Why are @key annotations enforced for types implementing interface?

[klys-equinix]

I have an interface with an entity resolver like

interface Asset @key(fields: "id") {
    id: ID! # read only
    ...
}

And several types implementing it. Some of them are referenced from external schemas, and so they get their own @EntityMapping, but most are not.

If I do not add a @key annotation, i will get

Caused by: com.apollographql.federation.graphqljava.exceptions.MissingKeyException: Object Ups does not specify @key fields specified by its interface Asset

for

type Ups implements Asset & ElecAsset {
    id: ID!

Why is it enforced like that?

[klys-equinix]

@bclozel Could you take a look?

[bclozel]

Sorry for the delay @klys-equinix .

Spring for GraphQL does check for entity mappings but will throw an IllegalStateException if the setup is considered as invalid. This does seem like this exception is thrown from the federation library directly. Maybe this is a requirement enforced by the library itself?

This would help if you could share a complete stacktrace and elaborate on why you consider this constraint as enforced by Spring for GraphQL and not the federation library.

Thanks!

[klys-equinix]

Fair point, i asked the question here
apollographql/federation-jvm#441

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