Absinthe.Federation

Apollo Federation support for Absinthe

Installation

Install from Hex.pm:

def deps do
  [
    {:absinthe_federation, "~> 0.5"}
  ]
end

Install from github:

def deps do
  [
    {:absinthe_federation, github: "DivvyPayHQ/absinthe_federation", branch: "main"}
  ]
end

Add the following line to your absinthe schema

defmodule MyApp.MySchema do
  use Absinthe.Schema
+ use Absinthe.Federation.Schema

  query do
    ...
  end
end

Usage

Macro based schemas (recommended)

Note: Implementing the reference resolver with function capture does not work at the moment. Hence, the below example uses an anonymous function.

defmodule MyApp.MySchema do
  use Absinthe.Schema
+ use Absinthe.Federation.Schema

  query do
+   extends()

    field :review, :review do
      arg(:id, non_null(:id))
      resolve(&ReviewResolver.get_review_by_id/3)
    end
    ...
  end

  object :product do
+   key_fields("upc")
+   extends()

    field :upc, non_null(:string) do
+     external()
    end

    field(:reviews, list_of(:review)) do
      resolve(&ReviewResolver.get_reviews_for_product/3)
    end

+   field(:_resolve_reference, :product) do
+     resolve(fn parent, args, context ->
        ProductResolver.get_product_by_upc(parent, args, context)
      end)
+   end
  end
end

Macro based schema with existing prototype

If you are already using a schema prototype

defmodule MyApp.MySchema do
  use Absinthe.Schema
+ use Absinthe.Federation.Schema, prototype_schema: MyApp.MySchemaPrototype

  query do
    ...
  end
end

defmodule MyApp.MySchemaPrototype do
  use Absinthe.Schema.Prototype
+ use Absinthe.Federation.Schema.Prototype.FederatedDirectives

  directive :my_directive do
    on [:schema]
  end
end

SDL based schemas (experimental)

defmodule MyApp.MySchema do
  use Absinthe.Schema
+ use Absinthe.Federation.Schema

  import_sdl """
    extend type Query {
      review(id: ID!): Review
    }

    extend type Product @key(fields: "upc") {
      upc: String! @external
      reviews: [Review]
    }
  """

  def hydrate(_, _) do
    ...
  end

Resolving structs in _entities queries

If you need to resolve your struct to a specific type in your schema you can implement the Absinthe.Federation.Schema.EntityUnion.Resolver protocol like this:

defmodule MySchema do
  @type t :: %__MODULE__{
          id: String.t()
        }

  defstruct id: ""

  defimpl Absinthe.Federation.Schema.EntityUnion.Resolver do
    def resolve_type(_, _), do: :my_schema_object_name
  end
end

Federation v2

You can import Apollo Federation v2 directives by extending your top-level schema with the @link directive.

defmodule MyApp.MySchema do
  use Absinthe.Schema
  use Absinthe.Federation.Schema

+ extend schema do
+   directive :link,
+     url: "https://specs.apollo.dev/federation/v2.0",
+     import: [
+       "@key",
+       "@shareable",
+       "@provides",
+       "@external",
+       "@tag",
+       "@extends",
+       "@override",
+       "@inaccessible"
+     ]
+ end

  query do
    ...
  end
end

Namespacing and directive renaming with @link

@link directive supports namespacing and directive renaming (only on Absinthe >= 1.7.2) according to the specs.

defmodule MyApp.MySchema do
  use Absinthe.Schema
  use Absinthe.Federation.Schema

+ extend schema do
+   directive :link,
+     url: "https://specs.apollo.dev/federation/v2.0",
+     import: [%{"name" => "@key", "as" => "@primaryKey"}], # directive renaming
+     as: "federation" # namespacing
+ end

  query do
    ...
  end
end

More Documentation

See additional documentation, including guides, in the Absinthe.Federation hexdocs.

Contributing

Refer to the Contributing Guide.

License

See LICENSE