multiple has_many through relationships

Question

I'm setting up a collaborative writing platform. A user can have sets of items where any item can be in any set and belong to any user. This leads to a few problems though.

These are my model relationships:

class Association < ActiveRecord::Base
  belongs_to :user
  belongs_to :set
  belongs_to :item
end  

class Set < ActiveRecord::Base
  has_many :associations
  has_many :users, through: :associations
  has_many :items, through: :associations 
end

class Item < ActiveRecord::Base
  has_many :associations
  has_many :users, through: :associations
  has_many :sets, through: :associations 
end

I can't figure out the "rails way" of handling this correctly.

Problem 1:

When creating a new item, only the set/item association is stored and not the user:

class ItemsController < ApplicationController
  def create
    @set = current_user.sets.find(params[:set_id])
    @set.where(title: params[:item][:title]).first_or_create!
  end
end   

*UPDATE*

To fix problem 1, the best I could figure out was to do the following:

@set  = current_user.sets.find(params[:set_id])
@item = Item.where(name: params[:item][:title]).first_or_create!
Association.where(item_id: @item.id, set_id: @set.id, user_id: current_user.id).first_or_create!

Feels very wrong though!

Problem 2:

Assuming the associations table is populated correctly from problem 1, the following controller will return all items owned by the set but disregard user ownership:

class SetsController < ApplicationController
  def index
    @sets = current_user.sets.includes(:items)
  end
end 

*UPDATE*

Still no luck finding an answer on this. To explain the problem a bit better:

The following will return only sets that belong to the current user

@sets = current_user.sets.all

However, the following will return only the user's sets but will include ALL of the items for the sets even if they don't belong to the current user. In other words, the user scope is dropped.

@sets = current_user.sets.includes(:items)

I've been trying to solve this all day and can't seem to find a lead

Answer 1

Your first problem is making sure your instance variable is the same. One is capitalized. Should look like this:

class ItemsController < ApplicationController
  def create
    @set = current_user.sets.find(params[:set_id])
    @set.where(title: params[:item][:title]).first_or_create!
  end
end    

Answer 2

Is this what you mean? A user can have many items. A user can have many sets.

An item can belong to multiple users. An item can belong to multiple sets.

If that's the case, you need more than one join model.

Class UserItemAssociation < ActiveRecord::Base
  belongs_to :user
  belongs_to :item
end

Class SetItemAssociation < ActiveRecord::Base
  belongs_to :set
  belongs_to :item
end

Class Item < ActiveRecord::Base
  has_many :user_item_associations
  has_many :users, through: :user_item_associations

  has_many :set_item_associations
  has_many :sets, through :set_item_associations
end

Class Set < ActiveRecord::Base
  belongs_to :user
end

In the controller:

@set = current_user.sets.find_or_create_by(params[:set_id])
@item = @set.items.where(title: params[:item][:title]).first_or_create!
current_user.items << @item

However, here's a different way of looking at it.

In the user model, add this method.

  def items
    self.sets.collect{|set| set.items}.flatten
  end

This way, you only need the Association model to join the users with sets, but you can still access the user.items now.