time.Time encoded as map[string]interface{}{}

[smyrman]

Noticed that if encoding a struct into a map, time.Time entries are passed into empty maps, which doesn't seam very useful.

I could add a hook to encode it into a string instance, but because hooks run as pre-processors, it's not possible to preserve it as a time.Time.

Example code:

package main

import (
	"fmt"
	"time"

	"github.com/mitchellh/mapstructure"
)

func PayloadEncoder(target *map[string]interface{}) (*mapstructure.Decoder, error) {
	return mapstructure.NewDecoder(&mapstructure.DecoderConfig{
		//DecodeHook: mapstructure.ComposeDecodeHookFunc(
		// <- no hook can be added here to solve this.
		//),
		Result: target,
	})
}

type MyStruct struct {
	CreatedAt time.Time
}

func main() {
	p1 := MyStruct{
		CreatedAt: time.Now(),
	}
	m1 := make(map[string]interface{})
	d1, err := PayloadEncoder(&m1)
	fmt.Println("\nerr:", err, "\ndec:", d1, "\nmap:", m1)
	err2 := d1.Decode(p1)
	fmt.Printf("\nerr: %v\noutput: %#v\n", err2, m1)
}

Output:

err: <nil> 
dec: &{0xc0001be000} 
map: map[]

err: <nil>
output: map[string]interface {}{"CreatedAt":map[string]interface {}{}}

[Dragomir-Ivanov]

Hi @smyrman ,
Have you considered using "github.com/fatih/structs"?

https://play.golang.org/p/rFTAG5bcUI4

[mitchellh]

I believe #183 should address this.

[yjwong]

Hello @mitchellh, firstly, thanks for this library. I've been trying to achieve something similar, converting from a struct into a map[string]interface{} while preserving time.Time fields, but looking at the changes in #183, I wasn't entirely sure how to do it.

I tried setting a new reflect.Value to the to argument but it seems like we can't change the type of a reflect.Value.

Are there any examples/hints on how this can be achieved?

[smyrman]

Agree with @yjwong; I don't quite see how #183 allows solving this problem.

The problem is that after DecodeHookExec is run, then mapstructure would still run through the "default" transitions, in which case it will find that it is converting a time.Time to an interface{} value, and convert it to an empty map[string]interface{}.

[mimol91]

Having this same issue

[MessageDream]

Having this same issue

[gatspy]

mark this issue

[johnny-oriente]

Same issue

[Dragomir-Ivanov]

@johnny-oriente I recommend using struct2 for conversion from struct -> map[string]interface{}.
https://github.com/worldline-go/struct2

[Dragomir-Ivanov]

@smyrman, Hi there! This new https://github.com/worldline-go/struct2 package may be of interest to you too.

[smyrman]

We have work-around this issue long ago by writing our own implementation of the struct / slice -> map[string]interface{} / []interface{} conversion path, and using mapstructure for the to struct path only.

The struct2 omitnested struct tag might work as a way to fix the problem for others though (if you can live with their interface naming; not a topic for this issue).

[Dragomir-Ivanov]

@smyrman They are new kid on the block, so they might be willing to clean up. Their interface is not that big though, so renaming might be easy.