What is the best way to setup my tables and relationships for this use case?

Answer 1

I believe you should use the following:

class User < ActiveRecord::Base
   has_and_belongs_to_many :causes
   has_and_belongs_to_many :campaigns
end

class Cause < ActiveRecord::Base
   has_and_belongs_to_many :users
   has_many :campaigns
end

class Campaign < ActiveRecord::Base
   has_and_belongs_to_many :users
   belongs_to :cause
end

This way you can use

User.causes
User.campaigns

Cause.campaing
Cause.users

Campaign.users
Campaign.cause

You can read here about has_and_belongs_to_many relationship, here about has_one and here about belongs_to.

Let me know if this is what you want :]

Edit:

"I would still need User.campaigns to be campaigns from a user's causes or individual campaigns associated with a user"

You can have a method on users model that returns all campaigns. Something like this:

def all_campaigns
   self.campaigns + self.causes.collect{ |c| c.campaigns }
end

Answer 2

This should work.

class User < ActiveRecord::Base
  has_many :causes, :through => :cause_users
  has_many :campaigns, :through => :campaign_users
  # other model stuff

class Cause < ActiveRecord::Base
  has_many :users, :through => :cause_users
  has-many :campaigns
  # other model stuff

class Campaign < ActiveRecord::Base
  belongs_to :cause
  has_many :users, :through => :campaign_users
  # other model stuff

class CampaignUser < ActiveRecord::Base
  belongs_to :campaign
  belongs_to :user
  # other model stuff

class CauseUser < ActiveRecord::Base
  belongs_to :cause
  belongs_to :user
  # other model stuff

has_many :through requires that you create a new model for each of these joins: campaign_users and cause_users, as is shown but it provides more functionality later on than has_and_belongs_to_many.

I would also suggest using better names than :campaign_users and :cause_users so the relationship is more meaningful.

Answer 3

You can make :has_many :through associations between users and campaigns using a join model, and also between users and causes using the another join model. The you can make a :has_many :campaigns association in the causes model, putting a :belongs_to :cause in the campaign model.

But you won't be able to fetch all the users campaigns or causes by User.campaigns.orders or User.order.campaigns. You should make an iteration over the User.campaigns collection or User.causes, fetching Campaign.cause or Cause.capaigns. Or even making a custom SQL query, using joins and conditions to filter information in the joins.