Cool. It sounds like you probably need to create a GenServer process that you add to your application.ex supervision tree. Inside that GenServer you’ll subscribe to RedixPubsub, and then can take some kind of action when a message arrives. I highly recommend checking out this guide https://elixir-lang.org/getting-started/mix-otp/genserver.html and the pages after it if you’re unclear on how to configure a GenServer within your application.
benwilson512
Author of Craft GraphQL APIs in Elixir with Absinthe
sc4224
So I’ve just created a MyApp.Registry file (AKA my Genserver) which has a handle_info function. This is located in my folder lib/my_app. What do I do in my application.ex?
0
kokolegorille
Registry is an unfortunate name for a GenServer, because You might confuse with Elixir Registry.
Once You have a GenServer, You can use application.ex to start it.
Inside this GenServer, I would use init to subscribe, and handle_info to receive messages from Redis, as mentionned by @benwilson512
0
sc4224
Say I just went ahead with the word registry, should I be adding supervisor(MyApp.Registry.start_link()) to the children array?
0
kokolegorille
No, You should use worker()… supervisor() is for … supervisor.
like this
worker(MyApp.MyGenServer, [])
You don’t need to specify start_link inside.
0
sc4224
So do I do this in the init function?
def init(:ok) do
names = %{}
refs = %{}
{:ok, pubsub} = Redix.PubSub.start_link()
Redix.PubSub.subscribe(pubsub, "my_channel", self())
{:ok, {names, refs}}
end
0
kokolegorille
I would not start Redix.PubSub here, but in application, and before your GenServer starts…
{:ok, pubsub} = Redix.PubSub.start_link()
# instead, put this in application
worker(Redix.PubSub, [])
But the rest seems fine.
0
sc4224
Is this how application.ex should look like?
defmodule MyApp.Application do
use Application
def start(_type, _args) do
import Supervisor.Spec
children = [
supervisor(MyApp.Repo, []),
supervisor(MyAppWeb.Endpoint, []),
worker(Redix.PubSub, []),
]
{:ok, pubsub} = Redix.PubSub.start_link()
opts = [strategy: :one_for_one, name: MyApp.Supervisor]
result = Supervisor.start_link(children, opts)
result
end
def config_change(changed, _new, removed) do
MyAppWeb.Endpoint.config_change(changed, removed)
:ok
end
end
0
kokolegorille
What was the result of your previous try? Apart from not being started by top supervisor, it should have been working.
0
sc4224
it doesn’t listen on port 4000 if I did this
defmodule MyApp.Application do
use Application
def start(_type, _args) do
import Supervisor.Spec
children = [
supervisor(MyApp.Repo, []),
supervisor(MyAppWeb.Endpoint, []),
worker(Redix.PubSub, []),
]
{:ok, pubsub} = Redix.PubSub.start_link()
Redix.PubSub.subscribe(pubsub, "my_channel", self())
receive do
{:redix_pubsub, ^pubsub, :subscribed, %{channel: "my_channel"}} -> :ok
end
receive do
{:redix_pubsub, ^pubsub, :message, %{channel: "my_channel", payload: "hello"}} ->
IO.puts "Received a message!"
end
opts = [strategy: :one_for_one, name: MyApp.Supervisor]
result = Supervisor.start_link(children, opts)
result
end
def config_change(changed, _new, removed) do
MyAppWeb.Endpoint.config_change(changed, removed)
:ok
end
end
0