Custom marshal/unmarshal leveraging Scan/Value() for JSON and Database usage

the_marshal.go

package main

import (
	"database/sql/driver"
	"encoding/json"
	"fmt"
	"strings"
)

type paymentOption int64

const (
	// PaymentOptionUnknown is an invalid type
	PaymentOptionUnknown paymentOption = iota
	// PaymentOptionCard means a card payment was made
	PaymentOptionCard
	// PaymentOptionInstalments means an instalment plan was used
	PaymentOptionInstalments
)



// Begin cancer

func (x paymentOption) String() string {
	return map[paymentOption]string{
		PaymentOptionUnknown:     "PaymentOptionUnknown",
		PaymentOptionCard:        "PaymentOptionCard",
		PaymentOptionInstalments: "PaymentOptionInstalments",
	}[x]
}

// Scan ...
func (x *paymentOption) Scan(value interface{}) error {
	db := value.([]uint8)
	// An attempt to fetch a map value with a key that is not present in
	// the map will return the zero value for the type of the entries in the map i.e.
	// the unknown option

	*x = map[string]paymentOption{
		"PaymentOptionUnknown":     PaymentOptionUnknown,
		"PaymentOptionCard":        PaymentOptionCard,
		"PaymentOptionInstalments": PaymentOptionInstalments,
	}[string(db)]
	return nil
}

// Value ...
func (x paymentOption) Value() (driver.Value, error) {
	return x.String(), nil
}


// MarshalJSON Converts to Byte array
func (x paymentOption) MarshalJSON() ([]byte, error) {
	return json.Marshal(strings.ToLower(strings.ReplaceAll(x.String(), "PaymentOption", "")))
}

// UnmarshalJSON Converts from byte array
func (x *paymentOption) UnmarshalJSON(b []byte) error {
	var j string
	if err := json.Unmarshal(b, &j); err != nil {
		return err
	}
	// Cancer hacks
	return x.Scan([]uint8((fmt.Sprintf("PaymentOption%s", strings.Title(j)))))
}

// end cancer

type Test struct {
	Bar []paymentOption `json:"bar"`
}

func main() {
	data := []byte(`{"bar": ["instalments","card"]}`)
	var test Test
	var err error
	json.Unmarshal(data, &test)
	fmt.Printf("After unmarshal: %#v %s\n", test, test)

	test.Bar = []paymentOption{PaymentOptionInstalments}
	data, err = json.Marshal(test)
	fmt.Println(">",err)
	fmt.Printf("After marshal: %#v %s\n", string(data), data)
}