How do you run a mailer only after a user has been redirected, in a controller?

Question

For example, if the mailer send_signup_mail is heavy and takes a while to complete, how can I make sign_in_and_redirect execute first and send the mail in the background after the view has been rendered.

In the code below this would just require executing things in linear order, but I assume that's not what's actually happening as the redirect doesn't complete until after the mail has been sent.

class Users::OmniauthCallbacksController < Devise::OmniauthCallbacksController

    def facebook
        # You need to implement the method below in your model (e.g. app/models/user.rb)
        @fb_response = request.env["omniauth.auth"]
        @user = User.from_omniauth(@fb_response)

        if @user.persisted?
          # Update user token
          @user.fb_token = @fb_response.credentials.token
          # Sign in
          sign_in_and_redirect @user, :event => :authentication #this will throw if @user is not activated
          set_flash_message(:notice, :success, :kind => "Facebook") if is_navigational_format?
          # Deliver signup mail
          UserNotifier.send_signup_email(@user).deliver
        else
          session["devise.facebook_data"] = request.env["omniauth.auth"]
          redirect_to new_user_registration_url
        end
    end

end

Thanks!

Answer 1

You should use background job to send emails so that it won't influence user experience. I would suggest you to look into this gem:

Delayed Job

Once you config this gem correctly, you just need to use

UserNotifier.delay.send_signup_email(@user)

to get your email delivered on background.