# Error handling!

**URL:** <https://www.ruby-forum.com/t/error-handling/50610>\
**Category:** Rails\
**Created:** [December 19, 2005, 3:20am UTC](https://www.ruby-forum.com/t/error-handling/50610 "2005-12-19T03:20:57Z")\
**Posts on this page:** 8\
**Page:** 1

<div class="post-metadata">

**Author:** ![welly](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/f0a364/32.png) [@welly](https://www.ruby-forum.com/u/welly)\
**Post date:** [December 19, 2005, 3:20am UTC](https://www.ruby-forum.com/t/error-handling/50610/1 "2005-12-19T03:20:57Z")

</div>

Hello all,

I’m in the beginning states of learning ruby on rails development and  
have got to a part where I’m a little stuck! Basically writing a simple  
blog application, just to try something completely different! 😉

I have a page which displays the current blog entry, it’s comments and  
at the bottom of the page, a form to add a comment. So far, so good.  
It’ll add comments, list them etc. So I decided I need a validation  
routine going on and used “validates\_presence\_of :name” in my comments  
model. This is the problem I’m facing now. In past examples I’ve looked  
at, for example when you’ve just scaffolded a page, the page seems to  
submit back to itself if there’s an error and displays the error using

\<% error\_messages\_for ‘post’ %\>

However, the way this seems to be working which is the same method that  
the “creating a weblog in 15 minutes” video uses, the page will never  
return to itself and so cannot display the error. It simply says  
“comment added” and posts not passing the validation routine will not be  
added. So I changed the code and have got this going on -

def comment  
@comment = Post.find(params[:id]).comments.create(params[:comment])  
if @comment.save  
flash[:notice] = “added your comment.”  
redirect\_to :action =\> “show”, :id =\> params[:title]  
else  
flash[:notice] = “not added your comment.”  
render :action =\> “show”, :id =\> params[:title]  
end  
end

Now this works, but am unable to make use of error\_messages for ‘post’  
and unable to display the reason why the comment was not added (no name  
was entered).

Help! 🙂 Any suggestions how I go about this?

Thanks!

Alastair

---

<div class="post-metadata">

**Author:** ![welly](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/f0a364/32.png) [@welly](https://www.ruby-forum.com/u/welly)\
**Post date:** [December 19, 2005, 4:42am UTC](https://www.ruby-forum.com/t/error-handling/50610/2 "2005-12-19T04:42:05Z")

</div>

You need something like the following in your view (comment.rhtml  
possibly or show.rhtml):

```
<% error_messages_for 'comment' %>

```

and if the save fails you could render the action you’re in if you  
want to stay on the same page:

```
render :action => 'comment'
```

---

<div class="post-metadata">

**Author:** ![welly](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/f0a364/32.png) [@welly](https://www.ruby-forum.com/u/welly)\
**Post date:** [December 19, 2005, 5:36am UTC](https://www.ruby-forum.com/t/error-handling/50610/3 "2005-12-19T05:36:09Z")

</div>

I assume show is being called prior to someone posting a comment on a  
post? If so, that invocation of show does not have an @comment  
instance variable set.

Your best bet is to change the show.rhtml to have an \<%  
error\_messages\_for ‘post’ %\> (if it’s even needed there) and change  
the code in the comment method to render :action =\> ‘comment’ if the  
save fails. Be sure to include \<% error\_messages\_for ‘comment’ %\> in  
comment.rhtml. This should give you the errors you’re looking for  
and leave the user on the comment screen so they can correct it.

---

<div class="post-metadata">

**Author:** ![welly](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/f0a364/32.png) [@welly](https://www.ruby-forum.com/u/welly)\
**Post date:** [December 19, 2005, 4:45am UTC](https://www.ruby-forum.com/t/error-handling/50610/4 "2005-12-19T04:45:06Z")

</div>

Steven S. wrote:

> You need something like the following in your view (comment.rhtml  
> possibly or show.rhtml):
> 
> ```
> <% error_messages_for 'comment' %>
> 
> ```
> 
> and if the save fails you could render the action you’re in if you want  
> to stay on the same page:
> 
> ```
> render :action => 'comment'
> 
> ```

Hi Steve,

Thanks for the reply. I tried putting \<% error\_messages\_for ‘comment’ %\>  
at the top of my show.rhtml file and got and error of

You have a nil object when you didn’t expect it!  
You might have expected an instance of ActiveRecord::Base.  
The error occured while evaluating nil.errors

Extracted source (around line #1):

1: \<% error\_messages\_for ‘comment’ %\>  
2: \<%= render :partial =\> “post”, :object =\> @post %\>  
3:  
4:

### Comments

The show.rhtml file currently looks like -

\<% error\_messages\_for ‘comment’ %\>

\<%= render :partial =\> “post”, :object =\> @post %\>

### Comments
\<% for comment in @post.comments %\> \<%= comment.body %\>
* * *
\<% end %\>

\<%= form\_tag :action =\> “comment”, :id =\> @post, :title =\> @post.title  
%\>

Name  
  
\<%= text\_field “comment”, “name”, :size =\> 50 %\>

```
<p>
	<label for="comment_email">Email</label><br>
	<%= text_field "comment", "email", :size => 50 %>
</p>

<p>
	<label for="comment_url">Website</label><br>
	<%= text_field "comment", "url", :size => 50 %>
</p>

<label for="comment_body">Comment</label><br>
<%= text_area "comment", "body", :columns => 30, :rows => 5 %><br>
<%= submit_tag "Comment!" %>

```

Any ideas?

Thanks!

Alastair

---

<div class="post-metadata">

**Author:** ![welly](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/f0a364/32.png) [@welly](https://www.ruby-forum.com/u/welly)\
**Post date:** [December 19, 2005, 10:27pm UTC](https://www.ruby-forum.com/t/error-handling/50610/5 "2005-12-19T22:27:28Z")

</div>

Steven S. wrote:

> 

Yeah, show is being called, which displays the blog entry plus the  
comments form, so I can see how it wouldn’t have an @comment instance  
now.

The problem with the error message being in the comment.rhtml file is  
that the comment.rhtml is ideally never called as the comments form is  
shown in the show.rhtml file and that is where I’d like to show the  
errors. I did create a comments.rhtml file, and put \<%=  
error\_messages\_for ‘comments’ as the only line in the file and that  
worked and displayed the correct error. However, I would prefer for it  
to be shown in the show.rhtml file if possible

thanks!

Alastair

---

<div class="post-metadata">

**Author:** ![welly](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/f0a364/32.png) [@welly](https://www.ruby-forum.com/u/welly)\
**Post date:** [December 20, 2005, 12:13am UTC](https://www.ruby-forum.com/t/error-handling/50610/6 "2005-12-20T00:13:54Z")

</div>

How about you put the following code in show.rhtml:

```
<% if @comment -%>
     	<%= error_messages_for 'comment' %>
<% end -%>

```

This way if you have no @comment instance variable it won’t cause the  
nil object error.

Also, you’d need to change the render :action back to ‘show’.

---

<div class="post-metadata">

**Author:** ![welly](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/f0a364/32.png) [@welly](https://www.ruby-forum.com/u/welly)\
**Post date:** [December 20, 2005, 12:01am UTC](https://www.ruby-forum.com/t/error-handling/50610/7 "2005-12-20T00:01:50Z")

</div>

> 

I’ve put my application online -

[http://kozmo.railsplayground.com/blog/show/First+blog+posting](http://kozmo.railsplayground.com/blog/show/First+blog+posting)

If you enter a comment but leave the name out, that is what is  
happening. It works, but it’s not ideal. Any thoughts on how I can  
display the error on the “show” page?

Cheers!

Alastair

---

<div class="post-metadata">

**Author:** ![welly](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/f0a364/32.png) [@welly](https://www.ruby-forum.com/u/welly)\
**Post date:** [December 20, 2005, 12:59am UTC](https://www.ruby-forum.com/t/error-handling/50610/8 "2005-12-20T00:59:03Z")

</div>

Steven S. wrote:

> 

Many thanks! that did the trick. I also had to get the current record in  
the comment method, so it looks like

def comment  
@comment = Post.find(params[:id]).comments.create(params[:comment])

if @comment.save  
flash[:notice] = “added your comment.”  
redirect\_to :action =\> “show”, :id =\> params[:title]  
else  
render :action =\> ‘show’, id =\> params[:title]  
end  
end

but all works now! 🙂

Cheers for the help!

Alastair