Rendering 404s from empty streams

projected_with mirrors ActiveRecord#find end to end. On a hit it returns an instance of the projection’s materialization model, ready for the view to render. On a miss it raises ActiveRecord::RecordNotFound — and because Rails already maps that exception to a 404 response, a show action that calls projected_with renders the host app’s 404 page with no rescue code, no helper layer, no custom controller plumbing.

# app/controllers/debts_controller.rb
class DebtsController < ApplicationController
  def show
    @debt = DebtEventStream.for(params[:id]).projected_with(DebtProjection)
  end
end

@debt is whatever DebtProjection materializes — an ActiveRecord row or an ActiveModel instance. Whatever shape the projection produces is the same shape the view receives, so the rest of the show template is straight Rails.

A miss can come from any of three places: an unknown stream id, a known stream with no events, or a known stream whose events all fall outside the as_of: / at: window you asked for.

DebtEventStream.for("unknown-id").projected_with(DebtProjection)
# => raises ActiveRecord::RecordNotFound

stream = DebtEventStream.for("debt-123")
stream.projected_with(DebtProjection, at: Time.new(1999, 1, 1))
# => raises ActiveRecord::RecordNotFound if every event occurred after Jan 1, 1999

Funes also writes a Rails.logger.info line before raising, so your logs record which stream, projection, and filter values led to the empty result.