Support custom types for IDs and attributes

[xcoulon]

The library only supports string, int(8,16,32,64) or uint(8,16,32,64) for ID and other non-complex struct attributes, but it would be nice to have a mean to support other types, such as UUIDs, although they require the use of third-party libraries such as https://github.com/satori/go.uuid. This would save the developers to have to convert from string to UUID in the their code.

Since it's not possible to support all third party libraries in https://github.com/google/jsonapi, a solution could be to provide a public function to register custom types that can be marshalled to/unmarshalled from a string.

[xcoulon]

@aren55555, may I ask if could you give a look at my PR (#115) and let me know if it's something you'd be interested in including in the library, please ?

[tprost]

Why is it necessary to have developers register the type? Perhaps any types that implement MarshalJSON() and UnmarshalJSON(), or even just String() should be usable out of the box?

[aren55555]

I'll elaborate on what @tprost mentioned: an interface based approach (similar to what Go's standard encodijng/json library supports) would be the ideal way to solve this problem. See json.Marshaler and json.Unmarshaler for reference.

Granted for the UUID type @xcoulon mentioned, you'd need to embed this in your own custom type and implement the interface, or ask the package maintainer to support implementing the interface. However I think it's a bit farfetched to expect every package's custom types to support the interfaces you desire. Based on the Godoc it appears the UUID type doesn't even implement the standard encoding/json lib's json.Marshaler or json.Unmarshaler interfaces, and it's doubtful they would implement an interface declared by this jsonapi package.

[fosple]

@aren55555 What is the proposed solution to use uuids and jsonapi? I tried to implement my own type with MarshalJSON, UnmarshalJSON & String, however, never got it to work.

This is my starting point:

package example

import (
	"fmt"
	"net/http"

	"github.com/google/jsonapi"
	"github.com/google/uuid"
	"gorm.io/driver/postgres"
	"gorm.io/gorm"
)

type DBUsers struct {
	ID uuid.UUID `gorm:"type:uuid;default:gen_random_uuid();primaryKey" jsonapi:"primary,users"`
}

func GetUsers(w http.ResponseWriter, r *http.Request) {

	db, _ := gorm.Open(postgres.Open("postgres://..."), &gorm.Config{})

	users := []*DBUsers{}
	db.Find(&users)

	if err := jsonapi.MarshalPayload(w, users); err != nil {
		respondWithError(w, http.StatusInternalServerError, "Failed to marshal payload: "+err.Error())
	}

}

It always returns: Failed to marshal payload: id should be either string, int(8,16,32,64) or uint(8,16,32,64)

Caused by

jsonapi/response.go

Line 21 in 1e07b10

"id should be either string, int(8,16,32,64) or uint(8,16,32,64)")