Add JSON to shopspring-numeric extension

ext/shopspring-numeric/decimal.go

@@ -11,6 +11,7 @@ import (
 )
 
 var errUndefined = errors.New("cannot encode status undefined")
+var errBadStatus = errors.New("invalid status")
 
 type Numeric struct {
 	Decimal decimal.Decimal
@@ -316,3 +317,32 @@ func (src Numeric) Value() (driver.Value, error) {
 		return nil, errUndefined
 	}
 }
+
+func (src Numeric) MarshalJSON() ([]byte, error) {
+	switch src.Status {
+	case pgtype.Present:
+		return src.Decimal.MarshalJSON()
+	case pgtype.Null:
+		return []byte("null"), nil
+	case pgtype.Undefined:
+		return nil, errUndefined
+	}
+
+	return nil, errBadStatus
+}
+
+func (dst *Numeric) UnmarshalJSON(b []byte) error {
+	d := decimal.NullDecimal{}
+	err := d.UnmarshalJSON(b)
+	if err != nil {
+		return err
+	}
+
+	status := pgtype.Null
+	if d.Valid {
+		status = pgtype.Present
+	}
+	*dst = Numeric{Decimal: d.Decimal, Status: status}
+
+	return nil
+}