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2010-Mar-18 13:43 UTC

hash in controller is nil after submitting form

I''m trying to create a data entry form but getting an error when it
sumbmits.  I am using an hash to get the names of the fields definied
in the controller''s "new" function:

  def new
    @thing = thing.new
    @columns = Hash.new

    @columns[''thing_general''] = [
            ["title","name"],
            ["number","num"],

   etc...

and then I access it in the object''s new.html.erb:

  <% for c in @columns[''thing_general''] do %>
     <tr>
       <td class="name">
       <label
for="<%=c.first%>"><%=c.first%></label></td>
       <td>
       <input id="<%=c.second%>"
name="thing[<%=c.second
%>]"type="text" /></td>
       </td>

the first time I load the page, the correct form displays but then
when I click submit, I get this error :

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

Extracted source (around line #38):

35:   <tr><td><hr/></td></tr>
36:
37:   <tbody>
38:    <% for c in @columns[''thing_general''] do %>
39:      <tr>
40:        <td class="name">
41:        <label
for="<%=c.first%>"><%=c.first%></label></td>



why would it get a nil object when I submit the form (after working
the first time) and why is it trying to load the same page after
submitting?

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Michael Pavling

2010-Mar-18 13:49 UTC

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Re: hash in controller is nil after submitting form

On 18 March 2010 13:43, ES
<emstolfo-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> the first time I load the page, the correct form displays but then
> when I click submit, I get this error :
>
> You have a nil object when you didn''t expect it!
> You might have expected an instance of ActiveRecord::Base.
> The error occurred while evaluating nil.[]
>
> why would it get a nil object when I submit the form (after working
> the first time) and why is it trying to load the same page after
> submitting?
When you click submit, you''re probably going through the
"create"
method (unless you''ve set the form to go somewhere else)... does the
@columns[''thing_general''] value get populated there
(you''ve shown the
code for the "new" method, but not "create")?

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Colin Law

2010-Mar-18 13:50 UTC

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Re: hash in controller is nil after submitting form

On 18 March 2010 13:43, ES
<emstolfo-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> I''m trying to create a data entry form but getting an error when
it
> sumbmits.  I am using an hash to get the names of the fields definied
> in the controller''s "new" function:
>
>  def new
>    @thing = thing.new
>    @columns = Hash.new
>
>    @columns[''thing_general''] = [
>            ["title","name"],
>            ["number","num"],
>
>   etc...
>
> and then I access it in the object''s new.html.erb:
>
>  <% for c in @columns[''thing_general''] do %>
>     <tr>
>       <td class="name">
>       <label
for="<%=c.first%>"><%=c.first%></label></td>
>       <td>
>       <input id="<%=c.second%>"
name="thing[<%=c.second
> %>]"type="text" /></td>
>       </td>
>
> the first time I load the page, the correct form displays but then
> when I click submit, I get this error :
>
> You have a nil object when you didn''t expect it!
> You might have expected an instance of ActiveRecord::Base.
> The error occurred while evaluating nil.[]
>
> Extracted source (around line #38):
>
> 35:   <tr><td><hr/></td></tr>
> 36:
> 37:   <tbody>
> 38:    <% for c in @columns[''thing_general''] do %>
> 39:      <tr>
> 40:        <td class="name">
> 41:        <label
for="<%=c.first%>"><%=c.first%></label></td>
>
>
>
> why would it get a nil object when I submit the form (after working
> the first time) and why is it trying to load the same page after
> submitting?
I presume that when you click it is calling a controller action, then
for whatever reason rendering the page again, but this time @columns
is not setup, hence the error.  Have a look at the action called by
the submit and see what you have told it to do.  Also have a look in
development.log and you may get a clue.  Guessing at what the code may
do, possibly the submit requests a save that fails so you are
re-rendering the page to allow the user to make a correction, but you
have not setup @columns.

Colin

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2010-Mar-18 13:53 UTC

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Re: hash in controller is nil after submitting form

yes I am going through create, should I make the @columns hash a class
variable or just repopulate it in the create method?

On Mar 18, 2:49 pm, Michael Pavling
<pavl...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> On 18 March 2010 13:43, ES
<emsto...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> > the first time I load the page, the correct form displays but then
> > when I click submit, I get this error :
>
> > You have a nil object when you didn''t expect it!
> > You might have expected an instance of ActiveRecord::Base.
> > The error occurred while evaluating nil.[]
>
> > why would it get a nil object when I submit the form (after working
> > the first time) and why is it trying to load the same page after
> > submitting?
>
> When you click submit, you''re probably going through the
"create"
> method (unless you''ve set the form to go somewhere else)... does
the
> @columns[''thing_general''] value get populated there
(you''ve shown the
> code for the "new" method, but not "create")?
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Michael Pavling

2010-Mar-18 14:05 UTC

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Re: Re: hash in controller is nil after submitting form

On 18 March 2010 13:53, ES
<emstolfo-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> yes I am going through create, should I make the @columns hash a class
> variable or just repopulate it in the create method?
You can do it however you like; you just need to make sure it''s not nil
;-)

Personally... I would make a decision based on the object and the purpose:
 - I *doubt* it''s really likely to be best as a class variable
 - repopulate it if that''s easiest, but consider refactoring the
population out to a private method to reuse it
 - Could it be that this variable may really make more sense as a constant?
 - Maybe other factors come into play that aren''t evident from your
posting...

To be honest... I''m not sure I like the idea of the controller telling
the view which fields to display - maybe this functionality would be
better off in a view helper - but that''s a different conversation, and
it''s your code :-/

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Colin Law

2010-Mar-18 14:08 UTC

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Re: Re: hash in controller is nil after submitting form

On 18 March 2010 13:53, ES
<emstolfo-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> yes I am going through create, should I make the @columns hash a class
> variable or just repopulate it in the create method?
You could populate it in a before or after_filter on those actions.  I
have to say that the whole thing looks a bit odd.  Are you sure it
should not be in a view helper for example?

Colin

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2010-Mar-18 14:16 UTC

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Re: hash in controller is nil after submitting form

hmmm, I''m totally new to this, what exactly is a helper used for?  For
these kinds of constant-type things in a view?

On Mar 18, 3:08 pm, Colin Law
<clan...-gM/Ye1E23mwN+BqQ9rBEUg@public.gmane.org>
wrote:> On 18 March 2010 13:53, ES
<emsto...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> > yes I am going through create, should I make the @columns hash a class
> > variable or just repopulate it in the create method?
>
> You could populate it in a before or after_filter on those actions.  I
> have to say that the whole thing looks a bit odd.  Are you sure it
> should not be in a view helper for example?
>
> Colin
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Colin Law

2010-Mar-18 14:24 UTC

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Re: Re: hash in controller is nil after submitting form

On 18 March 2010 14:16, ES
<emstolfo-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> hmmm, I''m totally new to this, what exactly is a helper used for?
 For
> these kinds of constant-type things in a view?
This is a reasonable introduction -
http://paulsturgess.co.uk/articles/show/49-using-helper-methods-in-ruby-on-rails

Colin

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2010-Mar-18 14:27 UTC

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Re: hash in controller is nil after submitting form

ok, thanks!

On Mar 18, 3:24 pm, Colin Law
<clan...-gM/Ye1E23mwN+BqQ9rBEUg@public.gmane.org>
wrote:> On 18 March 2010 14:16, ES
<emsto...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> > hmmm, I''m totally new to this, what exactly is a helper used
for?  For
> > these kinds of constant-type things in a view?
>
> This is a reasonable introduction
-http://paulsturgess.co.uk/articles/show/49-using-helper-methods-in-ru...
>
> Colin
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