# How Redisplay Failed User Data in Form?

**URL:** <https://www.ruby-forum.com/t/how-redisplay-failed-user-data-in-form/120523>\
**Category:** Rails\
**Created:** [November 17, 2007, 11:01pm UTC](https://www.ruby-forum.com/t/how-redisplay-failed-user-data-in-form/120523 "2007-11-17T23:01:57Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![S-gw](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/ed655f/32.png) [@S-gw](https://www.ruby-forum.com/u/S-gw)\
**Post date:** [November 17, 2007, 11:01pm UTC](https://www.ruby-forum.com/t/how-redisplay-failed-user-data-in-form/120523/1 "2007-11-17T23:01:57Z")

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Forms. Specifically entering data, submitting, discovering validation  
error, redisplaying the form with user’s entered data and error  
messages.

I know how I would approach it left to my own devices (described  
below), but wondering if there’s an idiomatic Rails way.

The classic “How To” stuff shows setting values of form elements  
directly from models. Well, that’s spiffy if nothing goes wrong, but  
in the above sequence of events, that approach doesn’t work.

Normally, in the controller I would load the model with data, I would  
then create a form data object (“FDO”) with a placeholder for each  
field that applies to the user-entered data in the form. I would  
populate the HTML input values with the contents of this FDO. So,  
value="\<%= fdo.firstName %\>" not value="\<%= model.firstName %\>"

To populate the FDO I test params to see if the form had already been  
submitted. If yes, I populate the FDO by copying values from params.  
If not, I populate the FDO by copying original data from the model.

This way the form sees virgin data from the database/model when the  
form is first displayed, and then the tainted data from user input if  
the form is redisplayed.

Does Rails have anything built in for this process, or is the  
developer left to implement his own system like I describe above  
(which of course is fine with me).

– gw (www.railsdev.ws)

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**Author:** ![S-gw](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/ed655f/32.png) [@S-gw](https://www.ruby-forum.com/u/S-gw)\
**Post date:** [November 18, 2007, 1:00am UTC](https://www.ruby-forum.com/t/how-redisplay-failed-user-data-in-form/120523/2 "2007-11-18T01:00:44Z")

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Hello Greg,

It sounds like a lot of work 🙂 Here is a typical method in a  
controller:

def update  
@post = Post.new(params[:post])  
if @post.save  
redirect\_to post\_path(@post)  
else  
render :action =\> ‘edit’  
end

If the save is not successful it redisplays the edit view (form).

Would this work for your requirements? What are your concerns  
displaying properties from the model?

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<div class="post-metadata">

**Author:** ![S-gw](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/ed655f/32.png) [@S-gw](https://www.ruby-forum.com/u/S-gw)\
**Post date:** [November 18, 2007, 1:40am UTC](https://www.ruby-forum.com/t/how-redisplay-failed-user-data-in-form/120523/3 "2007-11-18T01:40:30Z")

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> What are your concerns displaying properties from the model?

I have the redisplay of the edit form working fine, but if there’s a  
validation error, the form is showing the original data coming from  
the database, and not the data that was just entered into the form.

So, in a field for numbers let’s say the form originally displays a  
value of 3 (which came from the db). The user edits it and writes  
“two” – right now when the validation fails, and we cycle back to  
the edit form, it is redisplaying 3 and not “two”. We don’t want the  
user to have to edit the form all over again, so we want data from  
the params values has to populate the HTML value attributes.

Something has to be in charge of using the database data the first  
time, but use the params data the second time around. The form is an  
interim container until we approve everything, and then the model  
gets updated.

– gw

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<div class="post-metadata">

**Author:** ![S-gw](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/ed655f/32.png) [@S-gw](https://www.ruby-forum.com/u/S-gw)\
**Post date:** [November 19, 2007, 5:46am UTC](https://www.ruby-forum.com/t/how-redisplay-failed-user-data-in-form/120523/4 "2007-11-19T05:46:12Z")

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Hmm. I’ve always validated before updating the model. Philosophically  
it seems undesireable to stuff the model with data that has not been  
vetted.

In a simplistic model that’s just a quick exchange of data with a one  
page turn-around, I suppose it doesn’t really matter so long as the  
save is prevented.

I guess if that’s the accepted way, I’ll give that a shot.

– gw

On Nov 18, 2007, at 8:01 AM, Nicholas H. wrote:

> ```
> render :action => 'edit'
> 
> ```
> 
> if this is not working for you perhaps you could post some code from
> 
> > validation error, the form is showing the original data coming from  
> > time, but use the params data the second time around. The form is an
> > 
> > > def update  
> > > displaying properties from the model?
> > > 
> > > > The classic “How To” stuff shows setting values of form elements
> > 
> > > > Does Rails have anything built in for this process, or is the  
> > > > developer left to implement his own system like I describe above  
> > > > (which of course is fine with me).

– gw (www.railsdev.ws)

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<div class="post-metadata">

**Author:** ![S-gw](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/ed655f/32.png) [@S-gw](https://www.ruby-forum.com/u/S-gw)\
**Post date:** [November 18, 2007, 5:02pm UTC](https://www.ruby-forum.com/t/how-redisplay-failed-user-data-in-form/120523/5 "2007-11-18T17:02:49Z")

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Sorry Greg, I screwed that example up:

It should have been something like this:

def update  
@post = Post.find(params[:id)  
@post.attributes = params[:post]  
if @post.save  
redirect\_to post\_path(@post)  
else  
render :action =\> ‘edit’  
end

Anyway, following something this will mean that the action (or view)  
will be rendered (if the model cannot be saved), displaying the data  
that the user entered, because the view will be feeding off the  
instance variable for the model with the attributes passed from user  
input (not the original values of the model), e.g.:

value = “\<%= @post.title %\>”

if this is not working for you perhaps you could post some code from  
your controller.

Cheers,  
Nicholas

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<div class="post-metadata">

**Author:** ![S-gw](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/ed655f/32.png) [@S-gw](https://www.ruby-forum.com/u/S-gw)\
**Post date:** [November 19, 2007, 1:50pm UTC](https://www.ruby-forum.com/t/how-redisplay-failed-user-data-in-form/120523/6 "2007-11-19T13:50:05Z")

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Greg,

Yes, it’s the Rails way to assign to the attributes and save/validate  
the model. If the model is not valid then it will not save. The save  
method calls #valid? to see if it has been saved or not - you can call  
this method as well - e.g. @post.valid?.

Cheers,  
Nicholas

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<div class="post-metadata">

**Author:** ![S-gw](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/ed655f/32.png) [@S-gw](https://www.ruby-forum.com/u/S-gw)\
**Post date:** [November 19, 2007, 2:03pm UTC](https://www.ruby-forum.com/t/how-redisplay-failed-user-data-in-form/120523/7 "2007-11-19T14:03:02Z")

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I implemented everything based on that approach and have it all working.

Thanks much!

– gw