Rails - Do I need a join table for this or column on each model?

Question

I'm building an app where there will be tours with reservations. Each tour will be available on different days and each reservation will belong to a single day. My question is, should I create a "day" column on each model I want to use it on (tour and reservation) or should I create some kind of association and/or join table, like below?

I'm just not sure which one would be more appropriate. My goal is to add a set of days for each tour, then display those days on the reservations page and allow users to choose a day.

Models
reservations
tours
days
days_tours (join table)

Associations
tour has_many :days_tours
tour has_many :days, through: :days_tours
day has_many :days_tours
day has_many :tours, through: :days_tours
reservation has_one :day

Answer 1

I would use a Reservations table with three foreign keys: user_id, tour_id, and day_id.

Then that table could serve as a join table.

Then you could set up the following, depending on your needs:

# User
  has_many :reservations
  has_many :tours, through: :reservations
  has_many :days, through: :reservations

# Tour
  has_many :reservations
  has_many :days, through: :reservations
  has_many :users, through: :reservations

# Day
  has_many :reservations
  has_many :users, through: :reservations
  has_many :tours, through: :reservations

Also, remember every has_many or has_one on one side needs a belongs_to on the other side.

# Reservation
  belongs_to :user
  belongs_to :tour
  belongs_to :day

As for has_and_belongs_to_many -- it's often simpler to set up, but it's far less flexible than has_many :through, especially if you're joining more than two models.