This is to showcase how federation would be used in practice with elixir
Start each of the Elixir federated services in separate terminal windows.
$ cd <products|reviews|inventory>
$ mix deps.get
$ mix phx.server
Start Gateway
$ cd gateway
$ yarn install
$ yarn start
- Gateway http:https://localhost:4000
- Products http:https://localhost:4001
- Reviews http:https://localhost:4002
- Inventory http:https://localhost:4003
defmodule ProductsWeb.Schema do
use Absinthe.Schema
use Absinthe.Federation.Schema
query do
extends()
field :product, :product do
arg(:upc, non_null(:string))
resolve(&resolve_product_by_upc/2)
end
end
object :product do
key_fields("upc")
field(:upc, non_null(:string))
field(:name, non_null(:string))
field(:price, :integer)
end
defp resolve_product_by_upc(%{upc: upc}, _ctx),
do: {:ok, %{upc: upc, name: "Test Product", price: 1000}}
endquery @extends {
product(upc: String!): Product
}
type Product @key(fields: "upc") {
upc: String!
name: String!
price: Int
}defmodule ReviewsWeb.Schema do
use Absinthe.Schema
use Absinthe.Federation.Schema
@reviews [
%{id: 1},
%{id: 2}
]
query do
extends()
field :review, :review do
arg(:id, non_null(:id))
end
end
object :review do
key_fields("id")
field(:id, non_null(:id))
field(:_resolve_reference, :review) do
resolve(&resolve_review_by_id/2)
end
end
object :product do
key_fields("upc")
extends()
field :upc, non_null(:string) do
external()
end
field(:reviews, list_of(:review)) do
resolve(&resolve_reviews_for_product/3)
end
field(:_resolve_reference, :product) do
resolve(&resolve_product_by_upc/2)
end
end
defp resolve_product_by_upc(%{upc: upc}, _ctx),
do:
{:ok,
%{
__typename: "Product",
upc: upc,
reviews: @reviews
}}
defp resolve_review_by_id(%{id: _id}, _ctx), do: {:ok, %{__typename: "Review"}}
defp resolve_reviews_for_product(product, _args, _ctx), do: {:ok, product.reviews}
endquery @extends {
review(id: ID!): Review
}
type Review @key(fields: "id") {
id: ID!
}
type Product @extends @key(fields: "upc") {
upc: String! @external
reviews: [Review]
}defmodule InventoryWeb.Schema do
use Absinthe.Schema
use Absinthe.Federation.Schema
query do
extends()
end
object :product do
key_fields("upc")
extends()
field :upc, non_null(:string) do
external()
end
field(:in_stock, :boolean) do
resolve(&resolve_in_stock_for_product/3)
end
end
defp resolve_in_stock_for_product(%{upc: _upc} = _product, _args, _ctx), do: {:ok, true}
endquery @extends {}
type Product @extends @key(fields: "upc") {
upc: String! @external
inStock: Boolean!
}The meat of this PoC is in the schema.ex of each service and in the absinthe_federation library that pulls in some additional macros