Rails Multiple Parent Relationships - ruby-on-rails

Question

Three models:
User
List
Item
A User can have many Lists and a List can have many Items. Each List can have an Item added to it by ANY User. This means, for example, that you can create a list and I can add items to it. Make sense? Let's keep going.
I want to be able to find all Items created by X User at any point in time.
class User < ActiveRecord::Base
has_many :lists
has_many :items
end
class List < ActiveRecord::Base
belongs_to :user
has_many :items
end
class Item < ActiveRecord::Base
belongs_to :list
belongs_to :user
end
I don't like this. It has a funky smell but I can't put my finger on it. I feel like there should be something better. When creating a new Item I would have to write something that looks like the following:
list = List.find(params[:list_id])
#item = list.items.new(params[:item])
user = User.first
#item.user = user
#item.save!
So, what am I missing? Are my relationships wrong (very likely)? Tell me! :)

Answer 1

It seems like there can be two different relationships between items and users: 1) items are added to lists by users, and 2) lists are created by users.
Only one user can create a list. Many users can add items to lists after they are created.
So modeling this requires two different relationships
class User < ActiveRecord::Base
has_many :lists
has_many :items_added, :class_name => "Item", :foreign_key => "added_by_user_id"
end
class List < ActiveRecord::Base
belongs_to :user
has_many :items
end
class Item < ActiveRecord::Base
belongs_to :list
belongs_to :added_by_user, :class_name => "User", :foreign_key => "user_id"
end
It makes sense to assume that you all these relationships are required -- that is, a list needs a user_id when it's created to show who created it. Likewise, an item needs to record who added it to the list.
You'd need to add the added_by_user_id column to your items table to make this work and keep track of which user added the item.
So you could do this:
# To create a user and a list is easy!
user = User.create(user_params)
list = user.create_list(list_params)
# but when adding an item, you need to know which user is adding it
item = list.create_item({:added_by_user => current_user, :item_name => 'name', etc})
Now you can find all items added by a user using:
all_user_items = user.items_added
I haven't tested this and it's a bit complicated so I may have 1-2 mistakes in the code, but generally that's one way this could be modeled.