Testing for non-existent parameters with "if"

Rails
1

Rails gives me an error when I test for a blank param like this:

    if params[:post][:id]
      @comment.commentable = Post.find(params[:post][:id])
    elsif params[:event][:id]
      @comment.commentable = Event.find(params[:event][:id])
    end

If I have params[:post][:id], things are fine. But if I have
params[:event][:id] instead, I get this error:

You have a nil object when you didn’t expect it!
You might have expected an instance of Array.
The error occurred while evaluating nil.[]

Rails dies when it checks for the non-existent params[:post][:id]. I
will always send either :event or :post, but never both. How can I use
“if - elsif” to test for this without crashing? Thanks!

2

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Hi Taylor,

On 3-Mar-07, at 11:09 PM, Taylor S. wrote:

You have a nil object when you didn’t expect it!
You might have expected an instance of Array.
The error occurred while evaluating nil.[]

Rails dies when it checks for the non-existent params[:post][:id]. I
will always send either :event or :post, but never both. How can I
use
“if - elsif” to test for this without crashing? Thanks!

If the params[:post] hash is non-existent, then checking within it
to see if there’s an :id value is probably what’s throwing that error.

To avoid this problem you’d want to do something like:

if params[:post] && params[:post][:id]
@comment.commentable = Post.find(params[:post][:id])
elsif params[:event] && params[:event][:id]
@comment.commentable = Event.find(params[:event][:id])
end

Or you could do something like this:

if id = params[:post][:id] rescue nil
@comment.commentable = Post.find(id)
elsif id = params[:event][:id] rescue nil
@comment.commentable = Event.find(id)
end

Thanks,

Dan

Dan K.
Autopilot Marketing Inc.

Email: [email protected]
Phone: 1 (604) 820-0212
Web: http://autopilotmarketing.com/
vCard: http://autopilotmarketing.com/~dan.kubb/vcard

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3

Taylor S. wrote:

You have a nil object when you didn’t expect it!
You might have expected an instance of Array.
The error occurred while evaluating nil.[]

Rails dies when it checks for the non-existent params[:post][:id]. I
will always send either :event or :post, but never both. How can I use
“if - elsif” to test for this without crashing? Thanks!

It depends on what is nil, i.e. params[:post] or params[:post][:id] but
you can do something like:

if params[:post].has_key?(:id)

or

if not params[:post][:id] == nil

–
Michael W.

4

Rails gives me an error when I test for a blank param like this:

    if params[:post][:id]

If I have params[:post][:id], things are fine. But if I have
params[:event][:id] instead, I get this error:
And a third solution yet
if defined? params[:post][:id]
else
end

It will not always work if you use it from a view (because of how local
variables are handled), but for Models, Controllers and the sort it
should be fine.

regards,
javier ramirez

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5

Thanks to all - these solutions worked. I ended up using “if
params[:post] && params[:post][:id]”