Rails has_many chain - ruby-on-rails

Question

So I have a table structure below:
Plane
plane_id
plane_info
Seating
seating_id
seating_info
PlaneSeating
plane_seating_id
plane_id
seating_id
PlaneSeatingNote
plane_seating_note_id
plane_seating_id
note_id
Note
note_id
note_info
This gives me a third-normal DB, but I need to set the model relations up.
I currently have:
class Plane < ActiveRecord::Base
has_many :plane_seatings, dependent: :destroy
has_many :seatings, through: :plane_seatings
end
class Seatings < ActiveRecord::Base
has_many :plane_seatings, dependent: :destroy
has_many :planes, through: :plane_seatings
end
class PlaneSeating < ActiveRecord::Base
belongs_to :plane
belongs_to :seating
has_many :plane_seating_notes, dependent: :destroy
has_many :notes, through: :plane_seating_notes
end
class PlaneSeatingNote < ActiveRecord::Base
belongs_to :plane_seating
has_one :note
end
class Note < ActiveRecord::Base
end
Now, this will give me the ability to say Plane.all.first.plan_seatings.first.notes and get the notes I believe. However, I'd like to be able to say Plane.all.first.seatings.notes and get the notes associated with that plane given that seating.
My thought is there should be a way to say, in Plane:
has_many :seatings, through: plane_seating, has_many :notes, through: plane_seating
or some other chaining magic to get a seating with some notes that only apply to that plane and seating combo. a :with, if you will. But I can't think of any syntax that would give me that. Anyone know?

Answer 1

The best is to pivot it the other way, it you want to grab the notes for a certain Plane:
Note.joins(plane_seating_note: [:plane_seating]).where(plane_seating_note: {plane_seating: {plane_id: 1})
You could make that a scope if you're using it in multiple places and if you want it on the Plane model:
class Plane < ActiveRecord::Base
has_many :plane_seatings, dependent: :destroy
has_many :seatings, through: :plane_seatings
def notes
#notes ||= Note.for_plane_id id
end
end
class Note < ActiveRecord::Base
has_many :plane_seating_notes
scope :for_plane_id ->(plane_id) { joins(plane_seating_notes: [:plane_seating]).where(plane_seating_notes: {plane_seating: {plane_id: plane_id}) }
end
For a specific seat on a specific plane, you'd typically see something like this in a controller:
#seat = PlaneSeat.find params[:id]
#plane = #seat.plane
#notes = Note.joins(:plane_seating_notes).where(plane_seating_notes: {plane_seating_id: #seat.id})
But since you have a HMT you could just do
#seat = PlaneSeat.find params[:id]
#plane = #seat.plane
#notes = #seat.notes
A couple "Rails-way" notes:
Unless you are using Note elsewhere, you should just skip the plane_seat_notes.
Consider using has_and_belongs_to_many if you aren't appending any extra meta-data in the intermediate table; this makes relationships easier and gives you shallower query helpers
Consider using polymorphic relationships rather than unnecessary join tables

Answer 2

I used a helper method in the Plane model to get what I wanted. This method may be inefficient if you are dealing with large datasets, but for my datasets, it works fine. It packages up each seating subset for each plane with the notes associated with it into a hash.
#Get an easy to read hash of the seatings with their notes
def seatings_with_notes
#seatings_with_notes = []
self.plane_seatings.each do |item|
seating = Seating.where(id: item.product_application_id).first
notes = item.notes
combo = {seating:seating, notes:notes}
#seatings_with_notes.append(combo)
end
return #seatings_with_notes
end