Support custom JSON unmarshaling and json.Unmarshaler interface in decoding

[Perlence]

Can I have a http.Response as result of GET request? I want to do custom JSON unmarshalling.

[huandu]

Can you please let me know your scenario? Why do you need to do custom JSON unmarshalling?

[Perlence]

I'm requesting user's feed GET me/feed and I need to decode objects in data into structs, that have field CreatedTime of type pq.NullTime. The way decoder works, it asserts that value at created_time must be an object.

I couldn't think of any better solution other than break my struct in two: one that has not null fields, and second that embeds first struct plus field CreatedTime of pq.NullTime. Then I decode post into first struct and embed it, then decode field created_time in second struct.

All this feels very clunky, I think it would be pretty convenient to implement json.Unmarshaler interface for my NullTime.

[huandu]

I see. If this package provides an interface facebook.Unmarshaler just like what json package implements, is it OK for you?

[Perlence]

I guess that would resolve the problem.

[huandu]

Fine. I'll implement it soon.

[huandu]

@Perlence I implemented it in latest master code. Please take a look and have a try.

[Perlence]

Thank you!

When I implemented json.Unmarshaler interface for the whole struct it worked:

type FeedResult struct {
    Data   []FacebookPost `json:"data"`
    Paging Paging         `json:"paging"`
}

type FacebookPost struct {
    ID          string      `json:"id" db:"id"`
    EntryID     int64       `json:"entry_id" db:"entry_id"`
    Message     string      `json:"message" db:"message"`
    Story       string      `json:"story" db:"story"`
    CreatedTime pq.NullTime `json:"created_time" db:"created_time"`
}

func (p *FacebookPost) UnmarshalJSON(data []byte) error {
    var aux struct {
        ID          string   `json:"id" db:"id"`
        Message     string   `json:"message" db:"message"`
        Story       string   `json:"story" db:"story"`
        CreatedTime NullTime `json:"created_time" db:"created_time"`
    }
    ...
}

type NullTime struct{ pq.NullTime }

func (nt *NullTime) UnmarshalJSON(data []byte) error {
    t, err := time.Parse(dateFmt, string(data))
    if err != nil {
        return errors.Trace(err)
    }

    nt.Time = t
    nt.Valid = !t.IsZero()
    return nil
}

Yeah, I know there's facebook.PagingResult, but I must be able to set paging params myself, e.g. from DB. Anyways, I'm more than happy with such approach, it works fine.
But if I implement json.Unmarshaler only for a field, it does not:

type FeedResult struct {
    Data   []FacebookPost `json:"data"`
    Paging Paging         `json:"paging"`
}

type FacebookPost struct {
    ID          string   `json:"id" db:"id"`
    EntryID     int64    `json:"entry_id" db:"entry_id"`
    Message     string   `json:"message" db:"message"`
    Story       string   `json:"story" db:"story"`
    CreatedTime NullTime `json:"created_time" db:"created_time"`
}

type NullTime struct{ pq.NullTime }

func (nt *NullTime) UnmarshalJSON(data []byte) error {
    ...
}

I get error "field 'data.0.created_time' is not a json object in result." I guess, that's expected.

[huandu]

It's a bug in my latest commit. I'll fix it soon.

[huandu]

@Perlence Please take a look at latest master code again. Thanks.

[Perlence]

Yep, it works, thanks 😄