How to constrain db elements in rails?

Question

I have four tables in my db Movie, Showing, Ticket and Purchase. A Movie has many Showings, a Showing has many Tickets and a Purchase has many Tickets.

I'd like to constrain it so that all the Tickets in the Purchase can only be for exactly one Movie. I'm new to Rails and wondered if there was a way to do this in the Model. (validate or something similar)

bratsche · Accepted Answer · 2013-07-22 04:55:10Z

1

class Purchase
  validate :validate_same_movie

  private

  def validate_same_movie
    movie_ids = tickets.map do |ticket|
      ticket.showing.movie.id
    end.uniq

    errors[:base] << "Can't have more than one movie in a purchase." if movie_ids.length > 1
  end
end

Something along these lines.

But I would also urge you to think about exactly why you're introducing this additional complexity into your system. In my experience, I typically buy movie tickets for the same movie at once and I don't recall when I've bought tickets for different movies in a single purchase. But just because I haven't done it doesn't mean nobody does. You're adding complexity and you're reducing functionality of your site. I'm not saying you don't have a valid reason, because I don't know what your app is.. but just a suggestion that you might think about if you really need this.

answered Jul 22, 2013 at 4:55

bratsche

2,66421 silver badges24 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

calico-cat Over a year ago

Thank you. It's not really movies and tickets, but the domain-specific terminology would detract.

bratsche Over a year ago

Oh, well in that case ignore my second paragraph. :) Hope the validate code helps you out.

t56k · Accepted Answer · 2013-07-22 02:09:32Z

0

What about something like this?

class Purchase < ActiveRecord::Base
  has_one :movie
  has_many :tickets
end

class Ticket < ActiveRecord::Base
  has_one :purchase
end

class Movie < ActiveRecord::Base
  has_many :purchases
end

answered Jul 22, 2013 at 2:09

t56k

7,03110 gold badges59 silver badges122 bronze badges

1 Comment

calico-cat Over a year ago

I don't wish to change the design to add a relationship between Movie and Purchase, I just want to constrain that Purchase must include Tickets for only one Movie.

Collectives™ on Stack Overflow

How to constrain db elements in rails?

2 Answers 2

2 Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related