# Dynamic form fields

**URL:** <https://www.ruby-forum.com/t/dynamic-form-fields/110502>\
**Category:** Rails\
**Created:** [July 26, 2007, 10:21pm UTC](https://www.ruby-forum.com/t/dynamic-form-fields/110502 "2007-07-26T22:21:27Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![visaolive](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/v/57b2e6/32.png) [@visaolive](https://www.ruby-forum.com/u/visaolive)\
**Post date:** [July 26, 2007, 10:21pm UTC](https://www.ruby-forum.com/t/dynamic-form-fields/110502/1 "2007-07-26T22:21:27Z")

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Hi, i know is a very common problem this one but i have been searching  
for information about the best way (rails way) of doing this and i  
haven’t met a good solution:

I have a model named Contact that has many phone numbers. I want to  
have a form that dynamically add/delete 2 fields: phone number and a  
category (home, personal, work, etc). I’m doing this with RJS, no  
problem with that.

The question would be, is there a way of naming the fields and use  
form\_for :contact and send and hash/array of these lines and add them  
as new relationships.

I read about parsing something like contact[phones][][number] but  
haven’t found much more info.

Thanks you in advance!

---

<div class="post-metadata">

**Author:** ![visaolive](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/v/57b2e6/32.png) [@visaolive](https://www.ruby-forum.com/u/visaolive)\
**Post date:** [July 29, 2007, 3:16pm UTC](https://www.ruby-forum.com/t/dynamic-form-fields/110502/2 "2007-07-29T15:16:15Z")

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Emilio T. wrote:

> The question would be, is there a way of naming the fields and use  
> form\_for :contact and send and hash/array of these lines and add them  
> as new relationships.
> 
> I read about parsing something like contact[phones][][number] but  
> haven’t found much more info.

This is something I struggled with for a little while on the first Rails  
app I built back with Rails pre-1.0 - it seemed like the path of least  
resistance has always involved treating each relationship add/edit as a  
separate event, updating the model immediately. However, what I really  
wanted to do was to have a form where you could edit the master record  
and some associated details at the one time, adding and deleting detail  
records as needed on the form, but only saving all changes back to the  
database when the user submitted.

In the end I managed to come up with a solution that works quite well  
for me - well enough that I haven’t really checked to see if there is a  
better way of doing this with the current Rails release, so my solution  
may be able to be refined further… anyway, here is what I came up  
with:

View  
On the view side in the form, you’ll have the master fields for your  
Contact object in the usual fashion, and then name the detail object  
fields for the number and contact after the association on the master  
object. Thus if Contact has\_many :phone\_numbers, I would name my detail  
object fields as phone\_number[0][number], phone\_number[0][category],  
phone\_number[1][number], etc. In truth, the numbers don’t matter - they  
only exist to uniquely identify each detail record within the form  
submission.

Adding/Deleting Detail Records  
This can be done a couple of different ways - I’ve used both RJS  
rendering a partial with a session variable keeping track of the next  
number to use, and javascript in the browser to insert/delete detail  
records. I prefer the latter approach now, but it requires writing  
javascript rather than using RJS to shield you from it.

Controller  
Most of the difficulty was in the controller, since I needed a way to  
process all the edits in one create/update action, and I wanted a way to  
do this that could be re-used on different forms. I ended up writing a  
module to handle this logic in a generic fashion, and now just include  
it into my Application controller base class when the same need arises.

The module defines a single save method that takes a couple of  
parameters: the name of the param that defines the master object values  
(e.g. contact), and the name (or names) of the object(s) in the params  
hash that define the values for each instance of the detail class(es):  
phone\_number in this example. (Note though that you can for example  
create multiple detail objects for several different associations at  
once if you need to - such as a contact with many phone numbers and many  
email addresses).

By convention, I require the param keys to be named after the  
association on the master object, so that I can use  
reflect\_on\_associations to find all the other info I need to  
create/update the detail objects. It’s then a matter of  
locating/updating or creating both the master and all the detail  
records, and keeping a track of any detail records that may need to be  
deleted if they are not also in the submitted params. All of this is  
done inside a transaction, so that if a validation error occurs on say a  
detail attribute, the whole save can be rolled back.

Anyway, that’s an explanation of how the code works - if you’d like a  
copy, I’d be happy to email it to you.

Cheers,

Adam