Tagging Models

Sometimes you need to tag your models with tokens, think tagging images with keywords or including hashtags in a twitter post.

And in a slightly more rare situation, you sometimes may want to have multiple types of tags for your products. Like in an ecommerce store, you may want to have a style, color, type, or generic tags attached to your product model. These tags could be used in an recommendation engine to help determine what products are similar to other products.

Create the Style Model

This is your basic many to many relationship between your style model and your products model.

```ruby db/migrations/create_styles_table.rb

create_table :styles do |t|
  t.string :name, null: false
  t.timestamps
end

create_table :products_styles, id: false do |t|
  t.integer :product_id, null: false
  t.integer :style_id, null: false
end ```

Creating the tags concern

Because effectively all of the tags are going to have the same attributes (namely :name), I want to have all of that common code in a Concern that will be included in all of the different types of tags

My concern looks like this

```ruby app/models/concerns/taggable.rb module Taggable extend ActiveSupport::Concern

included do validate :name, presence: true

has_and_belongs_to_many :products
before_save :downcase_name   end

def downcase_name name.downcase! end end

I want to only save the lower case name and I want to automatically report the relationship between products and the taggable attribute.  This will reduce the noise in the database.

# Create the Model
Now because I am using a concern, my models should be really thin and only look like this

```ruby app/models/concerns/taggable.rb
class Style < ActiveRecord::Base
  include Taggable
end

Adding and removing tags

Using the jQuery tokenizer extension, you can follow the guide at Rails casts to hook into your model. While his approach is dandy and all, we have multiple types of tags attached to our product and there is a faster way to manage the addition methods on our model.

His method requires that you have a method like below for every one of your token attributes. This is going to make your products model huge as you add more and more taggable attributes.

```ruby app/models/concerns/taggable.rb has_and_belongs_to_many :authors

def author_tokens=(ids) self.author_ids = ids.split(“,”) end

We can reduce this code creep by using Ruby meta programming.  I want to have an array of all of the taggable attributes that product can have and it should automatically create the necessarily methods and relationships between products and this taggable item.

```ruby app/models/product.rb
  ATTRIBUTES = %w(style)

  ATTRIBUTES.each do |status_name|
    has_and_belongs_to_many status_name.pluralize.to_sym

    define_method "#{status_name}_ids=" do |ids|
      self.send (status_name.pluralize + "="), ids.split(',').map {|c| status_name.pluralize.singularize.camelize.constantize.find(c.to_i) }
    end 

  end

Now as add more and more taggable items to the product model, it will automatically create the [attribute_name]_ids methods that the jQuery needs to attach these tokens onto our model. The more taggable attributes I add, the more code I save.

Alternative approach

You could argue that I could of put all of the tags in one table and used STI to break each type into different models. While this could work if all of the tags had the same name type of string, you may want your name attribute to be an integer. Having them in separate tables will also reduce the table size, thus making the results run a little bit quicker.

Conclusion

Like always, feel free to hit me up in the chat. My chat tool is hooked into Google Talk, free too drop me a message if you have any questions. Cheers.