Rails - Mar 2006 - :dependent => :destroy

Hi,

There is something I don''t understand about :dependent => :destroy.
I
hope someone can help me. Consider this code:

class Folder < ActiveRecord::Base
   has_many :myfiles
   has_many :folders
   has_many :group_folders, :dependent => :destroy

   validates_uniqueness_of :name, :scope => "folder_id"
   validates_presence_of :name

   before_destroy :dont_destroy_folder_with_contents
   # Folders containing files or sub-folders
   # can not be deleted
   def dont_destroy_folder_with_contents
     if self.folders.length > 0 or self.myfiles.length > 0
       raise "Can''t destroy folder with contents"
     end
   end
end

It prevents folders with contents from being deleted, however the 
group_folders do get deleted because of :dependent => :destroy. How can 
I prevent the group_folders from being destroyed when a folder "has 
contents"? I do want the group_folders to be destroyed when the folder 
is destroyed without a problem.

Thanks.

Mischa.

Anyone...?

Mischa Berger wrote:
> Hi,
> 
> There is something I don''t understand about :dependent =>
:destroy. I
> hope someone can help me. Consider this code:
> 
> class Folder < ActiveRecord::Base
>   has_many :myfiles
>   has_many :folders
>   has_many :group_folders, :dependent => :destroy
> 
>   before_destroy :dont_destroy_folder_with_contents
>   # Folders containing files or sub-folders
>   # can not be deleted
>   def dont_destroy_folder_with_contents
>     if self.folders.length > 0 or self.myfiles.length > 0
>       raise "Can''t destroy folder with contents"
>     end
>   end
> end
> 
> It prevents folders with contents from being deleted, however the 
> group_folders do get deleted because of :dependent => :destroy. How can 
> I prevent the group_folders from being destroyed when a folder "has 
> contents"? I do want the group_folders to be destroyed when the folder
> is destroyed without a problem.
> 
> Thanks.
> 
> Mischa.

2006/3/12, Mischa Berger <spmm_pls@yahoo.com>:
>    before_destroy :dont_destroy_folder_with_contents
>    # Folders containing files or sub-folders
>    # can not be deleted
>    def dont_destroy_folder_with_contents
>      if self.folders.length > 0 or self.myfiles.length > 0
>        raise "Can''t destroy folder with contents"
>      end
>    end
> end
Did you try returning false from here ?  I think that is what you are
supposed to do to prevent an action.

Hope that helps !
--
Fran?ois Beausoleil
http://blog.teksol.info/

> Did you try returning false from here ?  I think that is what you are
> supposed to do to prevent an action.
Yeah, tried that and the group_folders still get deleted...

OK, someone on IRC helped me out.

This is the way to do it:

class Folder < ActiveRecord::Base
   has_many :myfiles
   has_many :folders
   has_many :group_folders

   before_destroy :dont_destroy_folder_with_contents
   # Folders containing files or sub-folders
   # can not be deleted
   def dont_destroy_folder_with_contents
     if self.folders.length > 0 or self.myfiles.length > 0
       raise "Can''t destroy folder with contents"
     end
   end

   after_destroy :destroy_dependant_group_folders
   # Delete dependant group_folders
   # This code should be executed after_destroy
   def destroy_dependant_group_folders
     for group_folder in self.group_folders
       group_folder.destroy
     end
   end
end

On 3/13/06, Mischa Berger <spmm_pls@yahoo.com> wrote:
>    after_destroy :destroy_dependant_group_folders
>    # Delete dependant group_folders
>    # This code should be executed after_destroy
>    def destroy_dependant_group_folders
>      for group_folder in self.group_folders
>        group_folder.destroy
>      end
>    end
> end
But what if one or some of the group_folder.destroy commands fail?

You could use a transaction to make sure that this entire destroy is
an all or none change to the db.

-Peter

> But what if one or some of the group_folder.destroy commands fail?
> 
> You could use a transaction to make sure that this entire destroy is
> an all or none change to the db.
Thanks for the suggestion, but I don''t think this is neccesary in my 
situation.