ChoicesFields: model macro to define helper functions on AR model attributes that have pre-determined values

choices_fields.rb

module ChoicesFields
  extend ActiveSupport::Concern

  module ClassMethods
    # Class macro that defines useful function for choice fields (<option> tag fields).
    #
    # Will define:
    #   ::fieldname_choices_hash
    #     Returns the hash given to the `choices_field` macro function.
    #
    #   ::fieldname_choices
    #     Returns the "machine" values, used primarily for AR validation with:
    #       validates :a_field, inclusion: { within: self.a_field_choices }
    #     WARNING: Use `choice_field` before `validates` in your AR model definition.
    #     TODO: Add a convenient custom validator that reads the *_choices automatically.
    #
    #   ::fieldname_options
    #     Returns an array of arrays, ordered to use with `select_tag` or `f.select`.
    #
    #   #fieldname_humanized
    #     Will read `#fieldname` and return the associated human-redable value.
    #
    # See engines/business/spec/models/concern_choices_fields_spec.rb for details.
    #
    def choices_field(fieldname, choices_hash)
      fieldname = fieldname.to_sym
      fieldname_choices_hash = "#{fieldname}_choices_hash".to_sym
      fieldname_choices = "#{fieldname}_choices".to_sym
      fieldname_options = "#{fieldname}_options".to_sym
      fieldname_humanized = "#{fieldname}_humanized".to_sym

      choices_hash = choices_hash.with_indifferent_access
      choices_keys = choices_hash.keys
      choices_select = choices_hash.to_a.map(&:reverse)

      ## Class Methods ##
      # Hash defining choices: machine => human_readable
      define_singleton_method fieldname_choices_hash do
        choices_hash
      end
      # Choices for validation
      define_singleton_method fieldname_choices do
        choices_keys
      end
      # Options for select
      define_singleton_method fieldname_options do
        choices_select
      end
      ## Instance Methods ##
      # Humanized name of current field
      define_method fieldname_humanized do
        choices_hash[self.send(fieldname)]
      end
    end
  end
end

concern_choices_fields_spec.rb

RSpec.describe ChoicesFields do
  before :example do
    class C
      attr_accessor :a_field

      include Business::Concerns::ChoicesFields

      choices_field :a_field, {
        'hello' => "Hello",
        'world' => "World",
      }
    end

    @it = C.new
  end

  it "defines correctly Class method ::fieldname_choices_hash" do
    expect(@it.class.a_field_choices_hash).to eq({
      'hello' => "Hello",
      'world' => "World",
    })
  end

  it "defines correctly Class method ::fieldname_choices" do
    expect(@it.class.a_field_choices).to eq(['hello', 'world'])
  end

  it "defines correctly Class method ::fieldname_options" do
    expect(@it.class.a_field_options).to eq([
      ["Hello", 'hello'],
      ["World", 'world'],
    ])
  end

  it "defines correctly Instance method #fieldname_humanized" do
    @it.a_field = 'hello'
    expect(@it.a_field_humanized).to eq("Hello")
  end

end