hey, i have a situation where we want to use mock ...

# apollo-kotlin

[agrosner]

hey, i have a situation where we want to use mock data and construct them with mock values (custom scalars included)
what we’ve had to do is do nasty workarounds like this:

override fun resolveLeaf(context: FakeResolverContext): Any {
        val mergedField = context.mergedField
        val type = mergedField.type.rawType()
        if (type is CustomScalarType) {
            // workaround the fact that Apollo doesn't have an API for constructing adapters
            // so we dont need explicit dependencies constructed here.
            val adapter = __CustomScalarAdapters.responseAdapterFor<Any>(type)
            if (adapter is AdapterResolver<*, *> && type.className == adapter.outputClass.qualifiedName) {
                @Suppress("UNCHECKED_CAST")
                return (adapter as AdapterResolver<Any, Any>).convert(resolver.resolve(context, adapter.inputClass))
            }
        }

        return super.resolveLeaf(context)
    }

since the default fake resolver does not handle scalar types. should I file a feature request?

[agrosner]

the workaround is making our custom scalar adapters implement interface to convert between things

[agrosner]

/**
 * Workaround for adapters not knowing how to construct their own types.
 */
interface AdapterResolver<Input : Any, Output : Any> {

    val inputClass: KClass<Input>

    val outputClass: KClass<Output>

    fun convert(input: Input): Output
}

[mbonnin]

Not sure I'm following. How do you get your initial mock data?

[mbonnin]

(in all case, if you already have an idea of an API that would help, please file a feature request!)

[agrosner]

sure. we were using data builders to create mock data, returning the operation.data itself ourselves

[agrosner]

passing in a `FakeResolver`:

Someop.Data(resolver = resolver) {

}

to resolve things not explicitly filled in

[agrosner]

we either need to manually provide any scalar field, or use the workaround

[mbonnin]

Do you want to create pseudo random scalars?

[mbonnin]

Apollo Kotlin knows nothing about the internal structure of the scalars nor how they are coerced so there's so much we can do there

[mbonnin]

Say you have a Date scalar, there has to be something that generates stuff like 2025-03-03T14:44:49Z

[Subodh Nijsure]

I have been trying something like this isn't that the intent of FakeRolver?

And then constructing item like this:

val dataResponse = SomeQuery.Data(DateTimeFakeResolver)

object CustomFakeResolver : FakeResolver {
    override fun resolveLeaf(context: FakeResolverContext): Any {
        return when (val leafName = context.mergedField.type.rawType().name) {
            "DateTime" -> DateTimeFormatter.ISO_INSTANT.format(Instant.now())
            "String" -> DataGenerator.randomString()
            <... other stuff>
            else -> error("Don't know how to fake scalar: ${context} ${leafName}")
        }
    }

    override fun resolveListSize(context: FakeResolverContext): Int {
        return Random.nextInt(1, 3) // Generate 1–2 items for lists
    }

    override fun resolveMaybeNull(context: FakeResolverContext): Boolean {
        return false // Don't return nulls by default
    }

    override fun resolveTypename(context: FakeResolverContext): String {
        return context.id
    }

    override fun stableIdForObject(
        obj: Map<String, Any?>,
        mergedField: CompiledField
    ): String? {
        return null
    }
}