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Matthew Lang

2007-Jun-19 14:19 UTC

Nil object for nested resource

Hi all,

I have 2 models with a standard 1 to many relationship.  I''m also using
REST on the two models and have added the appropriate code to the
routes.rb file.

scorecard.rb:
class Scorecard < ActiveRecord::Base
  has_many :attributes
end

attribute.rb:
class Attribute < ActiveRecord::Base
  belongs_to :scorecard
end

routes.rb:
map.resources :scorecards do |scorecard|
  scorecard.resources :attributes
end

My problem is that I want to show a single scorecard with all it''s
attributes.  I then want to display a "New attribute" link to add a
new
attribute to the current scorecard.

scorecards/show.rhtml:
<%= label_for("scorecard") %>
<%=h @scorecard.name %><br />

<%= label_for("template") %>
<%=h @scorecard.template %>

<b>Attributes:</b>
<table>
<% for attribute in @scorecard.attributes %>
  <tr>
    <td><%=h attribute.name %></td>
    <td><%=h attribute.weight %></td>
  </tr>
<% end %>
</table>
<%= link_to "New Attribute", new_attribute_path(@scorecard) %>

However I get the message for line 17 (last line) when I try to view
this page,

You have a nil object when you didn''t expect it!
The error occurred while evaluating nil.to_sym

I have tried checking against various REST and Rails books and articles,
and I thought I had used the correct syntax for creating a link to a new
attribute from this scorecard.

Any help on this would be greatly appreciated.

Thanks,

Matthew

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Matthew Lang

2007-Jun-20 14:38 UTC

head link

Nil object for nested resource

Hi all,

I have 2 models with a standard 1 to many relationship.  I''m also
using
REST on the two models and have added the appropriate code to the
routes.rb file.

# scorecard.rb:
class Scorecard < ActiveRecord::Base
  has_many :attributes
end

# attribute.rb:
class Attribute < ActiveRecord::Base
  belongs_to :scorecard
end

# routes.rb:
map.resources :scorecards do |scorecard|
  scorecard.resources :attributes
end

My problem is that I want to show a single scorecard with all it''s
attributes.  I then want to display a "New attribute" link to add a
new
attribute to the current scorecard.

# scorecards/show.rhtml:
<%= label_for("scorecard") %>
<%=h @scorecard.name %><br />

<%= label_for("template") %>
<%=h @scorecard.template %>

<b>Attributes:</b>
<table>
<% for attribute in @scorecard.attributes %>
  <tr>
    <td><%=h attribute.name %></td>
    <td><%=h attribute.weight %></td>
  </tr>
<% end %>
</table>
<%= link_to "New Attribute", new_attribute_path(@scorecard) %>

However I get the message for line 17 (last line) when I try to view
this page,

You have a nil object when you didn''t expect it!
The error occurred while evaluating nil.to_sym

I have tried checking against various REST and Rails books and
articles,
and I thought I had used the correct syntax for creating a link to a
new
attribute from this scorecard.

Any help on this would be greatly appreciated.

Thanks,

Matthew


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jparker

2007-Jun-20 19:25 UTC

head link

Re: Nil object for nested resource

I think you may need to rename your Attribute model. ActiveRecord
objects already have an instance variable named "attributes" which
holds the attributes for the given model instance. The Scorecard''s
has_many :attributes collection and the pre-existing attributes hash
are probably colliding.

-John

On Jun 19, 7:19 am, Matthew Lang
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:> Hi all,
>
> I have 2 models with a standard 1 to many relationship.  I''m also
using
> REST on the two models and have added the appropriate code to the
> routes.rb file.
>
> scorecard.rb:
> class Scorecard < ActiveRecord::Base
>   has_many :attributes
> end
>
> attribute.rb:
> class Attribute < ActiveRecord::Base
>   belongs_to :scorecard
> end
>
> routes.rb:
> map.resources :scorecards do |scorecard|
>   scorecard.resources :attributes
> end
>
> My problem is that I want to show a single scorecard with all it''s
> attributes.  I then want to display a "New attribute" link to add
a new
> attribute to the current scorecard.
>
> scorecards/show.rhtml:
> <%= label_for("scorecard") %>
> <%=h @scorecard.name %><br />
>
> <%= label_for("template") %>
> <%=h @scorecard.template %>
>
> <b>Attributes:</b>
> <table>
> <% for attribute in @scorecard.attributes %>
>   <tr>
>     <td><%=h attribute.name %></td>
>     <td><%=h attribute.weight %></td>
>   </tr>
> <% end %>
> </table>
> <%= link_to "New Attribute", new_attribute_path(@scorecard)
%>
>
> However I get the message for line 17 (last line) when I try to view
> this page,
>
> You have a nil object when you didn''t expect it!
> The error occurred while evaluating nil.to_sym
>
> I have tried checking against various REST and Rails books and articles,
> and I thought I had used the correct syntax for creating a link to a new
> attribute from this scorecard.
>
> Any help on this would be greatly appreciated.
>
> Thanks,
>
> Matthew
>
> --
> Posted viahttp://www.ruby-forum.com/.

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Matthew Lang

2007-Jun-21 10:11 UTC

head link

Re: Nil object for nested resource - Solved

Problem solved!

In the routes.rb file I had the following

map.resources :scorecards do |scorecard|
  scorecard.resources :perspectives
end

map.resources :perspectives do |perspective|
  perspective.resources: scores
end

when I should have had

map.resources :scorecards do |scorecard|
  scorecard.resources :perspectives do |perspective|
    perspective.resources :score
  end
end


Thanks,

Matthew


On Jun 20, 8:25 pm, jparker
<johncpar...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> I think you may need to rename your Attribute model. ActiveRecord
> objects already have an instance variable named "attributes"
which
> holds the attributes for the given model instance. The Scorecard''s
> has_many :attributes collection and the pre-existing attributes hash
> are probably colliding.
>
> -John
>
> On Jun 19, 7:19 am, Matthew Lang
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
> wrote:
>
> > Hi all,
>
> > I have 2 models with a standard 1 to many relationship.  I''m
also using
> > REST on the two models and have added the appropriate code to the
> > routes.rb file.
>
> > scorecard.rb:
> > class Scorecard < ActiveRecord::Base
> >   has_many :attributes
> > end
>
> > attribute.rb:
> > class Attribute < ActiveRecord::Base
> >   belongs_to :scorecard
> > end
>
> > routes.rb:
> > map.resources :scorecards do |scorecard|
> >   scorecard.resources :attributes
> > end
>
> > My problem is that I want to show a single scorecard with all
it''s
> > attributes.  I then want to display a "New attribute" link
to add a new
> > attribute to the current scorecard.
>
> > scorecards/show.rhtml:
> > <%= label_for("scorecard") %>
> > <%=h @scorecard.name %><br />
>
> > <%= label_for("template") %>
> > <%=h @scorecard.template %>
>
> > <b>Attributes:</b>
> > <table>
> > <% for attribute in @scorecard.attributes %>
> >   <tr>
> >     <td><%=h attribute.name %></td>
> >     <td><%=h attribute.weight %></td>
> >   </tr>
> > <% end %>
> > </table>
> > <%= link_to "New Attribute",
new_attribute_path(@scorecard) %>
>
> > However I get the message for line 17 (last line) when I try to view
> > this page,
>
> > You have a nil object when you didn''t expect it!
> > The error occurred while evaluating nil.to_sym
>
> > I have tried checking against various REST and Rails books and
articles,
> > and I thought I had used the correct syntax for creating a link to a
new
> > attribute from this scorecard.
>
> > Any help on this would be greatly appreciated.
>
> > Thanks,
>
> > Matthew
>
> > --
> > Posted viahttp://www.ruby-forum.com/.

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