Rails - Feb 2006 - accessing associated models in a validate method

Why can''t I access an associated model in a validate method?  I have  
some code that looks like the following:

Models:
class Product < ActiveRecord::Base
   has_many: upcs
end

class Upc < ActiveRecord::Base
   belongs_to :product
   def validate
     errors.add_on_blank(''upc'') unless product.new_record?
   end
end

Controller:
def create
   @product = Product.new(params[:product])
   @upc = Upc.new(params[:upc])
   @product.upcs << @upc unless @upc.upc.empty?

   if @product.save
     # ...
   end
end

When the create method gets called I get the NoMethodError "The error  
occured while evaluating nil.new_record?"  Why is product nil?  How  
can I access associated models in a validate method.

Thanks.

Eddie Hillenbrand wrote:
> Why can''t I access an associated model in a validate method?  I
have
> some code that looks like the following:
> 
> Models:
> class Product < ActiveRecord::Base
>   has_many: upcs
> end
> 
> class Upc < ActiveRecord::Base
>   belongs_to :product
>   def validate
>     errors.add_on_blank(''upc'') unless product.new_record?
>   end
> end
> 
> Controller:
> def create
>   @product = Product.new(params[:product])
>   @upc = Upc.new(params[:upc])
>   @product.upcs << @upc unless @upc.upc.empty?
> 
>   if @product.save
>     # ...
>   end
> end
> 
> When the create method gets called I get the NoMethodError "The error
> occured while evaluating nil.new_record?"  Why is product nil?  How 
can
> I access associated models in a validate method.
The "unless @upc.upc.empty?" code will stop @upc.product being set to
@product if upc is the empty string, so validate can''t see it.  Why
don''t you remove this condition and add a "validates_associated
:upcs"
line to Product, so that @product and its new upcs''s will only save if
everything''s valid.

-- 
We develop, watch us RoR, in numbers too big to ignore.

On Feb 10, 2006, at 3:37 AM, Mark Reginald James wrote:
> The "unless @upc.upc.empty?" code will stop @upc.product being
set to
> @product if upc is the empty string, so validate can''t see it. 
Why
> don''t you remove this condition and add a
"validates_associated :upcs"
> line to Product, so that @product and its new upcs''s will only
save if
> everything''s valid.
Even with "unless @upc.upc.empty?" commented out "product"
is still
nil in the validate method.

The requirements for the app are such that a product can be created  
without a UPC, but once a product is saved a blank UPC can''t be  
added.  If you know a way to do this with the validation class  
methods, please elaborate, I''d really like a better way to do this.

Eddie Hillenbrand wrote:
> Even with "unless @upc.upc.empty?" commented out
"product" is still  nil
> in the validate method.
> 
> The requirements for the app are such that a product can be created  
> without a UPC, but once a product is saved a blank UPC can''t be 
added.
> If you know a way to do this with the validation class  methods, please 
> elaborate, I''d really like a better way to do this.
Is it that a product''s UPC can start off blank, but once it''s
set can''t return to being blank; or is it that the UPC must be
set no later than the first save after creation?

Also, try changing "product.new_record?" to
"self.product.new_record?".
That sometimes fixes these problems for reasons I can''t yet fathom.

-- 
We develop, watch us RoR, in numbers too big to ignore.