absinthe-subscriptions

# Absinthe - Subscriptions

Guide to implementing real-time GraphQL subscriptions with Absinthe and Phoenix.

## Key Concepts

### Basic Setup

```elixir
# In your Phoenix endpoint
defmodule MyAppWeb.Endpoint do
  use Phoenix.Endpoint, otp_app: :my_app
  use Absinthe.Phoenix.Endpoint

  socket "/socket", MyAppWeb.UserSocket,
    websocket: true,
    longpoll: false
end

# Socket configuration
defmodule MyAppWeb.UserSocket do
  use Phoenix.Socket
  use Absinthe.Phoenix.Socket, schema: MyApp.Schema

  def connect(params, socket, _connect_info) do
    current_user = get_user_from_token(params["token"])
    socket = Absinthe.Phoenix.Socket.put_options(socket,
      context: %{current_user: current_user}
    )
    {:ok, socket}
  end

  def id(socket), do: "user_socket:#{socket.assigns.user_id}"
end
```

### Defining Subscriptions

```elixir
defmodule MyApp.Schema.Subscriptions do
  use Absinthe.Schema.Notation

  object :post_subscriptions do
    field :post_created, :post do
      config fn _args, _resolution ->
        {:ok, topic: "posts"}
      end

      trigger :create_post, topic: fn _post ->
        "posts"
      end
    end

    field :post_updated, :post do
      arg :id, non_null(:id)

      config fn %{id: id}, _resolution ->
        {:ok, topic: "post:#{id}"}
      end

      trigger :update_post, topic: fn post ->
        "post:#{post.id}"
      end
    end
  end
end
```

### Publishing from Mutations

```elixir
defmodule MyApp.Resolvers.Post do
  def create_post(_parent, %{input: input}, _resolution) do
    case MyApp.Posts.create_post(input) do
      {:ok, post} ->
        # Publish to subscription
        Absinthe.Subscription.publish(
          MyAppWeb.Endpoint,
          post,
          post_created: "posts"
        )
        {:ok, post}
      {:error, changeset} ->
        {:error, changeset}
    end
  end
end
```

### User-Specific Subscriptions

```elixir
field :user_notification, :notification do
  config fn _args, %{context: %{current_user: user