# How do you allow users make custom shopping lists? **URL:** \ **Category:** Rails\ **Created:** [February 27, 2010, 7:22am UTC](https://www.ruby-forum.com/t/how-do-you-allow-users-make-custom-shopping-lists/184252 "2010-02-27T07:22:33Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![The\_programmer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/22d042/32.png) [@The\_programmer](https://www.ruby-forum.com/u/The_programmer)\ **Post date:** [February 27, 2010, 7:22am UTC](https://www.ruby-forum.com/t/how-do-you-allow-users-make-custom-shopping-lists/184252/1 "2010-02-27T07:22:33Z")
Hi, I asked Ryan bates, the owner of [railscasts.com](http://railscasts.com) if he knew of any documentation that would explain what code to use to allow users make their own lists in RoR. He referred me to here. I’m trying to make it so user A can make a shopping list and populate it with items like eggs, fruit, oatmeal, etc. I know that I could easily make one shopping list for all users to use but my situation is different. I want user A to be able to make a list for different types of food and such. The problem is, I don’t know if this is possible or how to do it without other users seeing their shopping list. I’m very adamant on letting users make their own shopping lists so any info on how to do that is very much appreciated. ---
**Author:** ![The\_programmer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/22d042/32.png) [@The\_programmer](https://www.ruby-forum.com/u/The_programmer)\ **Post date:** [February 27, 2010, 9:37am UTC](https://www.ruby-forum.com/t/how-do-you-allow-users-make-custom-shopping-lists/184252/2 "2010-02-27T09:37:44Z")
I’d start by creating various models to represent the user, the lists, the items _in_ the lists, and a pairing relationship between them (aka a “join table”, or in Rails lingo, a “has many through” relationship). For example, you could have 4 models: User ShoppingList Food Foodable (the join model) User has all the standard fields you need for a user with authentication, etc. To handle authentication, do a Google search for “authlogic” and do some reading on it. ShoppingList consists only of: user\_id name (You could also add “notes” or something to that effect here too, if you wanted.) Finally, Food would simply be: name …that’s it. So now you have: ## User: id username email …etc… ## ShoppingList id user\_id name ## Food id name ## Foodable (the join model between foods and shopping lists) id shopping\_list\_id food\_id So you can see how, using foreign keys, we can link any number of foods to multiple shopping lists without duplicating information in the database. For example, if we had a food called “T-Bone Steak”, it only needs to be listed in the database ONCE. Not hundreds of times. Then, in the Foodable join table, we link its unique ID in the food table (say that ID is 199) to every list in which it appears. By linking the shopping list model directly to the user model (so shopping\_list belongs\_to :user), we ensure that any single shopping list belongs to ONLY one user at any given time, meaning that your database select query (or a “find” on that model) will only return the lists that specific user owns, never anyone else’s, making it all but impossible that user A would see user B’s list. This is basically a data architecture/database normalization problem. I suggest looking up the basics of how ActiveRecord works, especially model relationships such as belongs\_to and has\_many with the :through option (you could also do a has\_and\_belongs\_to\_many, but I hear that practice is falling out of favor these days because the has\_many :through allows you to work directly with the join model and does the same thing.) You were on the right track checking out Railscasts - Ryan does a great job of breaking down complex topics to make them easy to understand. I suggest you look through it a bit more to learn more about how ActiveRecord works. In addition, check out Rails Guides: > **[Getting Started with Rails — Ruby on Rails Guides](https://guides.rubyonrails.org/getting_started.html)** > > Getting Started with RailsThis guide covers getting up and running with Ruby on Rails.After reading this guide, you will know: How to install Rails, create a new Rails application, and connect your application to a database. The general layout of a... - Will help make sure you have the foundational knowledge you need to get started [Active Record Associations — Ruby on Rails Guides](http://guides.rubyonrails.org/association_basics.html) - Explains ActiveRecord associations like has\_many, belongs\_to, has\_many :through, etc. Good luck.