STI or Polymorphic collection for Project images

This code was presented as a working solution in a discussion about using polymorphic associations.

In this case a simple STI or polymorphic collection of images in Project seems to be more appropriate at first glance, but that may not fit the developer's requirement in this case.

Implementation as implied by problem discussion

class Image < ApplicationRecord
  belongs_to :imageable, polymorphic: true
end

class ImageOne < ApplicationRecord
  belongs_to :project
  has_many :images, as: :imageable
end

class ImageTwo < ApplicationRecord
  belongs_to :project
  has_many :images, as: :imageable
end

class Project < ApplicationRecord
  has_one :image_one
  has_one :image_two
end

Exercise in Rails console

$ bin/rails c
Loading development environment (Rails 7.0.0.alpha2)
irb(main):001:0> Project.create(name: "test")
irb(main):002:0> ImageOne.create(project: Project.first)
irb(main):002:0> ImageTwo.create(project: Project.first)
irb(main):005:0> ImageOne.first.images.create(url: "/images/test1")
irb(main):006:0> ImageTwo.first.images.create(url: "/images/test1")
irb(main):012:0> ImageTwo.first.project
irb(main):013:0> ImageTwo.first.project.image_one

Creating the app

** Performed on Linux Ubuntu 20.04 LTS

Install Rails 7 if needed

rails_ver=`rails -v | cut -d ' ' -f 2`
rails_7_ver='7.0.0.alpha2'

if [ "$rails_ver" = "$rails_7_ver" ]
then
    echo "Rails $rails_7_ver already installed, yay!"
else    
    echo "Installing Rails version $rails_7_ver"
    gem install rails -v $rails_7_ver
fi

Create a Rails 7 app (with tailwind, esbuild and postgresql)

rails new project_images -j esbuild --css tailwind --database postgresql

Generate the models

$ cd project_images
$ bin/rails g model Project name:string 
$ bin/rails g model Image url:string imageable_type:string imageable_id:integer
$ bin/rails g model ImageOne project:references
$ bin/rails g model ImageTwo project:references

manual Model Edits

app/project.rb

class Project < ApplicationRecord
  # added manually
  has_one :image_one
  has_one :image_two
end

app/image.rb

class Image < ApplicationRecord
  # added manually
  belongs_to :imageable, polymorphic: true
end

app/image_one.rb

class ImageOne < ApplicationRecord
  belongs_to :project
  
  # added manually  
  has_many :images, as: :imageable
end

app/image_two.rb

class ImageOne < ApplicationRecord
  belongs_to :project

  # added manually
  has_many :images, as: :imageable
end

rlogwood/rails_discuss-project_images