By “composing emails” I mean building a Bamboo.Email (or Swoosh.Email) struct (e.g. by YourApp.UserEmail.welcome_email) with all the data (to:, subject:, body:) necessary to send the email:
user
|> YourApp.UserEmail.welcome_email() # => composing an email here
|> YourApp.Mailer.deliver_later() # => delivering the email here, maybe asynchronously
Composing an email often involves making additional calls to the database or third-party APIs to gather necessary data to render the body of the email. Both in Bamboo and in Swoosh, this is done in the caller process by default, effectively blocking it. And if you’re composing an email inside a database transaction (which I believe you shouldn’t) and some error occurs, the transaction might be rolled back, which can be undesirable.
The other approach is to introduce a dedicated Oban worker for composing and sending emails.
defmodule YourApp.Workers.Mailer do
use Oban.Worker, queue: "mailers"
@impl Oban.Worker
def perform(%{"module" => module, "name" => name, "args" => args}, _job) do
module = String.to_existing_atom(module)
name = String.to_existing_atom(name)
module
|> apply(name, args)
|> YourApp.Mailer.deliver_now()
end
end
With YourApp.Workers.Mailer, you can send emails like this:
%{"module" => YouApp.UserEmail, "name" => :welcome_email, "args" => [user.id]}
|> YourApp.Workers.Mailer.new()
|> Oban.insert()
So now if composing an email fails with a transient error (e.g., a network error), it will eventually succeed because Oban will restart the job. If it fails because of a bug in the code, you can always fix the bug and restart the failed job manually (assuming your Oban pruning settings allow it). You can also safely enqueue this job inside a database transaction now.
