Rails - May 2005 - has_and_belongs_to_many dual insert error ?

Hi !

(See references at the end)

I have a slight problem.  Whenever I save one of my domain models, which 
contains an has_and_belongs_to_many relationship with another one, the 
relationships are doubled.

My domain is a series of pictures, where each picture can be tagged with 
one or more words.  So, a picture of my dog could be tagged "Jordy, Dog, 
Dog 2005", for example.

In my form, the tags are presented to the user in a single INPUT 
type="text".  The user edits the list, and separates the words using a
comma.

Then, my controller splits everything back, and asks the Picture domain 
object to update it''s tags.

The implementation is at the bottom, but the end result is that I get 
two rows like this:

INSERT INTO pictures_tags(picture_id, tag_id) VALUES (13, 21);
INSERT INTO pictures_tags(picture_id, tag_id) VALUES (13, 21);

If I add a unique index to pictures_tags, MySQL rejects the second 
insert, as it should.

The only way I found to prevent that problem is to save my picture 
first, and then to update the tags.

Is that behavior expected ?  What am I doing wrong ?  Should 
has_and_belongs_to_many be defined on both domain objects ?

Thanks for any tips !
François

R E F E R E N C E S
==================
SQL Tables
----------
create table pictures (
     id int primary key auto_increment,
     title varchar(80)
);

create table tags (
     id int primary key auto_increment,
     tag varchar(32)
);

Domain objects
--------------
class Picture < ActiveRecord::Base
     has_and_belongs_to_many :tags

     def update_tags(tags)
         tags = tags.collect! {|name| name.downcase}
         reject_invalid_tags(tags)
         remove_deleted_tags(tags)
         reject_existing_tags(tags)
         add_tags_to_picture(tags)
     end

protected
     def reject_invalid_tags(tags)
         tags.reject! { |name| name.nil? or name.empty? }
     end

     def remove_deleted_tags(tags)
         self.tags.each {|tag|
             self.tags.delete(tag) unless tags.include?(tag.tag)
         }
     end

     def reject_existing_tags(tags)
         self.tags.each { |tag| tags.delete tag.tag.downcase }
     end

     def add_tags_to_picture(tags)
         tags.each do |name|
             tag = Tag.find_by_tag(name.downcase) ||
                 Tag.create(''tag'' => name.downcase)
             self.tags.push(tag)
         end
     end
end

class Tag < ActiveRecord::Base
     has_and_belongs_to_many :pictures

     def to_s() self.tag.capitalize end
     def ==(other) return self.tag == other.tag end
     def <=>(other) return self.tag <=> other.tag end
end

Controller
----------
class PhotoController < ApplicationController
     def save
         pict = @params[''picture'']

         picture = Picture.new
         picture.original = main_image
         picture.title = pict[''title'']
         picture.body = pict[''body'']
         picture.author = author

         # Adding these lines prevents the problem from
         #   occuring:
         # picture.save
         # picture.reload

         picture.update_tags(pict[''tags''].split(/\s*,\s*/))
         picture.save
     end
end

I am having a similar problem.

Except I haven''t tested it out because the project was put on hold for
another project... I have a habtm association (on each end of the
habtm) and without even having the controller actions to change
anything but the number of times one of the habtm-ed models has been
viewed (ie: this haiku has been read 15 times) all of the habtm
associations get doubled.

I''m not even sure when it happens (because i haven''t tested
it) but
some time after checking to see if the association importation worked
all the associations are doubled (ie: a haiku with a tag of summer now
has two tags, summer and summer).

If I get some time I''ll try and uncover when it is occuring.

-Caleb

On 5/23/05, François Beausoleil <fbeausoleil-IQIa899fVSs@public.gmane.org>
wrote:
> Hi !
> 
> (See references at the end)
> 
> I have a slight problem.  Whenever I save one of my domain models, which
> contains an has_and_belongs_to_many relationship with another one, the
> relationships are doubled.
> 
> My domain is a series of pictures, where each picture can be tagged with
> one or more words.  So, a picture of my dog could be tagged "Jordy,
Dog,
> Dog 2005", for example.
> 
> In my form, the tags are presented to the user in a single INPUT
> type="text".  The user edits the list, and separates the words
using a
> comma.
> 
> Then, my controller splits everything back, and asks the Picture domain
> object to update it''s tags.
> 
> The implementation is at the bottom, but the end result is that I get
> two rows like this:
> 
> INSERT INTO pictures_tags(picture_id, tag_id) VALUES (13, 21);
> INSERT INTO pictures_tags(picture_id, tag_id) VALUES (13, 21);
> 
> If I add a unique index to pictures_tags, MySQL rejects the second
> insert, as it should.
> 
> The only way I found to prevent that problem is to save my picture
> first, and then to update the tags.
> 
> Is that behavior expected ?  What am I doing wrong ?  Should
> has_and_belongs_to_many be defined on both domain objects ?
> 
> Thanks for any tips !
> François
> 
> R E F E R E N C E S
> ==================> 
> SQL Tables
> ----------
> create table pictures (
>      id int primary key auto_increment,
>      title varchar(80)
> );
> 
> create table tags (
>      id int primary key auto_increment,
>      tag varchar(32)
> );
> 
> Domain objects
> --------------
> class Picture < ActiveRecord::Base
>      has_and_belongs_to_many :tags
> 
>      def update_tags(tags)
>          tags = tags.collect! {|name| name.downcase}
>          reject_invalid_tags(tags)
>          remove_deleted_tags(tags)
>          reject_existing_tags(tags)
>          add_tags_to_picture(tags)
>      end
> 
> protected
>      def reject_invalid_tags(tags)
>          tags.reject! { |name| name.nil? or name.empty? }
>      end
> 
>      def remove_deleted_tags(tags)
>          self.tags.each {|tag|
>              self.tags.delete(tag) unless tags.include?(tag.tag)
>          }
>      end
> 
>      def reject_existing_tags(tags)
>          self.tags.each { |tag| tags.delete tag.tag.downcase }
>      end
> 
>      def add_tags_to_picture(tags)
>          tags.each do |name|
>              tag = Tag.find_by_tag(name.downcase) ||
>                  Tag.create(''tag'' => name.downcase)
>              self.tags.push(tag)
>          end
>      end
> end
> 
> class Tag < ActiveRecord::Base
>      has_and_belongs_to_many :pictures
> 
>      def to_s() self.tag.capitalize end
>      def ==(other) return self.tag == other.tag end
>      def <=>(other) return self.tag <=> other.tag end
> end
> 
> Controller
> ----------
> class PhotoController < ApplicationController
>      def save
>          pict = @params[''picture'']
> 
>          picture = Picture.new
>          picture.original = main_image
>          picture.title = pict[''title'']
>          picture.body = pict[''body'']
>          picture.author = author
> 
>          # Adding these lines prevents the problem from
>          #   occuring:
>          # picture.save
>          # picture.reload
> 
>         
picture.update_tags(pict[''tags''].split(/\s*,\s*/))
>          picture.save
>      end
> end
> 
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