reduce code duplication of DTOs validations - oop

Question

I have the following two data classes
data class CreateMedicDto(
val firstName: String,
val lastName: String,
val pin: String,
val address: String?,
val birthDate: LocalDate,
val specialty: Specialty,
)
data class UpdateMedicDto(
val firstName: String,
val lastName: String,
val address: String?,
val birthDate: LocalDate,
val specialty: Specialty,
)
The only difference is that the second one is missing pin field. The reason for that is that in case of update I do not want to allow the possibility to change the pin by using making use of the language and framework features.
Currently, in this form, I will need to validate both of them:
fun validateMedic(
input: CreateMedicDto,
): MedicValidationResult? {
with(input) {
if (checkLengthBetween1And50(input.firstName)) return MedicValidationResult.InvalidFirstNameLength
if (checkLengthBetween1And50(input.lastName)) return MedicValidationResult.InvalidLastNameLength
address?.let {
if (checkLengthGreaterThan500(it)) return MedicValidationResult.InvalidAddressLength
}
if (checkDateValidity(birthDate)) return MedicValidationResult.InvalidBirthDate
}
return null
}
fun validateMedic(
input: UpdateMedicDto,
): MedicValidationResult? {
with(input) {
if (checkLengthBetween1And50(input.firstName)) return MedicValidationResult.InvalidFirstNameLength
if (checkLengthBetween1And50(input.lastName)) return MedicValidationResult.InvalidLastNameLength
address?.let {
if (checkLengthGreaterThan500(it)) return MedicValidationResult.InvalidAddressLength
}
if (checkDateValidity(birthDate)) return MedicValidationResult.InvalidBirthDate
}
return null
}
The code is almost identical, only the input parameter type is different.
The question is how can I reduce it to a single function?
I have some solutions but there are also some reasons for that I would not like to use them:
Inherit CreateMedicDto from UpdateMedicDto. This may easily solve the problem but it doesn't really make much sense to say that CreateMedicDto is an UpdateMedicDto
Make that pin field nullable. With this approach I abandon the language null-safety feature and I am going to rely on a parameter which says "create" or "update"
Both extending a common class. The third class is actually useless and can't find a proper name for it
Any better approaches to still benefit from the type safety?

Answer 1

Your option 3 is called an abstract class. abstract means it cannot be instantiated, but also that it can have abstract members (properties and functions with no implementation or initial value).
An option 4 would be to create a common interface for both of them.
But in both cases, there will still be duplication of all the property names because you have to override them. But it fixes the duplication at your validation functions.
Option 3 example:
abstract class MedicDto {
abstract val firstName: String
abstract val lastName: String
abstract val pin: String
abstract val address: String?
abstract val birthDate: LocalDate
abstract val specialty: Specialty
}
data class CreateMedicDto(
override val firstName: String,
override val lastName: String,
val pin: String,
override val address: String?,
override val birthDate: LocalDate,
override val specialty: Specialty,
): MedicDto()
data class UpdateMedicDto(
override val firstName: String,
override val lastName: String,
override val address: String?,
override val birthDate: LocalDate,
override val specialty: Specialty,
): MedicDto()
Option 4 example:
interface MedicDto {
val firstName: String
val lastName: String
val pin: String
val address: String?
val birthDate: LocalDate
val specialty: Specialty
}
data class CreateMedicDto(
override val firstName: String,
override val lastName: String,
val pin: String,
override val address: String?,
override val birthDate: LocalDate,
override val specialty: Specialty,
): MedicDto
data class UpdateMedicDto(
override val firstName: String,
override val lastName: String,
override val address: String?,
override val birthDate: LocalDate,
override val specialty: Specialty,
): MedicDto