Hello `Koliners` I want ask about `SecurityByDesign` if there better setup how to create the classes...

# announcements

[marzelwidmer]

Hello Koliners I want ask about SecurityByDesign if there better setup how to create the classes https://gist.github.com/marzelwidmer/6aa9733c919f2a8dc6aa84116fe4a580 what I don’t like is… invoke function is available

data class Customer (val firstName: FirstName, val lastName: LastName, val gender: Gender)
// Domain Primitive
data class FirstName private constructor(val value: String) {
    companion object {
        // Create Object
        operator fun invoke(value: String) = FirstName(validate(value = value))
        private fun validate(value: String): String {
            check(value.isNotEmpty()) { "value must be non-empty" }
            check(value.trim().length >= 2) { "wrong value length" }
            check(value.trim().length <= 20) { "wrong value length" }
            return value
        }
    }
}

[nanodeath]

why even have an invoke method? just use the constructor.

[nanodeath]

(with an init block that does the validation)

[diesieben07]

You can run validation in init Block of a data class:

data class FirstName(val value: String) {
  init {
    require(value.isNotEmpty()) { ... }
  }
}

[marzelwidmer]

@ParameterizedTest(name = "{index} test gender {0}")
    @ValueSource(chars = ['f', 'F', 'm', 'M'])
    fun `Customer creation test - it must have a valid gender fF 👧 or mM 🧔`(input: Char) {
        Customer(firstName = FirstName(Faker().name.firstName()), lastName = LastName(Faker().name.lastName()), gender = Gender(input))
    }

I it posible to hide it

[diesieben07]

Also consider using require instead of check, as it throws IllegalArgumentException

[nanodeath]

also I'd be careful about making these data classes...I always forget if it's possible to safeguard the copy method

[Marc Knaup]

Btw, I’ve used a similar pattern before but it didn’t scale well.

Validation logic cannot always be specified on the type in a static way. It may be dynamic (depend on other input) and/or have complex business logic. So I ended up removing all length checks and alike from these types.

[Marc Knaup]

copy is guarded by init afaik.

[diesieben07]

init can never be bypassed (unless you hack the JVM)

[Marc Knaup]

Also, static validation on the type tends to be problematic when (de)serializing and when migrating data. Validation logic may change over time which makes it super hard to reuse those classes.

You also may re-run expensive validation in cases where data is known to be valid, e.g. when coming from DB.

[nanodeath]

@diesieben07 all the more reason to use init instead of a factory method then :)

[marzelwidmer]

The init setup I like … muchos gracias 🙂 @Marc Knaup what U mean to reuse those classes I am working in a a like microservice setup… was planing to validate the Bounded Context with this. how U do it then with the validations ?

[Marc Knaup]

If it’s just a small microservice it may actually be fine.

I have a validation behind separate interfaces, not part of the data model.
My data model is used multiplatform and for serialization (API & database). Having the validation logic involved in all of those turned out to be problematic 😁

[Marc Knaup]

Let’s say you limit FirstName to 20 chars (which is ridiculous btw 😉) and store such data to DB.

In the future you want to limit to 19 chars, so you change the validation.

What happens to old users loaded from DB? They may have 20 chars.

[marzelwidmer]

Is more foucs at REST layer (for web and mobile clients) this is just a PoC setup with DB basically we have to send it later to external system and other services in our domain. and at the moment we can’t trust (;) all the client calls 😉 and have to some how protect the (external system) to also don’t get many issues who is for difficult to analyse then

[Marc Knaup]

Is it a public API?
How do you communicate the validation failures to the API client?

[marzelwidmer]

no is private corporate API

[marzelwidmer]

the communication on rest level. we use the https://github.com/zalando/problem

[Marc Knaup]

So in that case it’s probably okay to communicate the IllegalArgumentException message to the client :)

[marzelwidmer]

yes.. i think so… important is to don’t pass it (if something missing on first place) to other service in special to the Backend of the company

[marzelwidmer]

with this I mean what leave our product team (owned services)

[Marc Knaup]

Makes sense 👍