# GraphQL adapter for Yggdrasil
[](https://travis-ci.org/etherharvest/yggdrasil_graphql) [](https://hex.pm/packages/yggdrasil_graphql) [](https://hex.pm/packages/yggdrasil_graphql)
This project is a GraphQL adapter for `Yggdrasil` publisher/subscriber.
## Small example
Let's say we want to have the following GraphQL `subscription`:
```graphql
subscription {
events(channel: "my_channel") {
content
}
}
```
And we have a process in Elixir that, using `Yggdrasil`, generates the
following event:
```
Yggdrasil.publish(
%Yggdrasil.Channel{name: "my_channel"},
%{content: "some message"}
)
```
Using [Absinthe](https://github.com/absinthe-graphql/absinthe), our Schema
would look like this:
```elixir
defmodule MyAppWeb.Schema do
use Absinthe.Schema
object :message do
field :content, :string
end
query do
end
subscription do
field :events, :message do
arg :channel, non_null(:string)
config fn args, %{context: %{pubsub: endpoint}} ->
channel = %Yggdrasil.Channel{name: args.channel}
Yggdrasil.GraphQL.subscribe(endpoint, :events, channel)
end
end
end
end
```
## Phoenix setup
> This is an extract from
> [this guide](https://hexdocs.pm/absinthe/subscriptions.html) modified
> slightly to fit this example.
1. Add the `Absinthe` libraries:
```elixir
{:absinthe, "~> 1.4"},
{:absinthe_phoenix, "~> 1.4"},
```
2. Add the `Phoenix.PubSub` configuration for your endpoint:
```elixir
config :my_app, MyAppWeb.Endpoint,
# ... other config
pubsub: [
name: MyApp.PubSub,
adapter: Phoenix.PubSub.PG2
]
```
3. In your application supervisor, add a line **after** your existing endpoint
supervision line:
```elixir
[
# other children ...
supervisor(MyAppWeb.Endpoint, []), # this line should already exist.
supervisor(Absinthe.Subscription, [MyAppWeb.Endpoint]), # add this line
# other children ...
]
```
Where `MyAppWeb.Endpoint` is the name of your application’s phoenix endpoint.
4. In your `MyAppWeb.Endpoint` module add:
```
use Absinthe.Phoenix.Endpoint
```
5. In your socket add:
- **Phoenix 1.3**
```elixir
use Absinthe.Phoenix.Socket, schema: MyAppWeb.Schema
```
- **Phoenix 1.2**
```
use Absinthe.Phoenix.Socket
def connect(_params, socket) do
socket = Absinthe.Phoenix.Socket.put_schema(socket, MyAppWeb.Schema)
{:ok, socket}
end
```
And that should be enough to have a working subscription setup.
## GraphQL adapter
The GraphQL adapter has the following rules:
* The `adapter` name is identified by the atom `:graphql`.
* The channel `name` must be a tuple with the `endpoint` name,
the subscription `field` and an `Yggdrasil` channel to any of the available
adapters.
* The `transformer` must encode to a map. It is recommended to leave the
encoding and decoding to the underlying adapter. Defaults to `:default`
transformer.
* The `backend` is and always should be `:graphql`.
The function `Yggdrasil.GraphQL.subscribe/3` is in charged of creating the
channel and generating the topic for` Absinthe`.
## Installation
Using this GraphQL adapter with `Yggdrasil` is a matter of adding the available
hex package to your `mix.exs` file e.g:
```elixir
def deps do
[{:yggdrasil_graphql, "~> 0.1"}]
end
```
## Relevant projects used
* [Absinthe](https://github.com/absinthe-graphql/absinthe): GraphQL
toolkit for Elixir
## Author
Alexander de Sousa.
## License
`yggdrasil_graphql` is released under the MIT License. See the LICENSE file for
further details.
