

Sarath Sadasivan Pillai 2018-09-23T09:09:51

here when assigning &timestamp{..} to t it is changing the pointer instead the value it is pointed to has to be chaged as follows\n\nfunc (t *timestamp) UnmarshalJSON(data []byte) error {\n i, err := strconv.ParseInt(string(data[:]), 10, 64)\n if err != nil {\n return err\n }\n *t = timestamp{\n time.Unix(i, 0),\n }\n return nil\n}\n\n\nPlease find code here\n\nEdit\n\nSince you are failing to unmarshall when reading from Database it is not because of json.unmarshalling you have to implement sql.Scanner\nif you are using sql \n\nPlease find the details here => sql.Scanner",

Oliver Jackman 2018-09-23T09:21:18

I think your code is ok - apart from the code in your unmarshal. You don't show the code where you are Marshalling/Unmarshalling which is where the actual error is.\n\nI have it working on the playground. Golang Playground\n\nInstead of this (which changes the pointer)\n\nt = &timestamp{\n time.Unix(i, 0),\n}\n\n\nChange the value\n\nt.Time = time.Unix(i,0)\n\n\nMain function to use your structs\n\nfmt.Println(\"First Log...\")\nl := log{Timestamp: timestamp{time.Now()}}\nfmt.Println(l)\n\nbuf, err := json.Marshal(l)\nif err != nil {\n panic(err)\n}\nfmt.Println(\"Marshalled to JSON...\")\nfmt.Printf(\"%s\\n\", buf)\n\nvar logCopy log\nif err := json.Unmarshal(buf, &logCopy); err != nil {\n panic(err)\n}\nfmt.Println(\"UnMarshalled from JSON...\")\nfmt.Println(logCopy)\n",