Strange error. Don't know what to ask

Hi guys,

I’m puzzled by an error I’m getting in my app.

I have some declarations in my show method:

GET /tabs/1

GET /tabs/1.xml

def show
@tab = Tab.find(params[:id])
@videos = Video.find(:all, :conditions => [“tab_id = ?”, params[:id]])
@video = @tab.videos.build
@comment = @tab.comments.build

respond_to do |format|
format.html # show.html.erb
format.xml { render :xml => @tab }
end
end

I have objects called tab. Users can add comments and videos to tabs.
From the show view I want to be able to create a video and comment. It
goes fine for the videos. That’s why the @tab.videos/comments.build are
there.

Now. As said everything is ok with the videos.

In the view I have one part with this:

<% for comment in @tab.comments.reverse %> <%=h comment.created_by %> <%=h comment.created_at.to_s(:short) %> <%=h comment.body %>
<% end %>

So I can simply list the comments for a tab.

But but, when I have the line @comment = @tab.comments.build in the
controller. I get the next error:

wrong number of arguments (1 for 0)

In the line:
<%=h comment.created_by %> <%=h comment.created_at.to_s(:short)
%> <%=h comment.body %>

The strange thing is that if I remove the .to_s(:short) in that line
there is no problem.

I can’t find a reason why the .to_s(:short) and @comment =
@tab.comments.build cause that.

Do you have any hints?

Thanks.

On Apr 9, 2008, at 4:21 PM, comopasta Gr wrote:

@tab = Tab.find(params[:id])

@tab.comments.build cause that.

Do you have any hints?

Thanks.

That comment has yet to be saved and thus has no created_at. Well, to
be precise, comment.created_at is nil. Now, NilClass#to_s exists, but
takes no arguments. The Time#to_s has be redefined by ActiveSupport
to take a format symbol. Your error is from a call to nil.to_s(:short)

In your view you could either test for nil? or do something like:
<%= comment.new_record? ? ‘(unsaved)’ :
comment.created_at.to_s(:short) %>
a test of comment.created_at.nil? would be an equally valid condition,
but this seems more intention-revealing.

-Rob

Rob B. http://agileconsultingllc.com
[email protected]

comopasta Gr wrote:

@comment = @tab.comments.build

At this point, @tab.comments now contains a new, uninitialised comment
with nil valued attributes (including the timestamps).

comment.created_at.to_s(:short)

One of the comments is the above mentioned uninitialised one so for this
one comment.created_at is nil which responds to #to_s but not with an
argument.

If the @comment instance variable is there for a form, then use:

@comment = Comment.new

instead.

Ok. Now your comments helped me spotting an error in my code. The point
is that in the same “show” view I can list the existing comments for
that tab and also create a new comment for the tab. Separate issues.

So I use one object to read the existing ones:
@comments = Comment.find(:all, :conditions => [“tab_id = ?”,
params[:id]])

And another to be able to create new one:
@comment = @tab.comments.build


My error was that in the view I was not using the @comments to iterate
the existing comments.

I was using: @tab.comments.reverse directly used from the view.

So, instead of using that I am now using @comments.reverse and the
errors are gone.

Thanks!

It’s probably because whatever object is being sent “to_s” isn’t the
object you think it is.

It’s probably nil, which would mean to_s would work, but to_s(:short)
won’t.

After you’ve built, created_at will be nil, which will set up the case
that I just described.

Set an initial value for it in the controller, and all will be good.

@comment = @tab.comments.build(:created_at => Time.now)

or

@comment = @tab.comments.build; @comment.created_at = Time.now

Julian.

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