为什么在bson.Marshal和bson.Unmarshal之后time.Time不相等？

Question

Why does it output false? I was expecting true...

package main
import (
    "fmt"
    "time"
    "gopkg.in/mgo.v2/bson"
    )

type S struct {
    T time.Time
}
func main() {
    t := S{time.Now()}
    bytes, _ := bson.Marshal(t)
    var dt S
    bson.Unmarshal(bytes, &dt)
    fmt.Println(dt.T.Equal(t.T))
}

go run the above will output false, why Marshal/Unmarshal doesn't preserve the original value?

Answer 1

Bson stores time with lower precision than a time.Time, the value returned from Bson may not equal the value you stored. You need to use bson.Now():

package main

import (
    "fmt"
    "gopkg.in/mgo.v2/bson"
    "time"
)

type S struct {
    T time.Time
}

func main() {
    t := S{bson.Now()}
    bytes, _ := bson.Marshal(t)
    var dt S
    bson.Unmarshal(bytes, &dt)
    fmt.Println(dt.T)
    fmt.Println(t.T)
    fmt.Println(dt.T.Equal(t.T))
}

Output:

$> go run main.go 
2018-09-08 10:48:42.45 +0300 MSK
2018-09-08 10:48:42.45 +0300 MSK
true