Code to render a view from inside a model

model.rb

  def render_to_string
    I18n.with_locale(locale) do
      Renderer.render(
        file: "purchase_mailer/invoice", 
        layout: nil, 
        assigns: { charge: self, purchase: purchase, product: product, account: account, payments: payments }
      )
    end
  end

renderer.rb

class Renderer
  def self.render(options)
    (@@renderer ||= self.new).render(options)
  end
  
  def view_context_class
    Class.new(ActionView::Base) do
      include ApplicationHelper
      include EmailHelper
      include Rails.application.routes.url_helpers
    end
  end

  def _prefixes
    []
  end
    
  def render(options)
    view_context_class.new(ActionController::Base.view_paths, options.delete(:assigns), self).render(options)
  end
end