gistfile1.txt

Create an app:

    rails new whatever

Generate some scaffolding:

    rails generate scaffold User name:string
    rails generate scaffold Item user_id:integer collection_id:integer name:string
    rails generate scaffold Collection user_id:integer name:string

Migrate

    rake db:migrate
    
Edit the model files for each. Make them look like this:

    class CollectionsController < ApplicationController
      belongs_to :user
      has_many :items
    end

    class ItemsController < ApplicationController
      belongs_to :user
      has_and_belongs_to_many :collections
    end

    class UsersController < ApplicationController
      has_many :items
      has_many :collections
    end

Now you can start your server:

    rails s

And then you can create some records via these URLs. For now, a good demo is to create one user, some items, and a collection. Or do more.

    localhost:3000/users
    localhost:3000/items
    localhost:3000/collections

Once you've done that, open up console:

    rails c

And now you can do stuff like:

    User.first                    # shows the first User
    User.first.items              # shows the first User's items
    User.first.items.first.name   # shows the first User's first item's name
    
    Item.first                    # etc
    Item.first.user
    Item.first.user.name
    
    Collection.first          
    Collection.first.user     
    Collection.first.user.name