Routing constraints tied to your app without breaking reloading in development mode

routes.rb

# Sometimes Constraints need to interact with controllers (fex. in order not to query the database twice), then I like
# to put them inside the controller. If you load controllers from your routes.rb (more precisely, when routes.rb is loaded),
# these won't reload in development mode.
# If your constraints live somewhere else (say, /app/constraints), it's basically all the same.

# This demonstrates an easy workaround by wrapping the fetching of constraints in a block:

class ConstraintWrapper
  # Helps to load constraints from inside controllers without breaking
  # development environment reloading

  def initialize(&block)
    @constraint_factory = block
  end

  def matches?(request)
    @constraint_factory.call.matches?(request)
  end
end

Blog::Application.routes.draw do
  get '*url', to: 'my_controller#page', constraints: ConstraintWrapper.new { MyController::Constraint.new }
end