key_fields_must_exist validation errors

[kdawgwilk]

I was working on updating the https://github.com/apollographql/apollo-federation-subgraph-compatibility elixir implementation to use more recent versions and to fix CI and I am now seeing errors with this validation phase.

== Compilation error in file lib/products_web/schema.ex ==
** (UndefinedFunctionError) function :product_variation.of_type/0 is undefined (module :product_variation is not available)
    :product_variation.of_type()
    (absinthe_federation 0.2.4) lib/absinthe/federation/schema/phase/validation/key_fields_must_exist.ex:75: Absinthe.Federation.Schema.Phase.Validation.KeyFieldsMustExist.validate_nested_key/5
    (elixir 1.13.4) lib/enum.ex:2396: Enum."-reduce/3-lists^foldl/2-0-"/3
    (absinthe 1.7.0) lib/absinthe/blueprint/transform.ex:16: anonymous fn/3 in Absinthe.Blueprint.Transform.prewalk/2
    (absinthe 1.7.0) lib/absinthe/blueprint/transform.ex:109: Absinthe.Blueprint.Transform.walk/4
    (elixir 1.13.4) lib/enum.ex:1715: Enum."-map_reduce/3-lists^mapfoldl/2-0-"/3
    (elixir 1.13.4) lib/enum.ex:1715: Enum."-map_reduce/3-lists^mapfoldl/2-0-"/3
    (absinthe 1.7.0) lib/absinthe/blueprint/transform.ex:139: anonymous fn/4 in Absinthe.Blueprint.Transform.walk_children/5
    (elixir 1.13.4) lib/enum.ex:2396: Enum."-reduce/3-lists^foldl/2-0-"/3
    (absinthe 1.7.0) lib/absinthe/blueprint/transform.ex:114: Absinthe.Blueprint.Transform.walk/4
    (absinthe 1.7.0) lib/absinthe/blueprint/transform.ex:15: Absinthe.Blueprint.Transform.prewalk/2
    (absinthe_federation 0.2.4) lib/absinthe/federation/schema/phase/validation/key_fields_must_exist.ex:16: Absinthe.Federation.Schema.Phase.Validation.KeyFieldsMustExist.handle_schemas/2
    (absinthe 1.7.0) lib/absinthe/blueprint/transform.ex:16: anonymous fn/3 in Absinthe.Blueprint.Transform.prewalk/2
    (absinthe 1.7.0) lib/absinthe/blueprint/transform.ex:109: Absinthe.Blueprint.Transform.walk/4
    (elixir 1.13.4) lib/enum.ex:1715: Enum."-map_reduce/3-lists^mapfoldl/2-0-"/3
    (absinthe 1.7.0) lib/absinthe/blueprint/transform.ex:139: anonymous fn/4 in Absinthe.Blueprint.Transform.walk_children/5
    (elixir 1.13.4) lib/enum.ex:2396: Enum."-reduce/3-lists^foldl/2-0-"/3
    (absinthe 1.7.0) lib/absinthe/blueprint/transform.ex:114: Absinthe.Blueprint.Transform.walk/4
    (absinthe 1.7.0) lib/absinthe/blueprint/transform.ex:15: Absinthe.Blueprint.Transform.prewalk/2
    (absinthe_federation 0.2.4) lib/absinthe/federation/schema/phase/validation/key_fields_must_exist.ex:11: Absinthe.Federation.Schema.Phase.Validation.KeyFieldsMustExist.run/2

I think this may have to do with the field and field type name not being the same? the field is called variation but its type is product_variation

[kdawgwilk]

Actually this error is from this line

absinthe_federation/lib/absinthe/federation/schema/phase/validation/key_fields_must_exist.ex

Line 75 in a8c828d

object = field && Absinthe.Blueprint.Schema.lookup_type(bp, field.type.of_type)

the of_type only exists if the type is non_null so this blows up for nullable fields which prompts the question can @key(fields: "...") reference nullable fields?

[kdawgwilk]

Kaden Wilkinson Jun 24th at 11:38 AM

Federation spec question: Can @key(fields: "…") reference nullable fields or do they have to be non null fields in order to be keys?

Lenny 1 day ago

the query planner can certainly send an entity reference like { __typename: "Product", id: null } to a subgraph but that might be weird for the subgraph’s entity resolver to handle

Derek 1 day ago

All the examples I've seen show them as non-nullable but I think they potentially could be nullable (as there could be multiple @keys).

Derek 1 day ago

Lenny -> would it make sense to make a guarantee from the router that the values would never be null? (as I agree having null key would be rather hard to resolve)

[kzlsakal]

According to the messages, currently, a nullable key field is still valid. What other methods can we use to accomplish this type lookup?