Custom currency input for Simple Form

Today, I was moving a standard Rails form to Simple Form and realized that one of the form inputs is actually a Bootstrap input group, with an add-on at the beginning of the input field with the proper currency symbol.

There’s no built-in way to replicate this with Simple Form, but the documentation suggests building a currency Custom Input to show the currency symbol.

In my case, I wanted to be able to pass the symbol as a parameter to the input and have it generate the appropriate markup for Bootstrap.

Here’s the custom input class I ended up adding to app/inputs:

class CurrencyInput < SimpleForm::Inputs::Base
  def input(wrapper_options)
    currency = options.delete(:currency) || default_currency
    merged_input_options = merge_wrapper_options(input_html_options, wrapper_options)

    content_tag(:div, input_group(currency, merged_input_options), class: "input-group")
  end

  private

  def input_group(currency, merged_input_options)
    "#{currency_addon(currency)} #{@builder.text_field(attribute_name, merged_input_options)}".html_safe
  end

  def currency_addon(currency)
    content_tag(:span, currency, class: "input-group-addon")
  end

  def default_currency
    "$"
  end
end

Now, all I have to do in my form is call:

<%%= f.input :registration_fee, as: :currency, currency: "€" %>