GitHub-style URL matching, with only one query. Is this belt-and-suspenders if ActiveRecord caches the query?

project_lookup_constraint.rb

class ProjectLookupConstraint
  def matches? request
    Project.where(request.params.slice(:account_name, :project_name)).first.tap do |project|
      request.flash.now['project'] = project
    end
  end
end

projects_controller.rb

class ProjectsController < ApplicationController
  expose(:project) { flash.now['project'].decorate }
end

routes.rb

require 'project_lookup_constraint'

MyApp::Application.routes.draw do
  get ':account_name/:project_name' => 'projects#show', constraints: ProjectLookupConstraint.new
end