Did something in 4.0.0-alpha.15 change (vs. 3.7.0) in regards to resolving nullable query/mutation p...

# graphql-kotlin

[Robert]

Did something in 4.0.0-alpha.15 change (vs. 3.7.0) in regards to resolving nullable query/mutation parameter?

@GraphQLDescription("performs some operation")
    fun doSomething(
        @GraphQLDescription("super important value")
        value: Int?
    ): Boolean = true

this works ✅

query {
  doSomething(value:null) {
    ..
  }
}

this fails in 4.0.0-alpha.15 ❗ : no argument provided for a required parameter: parameter #1 query of fun SomeQuery.doSomething(<http://kotlin.Int?|kotlin.Int?>) and works with 3.7.0

query {
  doSomething {
    ..
  }
}

it works again when using a default

@GraphQLDescription("performs some operation")
    fun doSomething(
        @GraphQLDescription("super important value")
        value: Int? = null
    ): Boolean = true

[Dariusz Kuc]

Yeah I think it was a side effect of fixing context handling and now nullable fields require explicit default null value.

@Shane Myrick do you remember the details around it?

[Dariusz Kuc]

Ah yes you found the pr -> https://github.com/ExpediaGroup/graphql-kotlin/pull/981#issuecomment-803290175

[Shane Myrick]

Ah, yes. I see what happened here. This could be fixed by modifying the function data fetcher

[Shane Myrick]

I remember why I did this now. If we check to see if the argument is not present in the GraphQL request and then pass in null to the function in that case, we will not be able to use Kotlin default values

[Shane Myrick]

I could make this change: https://github.com/ExpediaGroup/graphql-kotlin/compare/master...smyrick:null-on-missing-args?expand=1

But then this unit test no longer works and neither will default values.

https://github.com/smyrick/graphql-kotlin/blob/c5b8fdc3739930f712a114b9abc15dee8fc[…]diagroup/graphql/generator/execution/FunctionDataFetcherTest.kt

[Shane Myrick]

Since we can’t inspect if a KParameter has a default value, we can only support one use case or the other.

• Support Kotlin default values but require them for nullable input
• Do not support Kotlin default values and always pass null for input if argument is missing in request

[Dariusz Kuc]

With null default we also cannot determine whether null was passed explicitly or was not present -> have to use the wrapper

[Dariusz Kuc]

I think supporting default values (even though it requires explicit null) is probably more useful

[Shane Myrick]

Yea, so then in that case it is a breaking change to 4.0.0. We haven’t really well documented the full list of changes from 3.x.x yet

[Robert]

you guys already have a place where you want to document that?
Could provide the example there as a PR if you like

[Dariusz Kuc]

I believe https://expediagroup.github.io/graphql-kotlin/docs/schema-generator/writing-schemas/arguments#optional-fields should be updated