Rails - Oct 2005 - Showing a neat error message

Hi All,

I''m trying to prevent users from deleting a folder that has contents 
like this:

class Folder < ActiveRecord::Base
	has_many :myfiles
	has_many :folders
	belongs_to :folder
	validates_uniqueness_of :name, :scope => "folder_id"
	
	before_destroy :dont_destroy_folder_with_contents
	def dont_destroy_folder_with_contents
	  if Folder.find(id) != nil || Myfile.find(id) != nil
	    raise "Cannot delete this folder because it has contents"
     end
   end
end

This works fine: the folder''s not deleted. However I do not get the
neat
error message with the red borders. I don''t seem to be able to figure 
out how to catch the exception and produce a neat error message. How do 
I get this working????

Thanks in advance!

Grt,
Mischa.

Hi,
In your controller, you need to catch the exception, so:
def destroy
  begin
    Folder.find(id).destroy
  rescue => e
    flash[:notice] = e
  end
end

Something like that..

2005/10/24, Mischa Berger:
> Hi All,
>
> I''m trying to prevent users from deleting a folder that has
contents
> like this:
>
> class Folder < ActiveRecord::Base
>         has_many :myfiles
>         has_many :folders
>         belongs_to :folder
>         validates_uniqueness_of :name, :scope => "folder_id"
>
>         before_destroy :dont_destroy_folder_with_contents
>         def dont_destroy_folder_with_contents
>           if Folder.find(id) != nil || Myfile.find(id) != nil
>             raise "Cannot delete this folder because it has
contents"
>      end
>    end
> end
>
> This works fine: the folder''s not deleted. However I do not get
the neat
> error message with the red borders. I don''t seem to be able to
figure
> out how to catch the exception and produce a neat error message. How do
> I get this working????
>
> Thanks in advance!
>
> Grt,
> Mischa.
>
> _______________________________________________
> Rails mailing list
> Rails-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
>

>         before_destroy :dont_destroy_folder_with_contents
>         def dont_destroy_folder_with_contents
>           if Folder.find(id) != nil || Myfile.find(id) != nil
>             raise "Cannot delete this folder because it has
contents"
>      end
What you want to be doing is running this code in the validate
function, something like:

def validate
  errors.add(:name_of_field_with_error, "cannot be deleted because it
has contents") if (Folder.find(id) != nil || Myfile.find(id) != nil)
end

At least that''s if I understood you correctly!

HTH

Luke

>> Folder.find(id)
This will throw an exception if id is not found, which might not be what
you want/expect. 

You could however use:

Folder.find_by_id(id)

which will return nil if id is not found

-----Original Message-----
From: rails-bounces-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
[mailto:rails-bounces-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org] On
Behalf Of Luke Randall
Sent: Monday, 24 October 2005 2:47 PM
To: rails-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
Subject: Re: [Rails] Showing a neat error message
>         before_destroy :dont_destroy_folder_with_contents
>         def dont_destroy_folder_with_contents
>           if Folder.find(id) != nil || Myfile.find(id) != nil
>             raise "Cannot delete this folder because it has
contents"
>      end
What you want to be doing is running this code in the validate
function, something like:

def validate
  errors.add(:name_of_field_with_error, "cannot be deleted because it
has contents") if (Folder.find(id) != nil || Myfile.find(id) != nil)
end

At least that''s if I understood you correctly!

HTH

Luke
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> This will throw an exception if id is not found, which might not be what
> you want/expect.
Quite right. Thanks for picking this up! =)

> What you want to be doing is running this code in the validate
> function, something like:
> 
> def validate
>   errors.add(:name_of_field_with_error, "cannot be deleted because it
> has contents") if (Folder.find(id) != nil || Myfile.find(id) != nil)
> end
> 
> At least that''s if I understood you correctly!
 From what I understood the validate function is only executed when 
you''re inserting or updating records, not when you are deleting.

>  From what I understood the validate function is only executed when
> you''re inserting or updating records, not when you are deleting.
Hmm, once again my bad =) Sorry, should have paid closer attention to
what you were trying to do. So what you are doing is right, having the
code in before_delete. However, if you are looking for the validation
style errors (with the red borders etc), you''d do something like this:

def before_destroy
  if (Folder.find(id) != nil || Myfile.find(id) != nil)
    errors.add(:name_of_field_with_error, "cannot be deleted because
it has contents")
    return false
  end
end

Be sure to change it to find_all (as above from Neville) if you don''t
want to raise an exception if no folder is found (and most likely you
don''t).

I haven''t tried this, but I think it should work. Assuming you
redirect_to an action which checks for errors for relevant model.
Hopefully this time I''ve got it right =)

Thanks for your help! Yeah, Neville was right, that''s not what I
wanted.
This is what I meant to do:

before_destroy :dont_destroy_folder_with_contents
	def dont_destroy_folder_with_contents
	  if Folder.find(:all, :conditions => ["folder_id = ?", id]) !=
nil ||
Myfile.find(:all, :conditions => ["folder_id = ?", id]) != nil
	    # raise "Cannot delete this folder because it has contents."
	    errors.add_to_base("Cannot delete this folder because it has 
contents.")
	    return false
     end
   end
> I haven''t tried this, but I think it should work. Assuming you
> redirect_to an action which checks for errors for relevant model.
> Hopefully this time I''ve got it right =)
I can''t figure out yet how to check for errors in the action
I''m
redirecting to. Do you have an example how to do this? I don''t seem to 
be able to access errors in the view or in the controller.

Thanks again,
Mischa.

An alternative which might be lighter/faster as it doesn''t instantiate
an ActiveRecord instance:

def before_destroy
  if (Folder.count("id = #{id}") > 0 || Myfile.count("id =
#{id}") > 0)
    errors.add(:name_of_field_with_error, "cannot be deleted because it
has contents")
    return false
  end
end 

-----Original Message-----
From: rails-bounces-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
[mailto:rails-bounces-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org] On
Behalf Of Luke Randall
Sent: Tuesday, 25 October 2005 5:54 AM
To: rails-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
Subject: Re: [Rails] Re: Showing a neat error message
>  From what I understood the validate function is only executed when 
> you''re inserting or updating records, not when you are deleting.
Hmm, once again my bad =) Sorry, should have paid closer attention to
what you were trying to do. So what you are doing is right, having the
code in before_delete. However, if you are looking for the validation
style errors (with the red borders etc), you''d do something like this:

def before_destroy
  if (Folder.find(id) != nil || Myfile.find(id) != nil)
    errors.add(:name_of_field_with_error, "cannot be deleted because it
has contents")
    return false
  end
end

Be sure to change it to find_all (as above from Neville) if you don''t
want to raise an exception if no folder is found (and most likely you
don''t).

I haven''t tried this, but I think it should work. Assuming you
redirect_to an action which checks for errors for relevant model.
Hopefully this time I''ve got it right =)
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Rails-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
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> I can''t figure out yet how to check for errors in the action 
> I''m redirecting to. Do you have an example how to do this? I
> don''t seem to be able to access errors in the view or in the
controller.

When you redirect, your rails app effectively gets a fresh new request
from the browser for the new url.

So your controller/request objects from the previous request are no
longer available unless you put/retrieve them from somewhere like  the
flash, which is saved/restored across requests or in a cookie or your
database

Take a look at:
http://api.rubyonrails.com/classes/ActionController/Flash.html 

-----Original Message-----
From: rails-bounces-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
[mailto:rails-bounces-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org] On
Behalf Of Neville
Burnell
Sent: Tuesday, 25 October 2005 10:26 AM
To: rails-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
Subject: RE: [Rails] Re: Showing a neat error message
> I can''t figure out yet how to check for errors in the action
I''m
> redirecting to. Do you have an example how to do this? I don''t
seem to
> be able to access errors in the view or in the
controller.

When you redirect, your rails app effectively gets a fresh new request
from the browser for the new url.

So your controller/request objects from the previous request are no
longer available unless you put/retrieve them from somewhere like  the
flash, which is saved/restored across requests or in a cookie or your
database _______________________________________________
Rails mailing list
Rails-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
http://lists.rubyonrails.org/mailman/listinfo/rails

> Take a look at:
> http://api.rubyonrails.com/classes/ActionController/Flash.html 
Thanks again for your help! One more question. In the examples in the 
API they''re only storing strings in the Flash. Is it possible to store 
the entire errors object in the flash too?

Thanks,
Mischa.

> In the examples in the API they''re only storing strings in the
Flash.
Is it possible to store the entire errors object in the flash too?

Yes, although there are some considerations:

1) the flash has to serializable, which should be the case for the
objects you are storing
2) the class has to be available to ruby/rails when the session is
reloaded on subsequent requests
3) large objects will have a resource cost to unload/load etc

If you have the AWDWR book, take a look at section 16.6, pg 322-324.

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