Hi, TL;DR I have data classes that contain nullab...

# getting-started

[huehnerlady]

Hi,

TL;DR I have data classes that contain nullables but no default values. can I add these default values retrospectively without touching the data class itself, like through an extention function or something in that direction?

long version:

I have a lib which includes generated data classes. Unfortunately this lib has a lot of nullables and for test purpose I need to instantiate those classes. That means that I have a constructor with currently 51 nulls. I
f I fill one value in and then add some data to the generated class, the parameter order might shift and then it is a pain to find out in which of the 51 positions I need to add the value. It is a real paini, it is on the radar of the generator to add default values, but for now I cannot change this behaviour in the data class directly.

Is there a way to add add these default values retrospectively without touching the data class itself, like through an extention function or something in that direction I can use in the meantime?? it might be hacky but I cannot imagine it being as hacky as 50/51 null values per test case 😓

[Sylvain Moindron]

you can create an extention function wich call the construtor. in your function give a default value for each parameter and in your unit test call the non null parameter with name.

[huehnerlady]

@Sylvain Moindron thank you for your quick response

that does sound like a hacky solution, but at least I have the adaption and the 51 nulls in just one place.

I think I will do this for now, does anybody have an idea of a different, maybe a bit less verbose solution?

[Milan Hruban]

you can also not have class with 51 constructor parameters 🙂 but apart from that I think that the solution above is good

[huehnerlady]

As I say I have a generated class so I cannot change that. This data class is generated from a graphql query. And for production code this works fine as the mapping is all done inside the library. But for testing my interaction with it and mocking certain responses I need to instantiate a class, and as there are no default values there is just one huge constructor unfortunately.

As I said I did ask them to change this and so hopefully in future this will be not neccessary. BUT in the Meantime I have the problem that I have very very hard to read code. And as I am very new to kotlin I thought there is a way. So I will now do the way @Sylvain Moindron mentioned and hopefully they fix it soon.

If there is a different way after all I would be very interested to hearing about it though 🙂

[huehnerlady]

@Sylvain Moindron @Milan Hruban Can I create an overload contructor for the data class itself? so that the data class has 2 constructors in the end? Currently the only way I could find was to create a helper function which gives you a new object back. but would be cool to somehow extend the data class the way that you can use that function as an alternative constructor 🙂

[Milan Hruban]

you can create constructors only for the classes that you own. I think "helper" function is fine, since you are talking about tests. Maybe have a look at fake constructors https://blog.kotlin-academy.com/effective-java-in-kotlin-item-1-consider-static-factory-methods-instead-of-constructors-8d0d7b5814b2

[huehnerlady]

@Milan Hruban sorry, maybe I was not clear enough. for me using the 52 nulls is theoretically fnie as it is a test. but I ran into this issue and I thought I try to find out what options there are in kotlin. so again - the helper funktion works (already implemented it) BUT then again maybe there is somethin kotlin-specific, so I can learn more kotlin-style with my ‘problems’

So the last hint is a real treat, thank you so much @Milan Hruban

Unfortunately I seem not to be able to get this to work


So I guess the generate classes are not really kotlin style so it seems very difficult to use them in a kotlin way.
I have a structure like this in a file “Api.kt”:

class TestSuperClass {
  data class SomeTestClass(val property1: String?, val property2: String?)
}

Then I try to create a function for tests in a file “Extentions.kt” looking like this:

import de.europace.pm.edge.api.legacy.TestSuperClass.SomeTestClass

inline fun SomeTestClass(property1: String? = null): SomeTestClass = SomeTestClass(property1 = property1, property2 = null)

When I then try to call that funktion in my test though, it cannot be found and I get the compile errors

No value passed for parameter 'property1'
No value passed for parameter 'property2'

When The data class is outside the TestSuperClass, it works as expected with the overloaded constructor.

So is that a limitation or is there a tweak I have to add to my extention function for it to work?
I could totally understand if that is not possible, as it seems odd to generate the data classes inside the other class, but I cannot change that yunfortunately as I am too happy for the other way it works with graphql to change it bcause I do not like the way to write tests 😅

[Milan Hruban]

try this

inline fun SomeTestClass(property1: String? = null): TestSuperClass.SomeTestClass = TestSuperClass.SomeTestClass(property1 = property1, property2 = null)

[thanksforallthefish]

alternatively, instead of instantiating your class, you could mock it.

val myDataClass = mockk<DataClass>{
  every { property } returns "something"
} //for instance, with <http://mockk.io|mockk.io>

this way it is also clear which of the values are actually used in which specific use case

[huehnerlady]

@thanksforallthefish ah interesting alternative, thank you, I use mockk already and I am very happy with it, so yes that is a good alternative indeed 🙂

I am kind of interested in the solution by @Milan Hruban though as I want to practice more n my Extension skills, coming from Java I am still learing the imense flexibility it gives you 🙂

[Matteo Mirk]

If I fill one value in and then add some data to the generated class, the parameter order might shift and then it is a pain to find out in which of the 51 positions I need to add the value.

this is the exactly one of the problems that named arguments were meant solve