One solution is to create a new model for the association. It schould be the case
if you add attributes to the association (because push_with_attributes is now deprecated).
You can then simply find the association given the ids of your linked object and call destroy.

However, when you don’t have any attribute in your liaison, the has_and_belongs_to_many
is nicer to work with. (you don’t need a rails model for the liaison.)
Here is a link to the methods
has_and_belongs_to_many adds where we can read :

"collection.delete(object, …) - removes one or more objects from the
collection by removing their associations from the join table.
This does not destroy the objects."

Let’s assume we dispose of 2 models ‘Post’ and ‘Category’ with a N-N association :

class Post < ActiveRecord::Base
  has_and_belongs_to_many :categories
end

class Category < ActiveRecord::Base
  has_and_belongs_to_many :posts
end

To delete an association (remove a post from a category) you can use this method :

  def remove_post_from_category
     post = Post.find(params[:post][:id])
     category = post.categories.find(params[:category][:id])

     if category
        post.categories.delete(category)
     end

  end

This function will destroy the association but won’t destroy the category.

You can also removes all the categories from the posts by using :

collection.clear - removes every object from the collection.
This does not destroy the objects.

In our example :

post.categories.clear

One way to avoid those errors is to redirect the browser to the root /favicon.ico file.
Just add this line in the /public/.htaccess file of your rails project :

 RewriteRule ^(.*)favicon.ico$ favicon.ico [QSA]

Do you use another method to resolve this problem ?

1. The first way uses has_and_belongs_to_many in both models. You’ll have to create a join table that has no corresponding model or primary key. ( ActiveRecord will look by default for a join table called groups_users )

class Group < ActiveRecord::Base
has_and_belongs_to_many :users # foreign keys in the join table
end
class User < ActiveRecord::Base
has_and_belongs_to_many :groups # foreign keys in the join table
end


The join table can have more attributes which can be filled with the push_with_attributes method:

class User < ActiveRecord::Base
has_and_belongs_to_many :groups # foreign keys in the join table

def join_group(group)
groups.push_with_attributes(group, :joined_at => Time.now)
end
end

2. The second way uses a has_many association with the :through option and a join model:
   class Subscriptions < ActiveRecord::Base
belongs_to :group # foreign key - programmer_id
belongs_to :user # foreign key - project_id
end
class Group :subscriptions
end
class User :subscriptions
end


If you have to work with the relationship model as its own entity, thent you'll need to use has_many :through. Otherwise, you can just stick to has_and_belongs_to_many.

(click to enlarge) :

This plugin depends on GraphViz, which you can find here.

From your rails application root, run :

ruby script/plugin install

svn://rubyforge.org//var/svn/visualizemodels/visualize_models

rake visualize_models

You’ll then find your .png images in the “doc” directory.

Scriptaculous offers a nice autocompletion component that integrates quite well with Ruby on Rails.Here is a link that shows different ways to plug it in your rails application:

http://www.slash7.com/articles/2005/08/13/ajaxariffic-au…

Everybody knows how to validate the uniqueness of a field in a database :

validates_uniqueness_of :date

If you now want to validate the uniqueness of a couple (ex: date,user_id) here’s how you can:

validates_uniqueness_of :date, :scope => :user_id

wget http://rubyforge.org/frs/download.php/3463/rubygems-0.8.8.tgz
tar vxzf rubygems-0.8.8.tgz
cd rubygems-0.8.8
ruby setup.rb

gem update
gem install rails