rails has_many :through has_many :through

Question

I'm wondering to what extent I can use associations in Rails. Take into consideration the following:

class User < ActiveRecord::Base
    has_one :provider
    has_many :businesses, :through => :provider
end

class Provider < ActiveRecord::Base
    has_many :businesses
    has_many :bids, :through => :businesses
    belongs_to :user
end

class Business < ActiveRecord::Base
    has_many :bids
    belongs_to :provider
end

class Bid < ActiveRecord::Base
    belongs_to :business
end

I am able to set up these nifty shortcuts like User.businesses and Provider.bids but what about doing something like User.bids? Is it possible to associate an association, so to speak?

Answer 1

This is entirely possible, but needs a little extra work. The following model definitions used in conjunction with the nested_has_many plugin you can fetch all bids belonging to a user with just @user.bids

class User < ActiveRecord::Base
    has_one :provider
    has_many :businesses, :through => :provider
    has_many :bids, :through => :businesses
end

class Provider < ActiveRecord::Base
    has_many :businesses
    has_many :bids, :through => :businesses
    belongs_to :user
end

class Business < ActiveRecord::Base
    has_many :bids
    belongs_to :provider
end

class Bid < ActiveRecord::Base
    belongs_to :business
end

However getting a user from a bid will take a more work.

Answer 2

If you just want to fetch the records, why not use use #delegate? It works just fine, at least in the scenario you've described.

class User < ActiveRecord::Base
    has_one :provider
    delegate :bids, :to => :provider
end

class Provider < ActiveRecord::Base
    has_many :businesses
    has_many :bids, :through => :businesses
    belongs_to :user
end

class Business < ActiveRecord::Base
    has_many :bids
    belongs_to :provider
end

class Bid < ActiveRecord::Base
    belongs_to :business
end

Although in my not-so-humble-opinion you should just chain the methods because it's more straightforward, and you're no longer achieving the performance boost unless you go with some crazy custom SQL as tadman says.