how to point __resolveReference method to _resolveReference?

[girishramnani]

Hi,
So as per this doc https://www.apollographql.com/docs/apollo-server/using-federation/api/apollo-subgraph/#__resolvereference the __resolveReference has to be called ( and it cannot be changed ) and not _resolveReference so I am not able to make it work, is there a config need to be changed?

[kdawgwilk]

The gateway should never be calling that resolver directly but should use the _entities(...) field instead. Are you seeing the gateway calling __resolveReference when trying to resolve entities? If that's the case it would be a breaking change to the federation spec and I am not aware of any breaking changes. What version of the gateway/router are you running?

[girishramnani]

We are using apollographql/router:v1.2.0 so 1.2.0 version and yeah I can see that __resolveReference is being called. But also isn't that what the docs say that thats what will be called?

[kzlsakal]

__resolveReference is a function implementation specific to Apollo Server. Apollo Router shouldn't be making any GQL queries for a __resolveReference field. Field names that start with __ are reserved for introspection only as it's stated here and here.

If you follow the "Defining an entity" link in that Apollo Server documentation, it says ⚠️ This section describes how to create reference resolvers in Apollo Server. If you're using another subgraph-compatible library, see its documentation for creating reference resolvers. here.

There is an example repository with multiple entity examples and tests in Elixir if it would be helpful.

[abhilashr2021]

When i tried following the above approach, it throw me with below error

  ** (FunctionClauseError) no function clause matching in Absinthe.Middleware.unshim/2

     The following arguments were given to Absinthe.Middleware.unshim/2:
     
         # 1
         [{Absinthe.Middleware.Telemetry, []}, {{Absinthe.Resolution, :call}, &MyApp.V2.Graphql.Resolvers.Books.get_books/3}]

There was a similar issue faced by another person, and he mentioned the below approach
https://github.com/tobiasbernet/elixir_federation

i had to change the resolver enclosed inside anonymnous function call.

field(:_resolve_reference, :book) do
      resolve(fn _, args, _ -> Books.get_books(nil, args, nil) end)
    end

but the resulting output is %{data: %{"_entities" => [%{}]}}
instead of respective book object

[kzlsakal]

where is the field definition of that _resolve_reference?

If you define it under the correct object definition like this

query do
end

object :book do
  extends()
  key_fields("id")

  field :id, :id do
    external()
  end

  field :name, :string

  field :_resolve_reference, :book do
    resolve(fn _, args, _ -> Books.get_book(nil, args, nil) end)
  end
end

then run a query like this:

query GetBookEntities($representations: [_Any]) {
  _entities(representations: $representations) {
    ... on Book {
      name
      id
      __typename
    }
  }
}

with variables: {"representations": [{"id": "foo", "__typename": "Book"}]}

it would resolve the entity's fields

[kzlsakal]

We added a test to demonsrate how _resolve_reference works but we can keep this issue open to address the case with the named function usage for the resolver.

[tristantreb]

I had the same issue and solved it by using an anonymous function (as per @abhilashr2021's comment - thanks!)

Why doesn't it work with function capturing?

resolve(&Books.get_books/3)

[kdawgwilk]

@tristantreb its likely due to the complexities of the compile-time magic that absinthe is doing and how it captures those references using macros. I do think its solvable and we should see if we can get a fix for it

[kzlsakal]

Why doesn't it work with function capturing?

This will be fixed by #104