# Validates\_presence\_of \*\_id attributes **URL:** \ **Category:** Rails\ **Created:** [January 3, 2006, 8:34am UTC](https://www.ruby-forum.com/t/validates-presence-of-id-attributes/56098 "2006-01-03T08:34:58Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![John\_I](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/74df32/32.png) [@John\_I](https://www.ruby-forum.com/u/John_I)\ **Post date:** [January 3, 2006, 8:34am UTC](https://www.ruby-forum.com/t/validates-presence-of-id-attributes/56098/1 "2006-01-03T08:34:58Z")
Hi all, I am a newbie to Rails. Please enlighten me on how to do this appropriately, the Rails and the Ruby way: Suppose I have a Recipe model. Let’s simplify things and pretend that it has only 2 attributes, a :name and the other is a ‘category\_id’. In the recipes table, category\_id is a foreign key to field id of table categories. We also assume that I have generate the appropriate scaffolding code for Recipe and Category. All goes well if I go to [http://localhost:3000/categories](http://localhost:3000/categories) (I’m using WEBrick) and add a new Category and then go to [http://localhost:3000/recipes](http://localhost:3000/recipes) and add a Recipe and choose a category for the recipe. What if I go to [http://localhost:3000/recipes](http://localhost:3000/recipes) first and add a new recipe without specifying a category (note that I enforce the category\_id field in the recipes table to be not null). Rails will definitely complain. Is there somekind of “validates\_presence\_of” for \*\_id kinds of field thus the user of my application can be notified to make a category first before adding recipe? Tq very much, John ---
**Author:** ![John\_I](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/74df32/32.png) [@John\_I](https://www.ruby-forum.com/u/John_I)\ **Post date:** [January 3, 2006, 8:59am UTC](https://www.ruby-forum.com/t/validates-presence-of-id-attributes/56098/2 "2006-01-03T08:59:36Z")
John, Check out ‘validates\_associated’ [http://api.rubyonrails.com/classes/ActiveRecord/Validations/](http://api.rubyonrails.com/classes/ActiveRecord/Validations/) ClassMethods.html#M000689 Chris Nolan.ca [http://kweschun.com/](http://kweschun.com/) - Do you have a kweschun? ---
**Author:** ![John\_I](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/74df32/32.png) [@John\_I](https://www.ruby-forum.com/u/John_I)\ **Post date:** [January 3, 2006, 12:13pm UTC](https://www.ruby-forum.com/t/validates-presence-of-id-attributes/56098/3 "2006-01-03T12:13:32Z")
On 1/3/06, Chris Nolan.ca [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > John, > Check out ‘validates\_associated’ > Chris Nolan.ca Hey, thanks for the response. Thanks for introducing me to validates\_associated too. However, after updating my Recipe model with: validates\_associated :category , the error is still there. I’m afraid that this doesn’t have anything to do with validating association, here’s the error: “You have a nil object when you didn’t expect it! You might have expected an instance of Array. The error occured while evaluating nil.inject” I think this is because I use \<%= collection\_select ‘recipe’, ‘category\_id’, @categories, ‘id’, ‘description’ %\> in \_form.rhtml and by the time I intentionally create a new recipe, there is not even a single category. How to handle this the Rails way? Tq. ---
**Author:** ![John\_I](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/74df32/32.png) [@John\_I](https://www.ruby-forum.com/u/John_I)\ **Post date:** [January 3, 2006, 1:39pm UTC](https://www.ruby-forum.com/t/validates-presence-of-id-attributes/56098/4 "2006-01-03T13:39:09Z")
in your Recipe model, you just do: validates\_presence\_of :name, :category\_id now as far as “before” adding a recipe, the app isn’t going to know you haven’t selected anything until you submit the form, then your app will do the validation before the save. if the validation fails, you can have your app notify the user using something like: \<%= error\_messages\_for(:recipe) %\> in your “New Recipe” view. of course, you could always use javascript to validate your form before you submit it. now if your problem is that there are no pre-existing categories, you might want to think about adding a few default to the app or allow the user to create a new category when they are creating a new recipe. if a category is nothing more than a name like “Dessert” or whatever, just add \<%= text\_field\_tag “new\_category\_name”, “” %\> in your create/edit form view and in your create/update controller methods, do a check on this field…if the user entered a new category, create that category then use it to create the recipe. ---
**Author:** ![John\_I](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/74df32/32.png) [@John\_I](https://www.ruby-forum.com/u/John_I)\ **Post date:** [January 3, 2006, 7:28pm UTC](https://www.ruby-forum.com/t/validates-presence-of-id-attributes/56098/5 "2006-01-03T19:28:24Z")
Chris H. wrote: > in your Recipe model, you just do: > > validates\_presence\_of :name, :category\_id Actually, I suggest you use validates\_presence\_of :category Because the category association will use the category\_id column to try and get the Category object, you’ll end up checking if the category\_id is not nil and if it is not nil, it’ll also try to load the associated row from the Category table. If that row doesn’t exist for the category\_id, then you’ll also get a validation error. So you get two checks for one line of code. Regards, Blair – Blair Z., Ph.D. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) Subversion and Orca training and consulting [http://www.orcaware.com/svn/](http://www.orcaware.com/svn/)