# Unique entries **URL:** \ **Category:** Rails\ **Created:** [October 11, 2007, 10:49pm UTC](https://www.ruby-forum.com/t/unique-entries/116996 "2007-10-11T22:49:10Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![snantz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c2a13f/32.png) [@snantz](https://www.ruby-forum.com/u/snantz)\ **Post date:** [October 11, 2007, 10:49pm UTC](https://www.ruby-forum.com/t/unique-entries/116996/1 "2007-10-11T22:49:10Z")
I have this table associating airlines with rental cars. It has four columns - user\_id, airline\_id, rentalcar\_id and id. I need to make sure that the combo of airline\_id and rentalcar\_id is always unique - in other words, a user cannot have two fields with the same airline\_id and rentalcar\_id. Is this done with one of the validation commands in the model? I have look at the one that I can find and none seems to fit all that well. Thanks, -S ---
**Author:** ![snantz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c2a13f/32.png) [@snantz](https://www.ruby-forum.com/u/snantz)\ **Post date:** [October 11, 2007, 11:03pm UTC](https://www.ruby-forum.com/t/unique-entries/116996/2 "2007-10-11T23:03:37Z")
> I have this table associating airlines with rental cars. It has four > columns - user\_id, airline\_id, rentalcar\_id and id. I need to make sure > that the combo of airline\_id and rentalcar\_id is always unique - in > other words, a user cannot have two fields with the same airline\_id and > rentalcar\_id. Is this done with one of the validation commands in the > model? I have look at the one that I can find and none seems to fit all > that well. Thanks, Create a unique index on user\_id, airline\_id, rentalcar\_id in your migration… that would be one way ---
**Author:** ![snantz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c2a13f/32.png) [@snantz](https://www.ruby-forum.com/u/snantz)\ **Post date:** [October 11, 2007, 11:37pm UTC](https://www.ruby-forum.com/t/unique-entries/116996/3 "2007-10-11T23:37:36Z")
You could try: validates\_uniqueness\_of :rentalcar\_id, :scope =\> :airline\_id Whichever is the widest scope (e.g., can an airline have a lot of rental cars? Or the other way around?) should probably go with :scope. I don’t _think_ it would affect anything, but for modeling’s sake it should be that way. 🙂 –Jeremy On 10/11/07, Shandy N. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > – > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). > > > – [http://www.jeremymcanally.com/](http://www.jeremymcanally.com/) My books: Ruby in Practice > **[Ruby in Practice](https://www.manning.com/books/ruby-in-practice)** > > Like Ruby itself, Ruby in Practice will make you more productive. The book shows you practical techniques and strategies for small projects and large-scale environments. A cookbook-style reference, it gives you concrete examples of systems... My free Ruby e-book > **[Site not found · DreamHost](http://www.humblelittlerubybook.com/)** > > The owner of this domain has not yet uploaded their website. My blogs: > **[Site not found · DreamHost](http://www.mrneighborly.com/)** > > The owner of this domain has not yet uploaded their website. [http://www.rubyinpractice.com/](http://www.rubyinpractice.com/) ---
**Author:** ![snantz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c2a13f/32.png) [@snantz](https://www.ruby-forum.com/u/snantz)\ **Post date:** [October 12, 2007, 5:29pm UTC](https://www.ruby-forum.com/t/unique-entries/116996/4 "2007-10-12T17:29:17Z")
removed\_email\_address@domain.invalid wrote: > I second that. I’m using validates\_uniquemess\_of with :scope for the > same purpose in one of my projects. In the testing I have done it did > not matter which one went in the :scope. I agree that the widest > would be the better choice for readability later. > > On Oct 11, 5:36 pm, “Jeremy McAnally” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) What I was trying to do was to have a user with an airline membership be associated to as many rental car companies as they desired, but to insure the integrity of the database, I didn’t want an entry that had all three columns the same - user\_id, airline\_id, and rentalcar\_id. The same user\_id and airline\_id was ok as long as they all had different rentalcar\_id’s. Hope this makes some sense, because it was confusing the hell out of me. Anyway, here is what I did: validates\_uniqueness\_of :rentalcar\_id, :scope =\> :airline\_id and :\_user\_id and it seems to work. I didn’t know that I could say and but apperently I can. Thanks all, -S ---
**Author:** ![snantz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c2a13f/32.png) [@snantz](https://www.ruby-forum.com/u/snantz)\ **Post date:** [October 12, 2007, 6:40pm UTC](https://www.ruby-forum.com/t/unique-entries/116996/5 "2007-10-12T18:40:22Z")
On 10/12/07, Shandy N. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > validates\_uniqueness\_of :rentalcar\_id, :scope =\> :airline\_id and > :\_user\_id > > and it seems to work. I didn’t know that I could say and but apperently > I can. Thanks all, Well, you can “say” it, but Ruby will parse that as: validates\_uniqueness\_of(:rentalcar\_id, :scope =\> :airline\_id) and :\_user\_id The “and” part is a no-op, which I’m guessing isn’t what you intend. If you want to use two columns for the scope, the syntax is: :scope =\> [:airline\_id, :user\_id] which is illustrated in the API docs for validates\_uniqueness\_of ---
**Author:** ![snantz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c2a13f/32.png) [@snantz](https://www.ruby-forum.com/u/snantz)\ **Post date:** [October 12, 2007, 4:24pm UTC](https://www.ruby-forum.com/t/unique-entries/116996/6 "2007-10-12T16:24:50Z")
I second that. I’m using validates\_uniquemess\_of with :scope for the same purpose in one of my projects. In the testing I have done it did not matter which one went in the :scope. I agree that the widest would be the better choice for readability later. On Oct 11, 5:36 pm, “Jeremy McAnally” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)