# Complex forms: only one level of “arrayn ess” is allowed? **URL:** \ **Category:** Rails\ **Created:** [April 15, 2009, 9:39am UTC](https://www.ruby-forum.com/t/complex-forms-only-one-level-of-a-oearrayn-essa-is-allowed/165558 "2009-04-15T09:39:01Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![PJPJPJ](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/6bbea6/32.png) [@PJPJPJ](https://www.ruby-forum.com/u/PJPJPJ)\ **Post date:** [April 15, 2009, 9:39am UTC](https://www.ruby-forum.com/t/complex-forms-only-one-level-of-a-oearrayn-essa-is-allowed/165558/1 "2009-04-15T09:39:01Z")
Hi all, I thought I was trying to do something rather simple, but it has caused me a lot of headaches. Here it is: - in my program: model\_a has\_many model\_b. model\_b has\_many model\_c. - in the user interface, I would like the user to be able to fill the information for one model\_a, one or more associated model\_bs (corresponding fields could be added with a set of links ‘add/remove a model\_b’), and for each model\_b added, one or more model\_c (with the same mechanism). Thanks to the great tutorial “Handle multiple models in one form”, it’s easy to handle the first step (any number of model\_b per model\_a), but I can’t get the second step to work. The natural indexing should (I think) be: “model\_a[model\_b\_attributes][][model\_c\_attributes][][an\_attribute]” But it doesn’t seem to work. I read here > **[Action View Form Helpers — Ruby on Rails Guides](https://guides.rubyonrails.org/form_helpers.html)** > > Action View Form HelpersForms in web applications are an essential interface for user input. However, form markup can quickly become tedious to write and maintain because of the need to handle form control naming and its numerous attributes. Rails... that “only one level of “arrayness” is allowed” and that I should use hashes instead, but I am not quite sure I understand how to do it. Do you have any idea? Thanks a lot PJ ---
**Author:** ![PJPJPJ](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/6bbea6/32.png) [@PJPJPJ](https://www.ruby-forum.com/u/PJPJPJ)\ **Post date:** [April 15, 2009, 10:05am UTC](https://www.ruby-forum.com/t/complex-forms-only-one-level-of-a-oearrayn-essa-is-allowed/165558/2 "2009-04-15T10:05:59Z")
On Apr 15, 1:07 am, PJ [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > “model\_a[model\_b\_attributes][][model\_c\_attributes][][an\_attribute]” > > But it doesn’t seem to work. I read herehttp://guides.rubyonrails.org/form\_helpers.html > that “only one level of “arrayness” is allowed” and that I should use > hashes instead, but I am not quite sure I understand how to do it. > > Do you have any idea? What that comment is saying is that you can replace an array eg [a,b,c] with a hash eg {1 =\> a, 2=\> b, 3=\>c} Generating those keys is up to your client side code, approaches included using a number you increment or going for some unique thing you generate on the spot (eg time in milliseconds concatenated with a random number) so that you don’t have to keep track of how many fields and what not you have created clientside. Fred ---
**Author:** ![PJPJPJ](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/6bbea6/32.png) [@PJPJPJ](https://www.ruby-forum.com/u/PJPJPJ)\ **Post date:** [April 15, 2009, 6:10pm UTC](https://www.ruby-forum.com/t/complex-forms-only-one-level-of-a-oearrayn-essa-is-allowed/165558/3 "2009-04-15T18:10:20Z")
Thanks Fred. Considering there is a bit of “wizardry” that needs to be done and that Rails doesn’t include helpers to do this simply, does it mean it is not recommended to build such complex forms? I am not very experienced with Rails, but I love the fact it is very “clean” and I feel a bit cautious having to generate keys manually. PJ On Apr 15, 9:05 am, Frederick C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) ---
**Author:** ![PJPJPJ](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/6bbea6/32.png) [@PJPJPJ](https://www.ruby-forum.com/u/PJPJPJ)\ **Post date:** [April 15, 2009, 10:30pm UTC](https://www.ruby-forum.com/t/complex-forms-only-one-level-of-a-oearrayn-essa-is-allowed/165558/4 "2009-04-15T22:30:36Z")
PJ wrote: […] > The natural > indexing should (I think) be: > > “model\_a[model\_b\_attributes][][model\_c\_attributes][][an\_attribute]” > > But it doesn’t seem to work. > […] There is a bug in Rails at least up to 2.2.2 that you may be running into. I reported it on this list around Christmas 2008. If you search the archives for my name around that time, you will find the ensuing discussion and a patch that Fred submitted for the bug. Good luck! ## Best, Marnen Laibow-Koser [http://www.marnen.org](http://www.marnen.org) removed\_email\_address@domain.invalid ---
**Author:** ![PJPJPJ](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/6bbea6/32.png) [@PJPJPJ](https://www.ruby-forum.com/u/PJPJPJ)\ **Post date:** [April 15, 2009, 6:40pm UTC](https://www.ruby-forum.com/t/complex-forms-only-one-level-of-a-oearrayn-essa-is-allowed/165558/5 "2009-04-15T18:40:19Z")
On Apr 15, 5:09 pm, PJ [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Thanks Fred. > > Considering there is a bit of “wizardry” that needs to be done and > that Rails doesn’t include helpers to do this simply, does it mean it > is not recommended to build such complex forms? > > I am not very experienced with Rails, but I love the fact it is very > “clean” and I feel a bit cautious having to generate keys manually. There is the nested forms stuff in rails 2.3 (unfortunately not yet documented in the guide). Fred