I am a complete novice to Elixir, Phoenix and functional programming itself. I am quite overwhelmed by the whole file structure you get when starting with Phoenix. To get to know it a little better, I want to do the following:
I have a Model called Document. It holds some metadata for files that exist locally on my machine (field “filename” in the model). I also added a config value documents_path where those documents are supposedly stored. On startup (or ideally in a set interval), I want to verify whether the Documents in the database and the local files match up (does the file locally exist? If not, we should get rid of the database entry).
I have several questions now:
Where do I put my function (lets assume its named verify_document_cache). Do I put it in the DocumentController?
1.1 If not, where do I put it and how do I gain access to the Repo so I can call Repo.all, or do I create a helper for that somewhere else?
Is it the “correct” way to run it from the lib/my_app.ex file as stackoverflow suggests?
2.1 How do I “include” the DocumentController (or whereever I will implement the function)? I tried require Myapp.DocumentController or just require DocumentController but the compiler complains that they do not exist.
There are multiple ways to do it. One that makes sense to me is add a process which will verify_document_cache on an interval basis. Since I’d like to make sure the process is restarted when it crashes, I would add it to a supervisor and make it a GenServer (like more in line with other OTP stuff).
You’ll already find some gen_server supervised in lib/my_app.ex (like App.Repo).
You could then write a GenServer and put it in lib/document_verifier.ex:
defmodule MyApp.DocumentVerifier do
alias MyApp.Repo
require Logger
use GenServer
def start_link do
GenServer.start_link(__MODULE__, [name: __MODULE__])
end
def init(_) do
Process.send_after(self, :verify_docs, 5 * 60 * 1000) #5 min, 60 sec, 1000 millisecs
{:ok, []}
end
def handle_info(:verify_docs, state) do
verify_docs
Process.send_after(self, :verify_docs, 5 * 60 * 1000) # reschedule job after 5min
{:noreply, state}
end
defp verify_docs do
# use stuff from Repo etc to verify your docs
end
end
