# Best practices - field initialization based on display rules **URL:** \ **Category:** Rails\ **Created:** [July 17, 2006, 7:48pm UTC](https://www.ruby-forum.com/t/best-practices-field-initialization-based-on-display-rules/98724 "2006-07-17T19:48:46Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![weyus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7ab992/32.png) [@weyus](https://www.ruby-forum.com/u/weyus)\ **Post date:** [July 17, 2006, 7:48pm UTC](https://www.ruby-forum.com/t/best-practices-field-initialization-based-on-display-rules/98724/1 "2006-07-17T19:48:46Z")
All, I have a form with the following field interaction rules. Given checkbox A, text field B text field C If checkbox A is checked then make text field C equal to the value of text field B and disable field C. If checkbox A is unchecked then enable field C. In order to display a form where I’m manipulating an already existing object, I have something like this in my RHTML template to display text field C: \<%= (@obj.field\_B == @obj.field\_C) ? text\_field(:obj, ‘field\_C’, :disabled =\> ‘true’) : text\_field(:obj, ‘field\_C’, :disabled =\> ‘false’) %\> Should I put this logic in a helper so as to simplify my template and keep this small bit of business logic out of it? I already have Javascript that would force this behavior for me given the checked status of the checkbox - should I just call that Javascript function in an onLoad() handler? Should I use an onLoad handler that executes an AJAX call to handle setting up these fields correctly - then I could just add AJAX calls to default other fields as well? (seems a little excessive to me). Thanks, Wes ---
**Author:** ![weyus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7ab992/32.png) [@weyus](https://www.ruby-forum.com/u/weyus)\ **Post date:** [July 17, 2006, 8:39pm UTC](https://www.ruby-forum.com/t/best-practices-field-initialization-based-on-display-rules/98724/2 "2006-07-17T20:39:44Z")
On Monday, July 17, 2006, at 7:48 PM, Wes G. wrote: > Should I put this logic in a helper so as to simplify my template and > Thanks, > Wes > > – > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). > > * * * > > Rails mailing list > removed\_email\_address@domain.invalid > [http://lists.rubyonrails.org/mailman/listinfo/rails](http://lists.rubyonrails.org/mailman/listinfo/rails) I would do this in two steps… First… use your controller to set the proper state of instance variables so that the rules are enforced when an object is loaded in. This way you don’t need any JS to play around with the initial settings. You can also set the enabled/disabled state of controls like this. Second… I would use the KRJS plugin to enforce the rules once the page has been loaded. It’s pretty simple to add an AJAX response to an ‘onchange’ event and then embed the RJS in the controller. This keeps the business logic out of the view. In theory you could write a JS library that does all the validation on the client side, but I wouldn’t trust that route. It’s not very DRY. \_Kevin [www.sciwerks.com](http://www.sciwerks.com) ---
**Author:** ![weyus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7ab992/32.png) [@weyus](https://www.ruby-forum.com/u/weyus)\ **Post date:** [July 17, 2006, 9:16pm UTC](https://www.ruby-forum.com/t/best-practices-field-initialization-based-on-display-rules/98724/3 "2006-07-17T21:16:29Z")
Kevin O. wrote: > On Monday, July 17, 2006, at 7:48 PM, Wes G. wrote: > > > Should I put this logic in a helper so as to simplify my template and > > Thanks, > > Wes > > > > – > > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). > > > > * * * > > > > Rails mailing list > > removed\_email\_address@domain.invalid > > [http://lists.rubyonrails.org/mailman/listinfo/rails](http://lists.rubyonrails.org/mailman/listinfo/rails) > > I would do this in two steps… > > First… use your controller to set the proper state of instance > variables so that the rules are enforced when an object is loaded in. > This way you don’t need any JS to play around with the initial settings. > You can also set the enabled/disabled state of controls like this. > > Second… I would use the KRJS plugin to enforce the rules once the page > has been loaded. It’s pretty simple to add an AJAX response to an > ‘onchange’ event and then embed the RJS in the controller. This keeps > the business logic out of the view. > > In theory you could write a JS library that does all the validation on > the client side, but I wouldn’t trust that route. It’s not very DRY. > > \_Kevin > [www.sciwerks.com](http://www.sciwerks.com) Kevin, I take your point on the DRYness of a client-side approach. On the other hand, what I’m needing to do in the view doesn’t really need any information from the server so doing a POST just to do AJAX somehow seems excessive (probably because it’s ingrained in me that doing the POST is expensive, even though I know it’s not because it’s not the whole page worth of data going back and forth). But I see your point and I’d consider an AJAX approach. However, I’m not sure I get you on this point: “You can also set the enabled/disabled state of controls like this.” Do you mean set up a variable in my model to represent the state of the edit field in my view (e.g. enabled vs. disabled)? If so, I would think that that sort of thing would belong in a “form model” object (what in the Java world we call a form bean, which is simply responsible for tracking the state of form elements). Thanks, Wes ---
**Author:** ![weyus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7ab992/32.png) [@weyus](https://www.ruby-forum.com/u/weyus)\ **Post date:** [July 17, 2006, 10:49pm UTC](https://www.ruby-forum.com/t/best-practices-field-initialization-based-on-display-rules/98724/4 "2006-07-17T22:49:13Z")
On Monday, July 17, 2006, at 9:16 PM, Wes G. wrote: > > > Rails mailing list > > > Second… I would use the KRJS plugin to enforce the rules once the page > > Thanks, > Wes > > – > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). > > * * * > > Rails mailing list > removed\_email\_address@domain.invalid > [http://lists.rubyonrails.org/mailman/listinfo/rails](http://lists.rubyonrails.org/mailman/listinfo/rails) Something like that. I sometimes put code in my views like this… \<%= text\_field ‘model’,‘attribute’, :disabled=\>@model.some\_method %\> this works when the page is first loaded to set the initial state but you then need to worry about it from then on. Regarding the AJAX thing… I just do what is easiest to implement and then optimize it later if it becomes a problem. Using something like the KRJS plugin, it’s almost trivial to implement this sort of thing. \_Kevin [www.sciwerks.com](http://www.sciwerks.com)