many_to_many associations in rails

This has been a nightmare for me and I'm willing to give an arm and an eyeball to the person who can help me :P I'm going to explain this as best as possible.

When a user edits their 'profile' they can type in skills that they have in nested attributes fields (they can click 'Add Another Skill' an开发者_开发知识库d it will populate another field for them to type). When they begin to type, jquery-autocomplete kicks in. They MUST select an item from autocomplete. When they save, for example, 3 skills, we get this:

table: skills

+-----------+----------------+
|  user_id  |     skill      |
+-----------+----------------+
|     4     |  Photoshop     |
+-----------+----------------+
|     4     |  Illustrator   |
+-----------+----------------+
|     4     |  InDesign      |
+-----------+----------------+

Now, what I want to do is NOT store the actual skill names. Instead, I want to store the ID of the skill from skills_vocabulary list (which is what the jquery-autocomplete uses).

table: skills_vocabulary

+------+----------------+
|  id  |     skill      |
+------+----------------+
|  1   |  Illustrator   |
+------+----------------+
|  2   |  Dreamweaver   |
+------+----------------+
|  3   |  After Effects |
+------+----------------+
|  4   |  InDesign      |
+------+----------------+
|  5   |  Photoshop     |
+------+----------------+
|  6   |  Flash         |
+------+----------------+

THUS, the skills table should look like this:

+-----------+----------------+
|  user_id  |    skill_id    |
+-----------+----------------+
|     4     |        5       |
+-----------+----------------+
|     4     |        1       |
+-----------+----------------+
|     4     |        4       |
+-----------+----------------+

Any help would be greatly, greatly, greatly appreciated. I've been at war with this for an embarrassing 3 months.

Thank you all.

EDIT/

<%= f.fields_for :skills do |builder| %>
    <%= render "skills_fields", :f => builder %>
  <% end %>
  <p><%= link_to_add_fields "Add a Skill", f, :skills %></p>     

_skills_fields.html.erb

<div class="fields ac skills">
    <div class="clearfix">
        <span class="left"><%=f.autocomplete_field :name, users_autocomplete_skills_vocab_name_path, :class => 'restricted_to_autocomplete' %></span><span class="remove_link left"><%= link_to_remove_fields "[x]", f %></span>
    </div>
</div>

EDIT 2/

Right now it's just

skill.rb

class Skill < ActiveRecord::Base
  belongs_to :user
end

user.rb

class User < ActiveRecord::Base
  has_many :tskills, :dependent => :destroy
  accepts_nested_attributes_for :tskills, :allow_destroy => true, :reject_if => lambda { |a| a[:name].blank? }
end

skills_vocabulary.rb

class SkillsVocabulary < ActiveRecord::Base

end

My controller code is the basic index, show, new, create, update, destroy

The list of skills (about 10,000 items long) is in the table skills_vocabularies

This should be your classes:

class User < ActiveRecord::Base
  has_and_belongs_to_many :skills
end

class Skill < ActiveRecord::Base
  has_and_belongs_to_many :users
end

and this is the migration which creates them

class CreateUsers < ActiveRecord::Migration
  def self.up
    create_table :users do |t|
      t.string :name
      t.timestamps
    end
  end

  def self.down
    drop_table :users
  end
end

class CreateSkills < ActiveRecord::Migration
  def self.up
    create_table :skills do |t|
      t.string :name
      t.timestamps
    end
  end

  def self.down
    drop_table :skills
  end
end

class SkillsUsers < ActiveRecord::Migration
  def self.up
    create_table :skills_users, :id => false do |t|
      t.integer :skill_id
      t.integer :user_id
    end
  end

  def self.down
    drop_table :skills_users
  end
end

then add a new skill is as simple as

user.skills << Skill.find(1) # to add a skill
user.skills = Skill.all      # to add many of them

Look here fo further details

Update: I ve tried the autocomplete gem and I think you should accept the Rubish Gupta suggestion, i.e. use my models plus jquery token input because it will handle pretty well many-to-many associations. Autocomplete gem as far as I saw is for 1-to-n associations.

Moreover you have a full working example in rails to play with.