vl3

Building Rich Domain Models in Rails

Abstract

Domain model is an effective tool for software development. It can be used to express really complex business logic, and to verify and validate the understanding of the domain among stakeholders. Building rich domain models in Rails is hard. Primarily, because of Active Record, which doesn't play well with the domain model approach.

One way to deal with this problem is to use an ORM implementing the data mapper pattern. Unfortunately, there is no production ready ORM doing that for Ruby. DataMapper 2 is going to be the first one.

Another way is to use Active Record just as a persistence mechanism and build a rich domain model on top of it. That's what I'm going to talk about here.

vl3

#!/bin/sh

# Credits: http://stackoverflow.com/a/750191

git filter-branch -f --env-filter "
    GIT_AUTHOR_NAME='Newname'
    GIT_AUTHOR_EMAIL='new@email'
    GIT_COMMITTER_NAME='Newname'
    GIT_COMMITTER_EMAIL='new@email'
  " HEAD

vl3

class FeatureToggle(object):
    def __init__(self, old, new, toggle):
        self.old = old
        self.new = new
        self.toggle = toggle

    def __getattr__(self, name):
        def wrapper(*args, **kwargs):
            instance_to_use = self.new if self.toggle else self.old
            return getattr(instance_to_use, name)(*args, **kwargs)

vl3

def flatten ary
  flattenized_ary = []
  ary.each do |element|
    if element.class == Array
      flattenized_ary += flatten(element)
    else
      flattenized_ary << element
    end
  end
  flattenized_ary

vl3

ActiveAdmin.register Band do
  permit_params :name, :description, artists_attributes: [:id]
  

  # nested form to edit and new
  form do |f|
    f.inputs "Band" do
      f.input :name
      f.input :description
      f.input :artists, :as => :select, :input_html => { :multiple => true }