Using custom display values in Simple Form

Simple Form is a popular library for Rails that makes it easy to generate forms using a simple DSL, while adding high customisability.

I had to create a dropdown select element today where the display values had to be different to the actual values selected behind the scenes. Checking the docs, I found that Simple Form has a label_method property that can be used for just this purpose, though they don’t explicitly explain how. I tinkered around with it and figured it out, so for posterity, here is an example:

simple_form_for @qualification do |f|
    = f.input :year_of_study,
        collection: 1..4,
        label_method: ->(i) { i == 4 ? "final year" | "#{i.ordinalize} year" }

This example would result in a select that selects from [1, 2, 3, 4], but displays ["1st year", "2nd year", "3rd year", "final year"].

This is a rather nifty feature and I’m surprised they don’t document it a bit better, but hey, now you know. :)