Rails - Mar 2006 - Verifying existance of related record

Is there an easy way to validate that a related record exists?

I''ve got a table that contains a set of categories and I want to make  
sure the user has entered a vaild category (i.e. a category that exists  
in the categories table).  So in the model of the table I put this:



class Master < ActiveRecord::Base
  belongs_to :category, :foreign_key => "categoryid"

  validates_presence_of :categoryid

  def validate_on_create
    unless Category.find(:first, :conditions => "categoryid =
#{categoryid}")
      errors.add(:categoryid, "is not a valid category id")
    end
  end
end


However this does not work because the "validate_on_create" is being
run
before the "validates_presence_of", so if the categoryid is nil the  
category.find throws an SQL syntax exception.

I would have thought that the belongs_to would check for the existance  
of the related row.  No?



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All you need is:

class Master < ActiveRecord::Base
   belongs_to :category, :foreign_key => "categoryid"

   validates_presence_of :category, :message => "is not a valid  
category"
end

or something like that.

On Mar 16, 2006, at 1:47 PM, Richard Williams wrote:
>
> Is there an easy way to validate that a related record exists?
>
> I''ve got a table that contains a set of categories and I want to
make
> sure the user has entered a vaild category (i.e. a category that  
> exists
> in the categories table).  So in the model of the table I put this:
>
>
>
> class Master < ActiveRecord::Base
>   belongs_to :category, :foreign_key => "categoryid"
>
>   validates_presence_of :categoryid
>
>   def validate_on_create
>     unless Category.find(:first, :conditions => "categoryid = # 
> {categoryid}")
>       errors.add(:categoryid, "is not a valid category id")
>     end
>   end
> end
>
>
> However this does not work because the "validate_on_create" is  
> being run
> before the "validates_presence_of", so if the categoryid is nil
the
> category.find throws an SQL syntax exception.
>
> I would have thought that the belongs_to would check for the existance
> of the related row.  No?
>
>
>
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> Posted with http://DevLists.com.  Sign up and save your time!
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> Rails mailing list
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Thanks.  I figured I was overcomplicating this.  That worked perfectly.



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