Question

I’ve got one model with about 50 columns of measurement data, each with a different unit of measurement (ie. grams, ounces, etc.). What is a good way to associate units of measurement with columns in my database? The primary use for this is simply for display purposes. (Ruby on Rails)

EDIT: To clarify, my model is an object, and the attributes are different measurements of that object. So, an example would be if I had the model Car and the attribute columns :power, :torque, :weight, :wheelbase, etc. I would want car.power.unit to return hp and car.weight.unit to return lbs., etc. This way, I would be able to do something like this:

<%= car.power + car.power.unit %>

and it would return

400hp

Answer 1

Updated Answer

Since you’re storing many columns of data, but each column is only one type, and your concern is strictly presentational, I would just use a decorator to accomplish what you need. See this railscast for an example of a great way to do this using Draper.

Basically, a decorator wraps your model with presentation specific methods, so instead of:

#CarsController.rb
def show
  @car = Car.find(params[:id])
end

You would use

#CarsController.rb
def show
  @car = CarDecorator.find(params[:id])
end

You would define a decorator like so:

class CarDecorator < ApplicationDecorator
  decorates :car

  def horsepower
    model.power.to_s + "hp" #call to_s just in case
  end

end

Then in your view any time you called @car.horsepower you would get 123hp instead of 123. In this way you can build a big long reusable list of presentation methods. You can share methods between objects using inheritance, and you can allow methods from the original model to be called as well. See the railscast and the docs etc. You can use Draper or you could roll your own presenter class if you don’t want to use a library.

---

Previous Answer (Abridged):

I can see two nice, easy ways to do this:

1) Just add a text column for units to your data model. IE: to get “400hp” use [data.value,data.units].join

2) You could get a little richer association by having a Units model, perhaps with help from something like ActiveEnum.