PolymorphicIntegerType

Rails' polymorphic associations are pretty useful. The example they give to set it up looks like:

class Picture < ActiveRecord::Base
  belongs_to :imageable, polymorphic: true
end
 
class Employee < ActiveRecord::Base
  has_many :pictures, as: :imageable
end
 
class Product < ActiveRecord::Base
  has_many :pictures, as: :imageable
end

With a migration that looks like:

class CreatePictures < ActiveRecord::Migration
  def change
    create_table :pictures do |t|
      t.string  :name
      t.integer :imageable_id
      t.string  :imageable_type
      t.timestamps
    end
  end
end

The problem with this approach is that imageable_type is a string (and by default it is 255 characters). This is a little ridiculous. For comparison, if we had a state machine with X states, would we describe the states with strings "State1", "State2", etc or would we just enumerate the state column and make it an integer? This gem will allow us to use an integer for the imageable_type column.

Installation

Add this line to your application's Gemfile:

gem 'polymorphic_integer_type'

And then execute:

$ bundle

Or install it yourself as:

$ gem install polymorphic_integer_type

For Rails 3.2 use version < 2. Version >= 2 has been tested on Rails 4.2 and Ruby 2.1

Usage

The gem is pretty straightforward to use.

First, include the extensions module and add the integer_type option to the associations that are going to be using this. (That way it will play nicely with polymorphic associations whose type you would rather leave as a string.)

class Picture < ActiveRecord::Base
  include PolymorphicIntegerType::Extensions
  belongs_to :imageable, polymorphic: true, integer_type: true
end
 
class Employee < ActiveRecord::Base
  include PolymorphicIntegerType::Extensions
  has_many :pictures, as: :imageable, integer_type: true
end
 
class Product < ActiveRecord::Base
  include PolymorphicIntegerType::Extensions
  has_many :pictures, as: :imageable, integer_type: true
end

Second, you need to create a mapping for the polymorphic associations. This should be loaded before the models. Putting it in an initializer is good (config/initializers/polymorphic_type_mapping.rb)

PolymorphicIntegerType::Mapping.configuration do |config|

  config.add :imageable, {1 => "Employee", 2 => "Product" }  	

end 

Note: The mapping here can start from whatever integer you wish, but I would advise not using 0. The reason being that if you had a new class, for instance Avatar, and also wanted to use this polymorphic association but forgot to include it in the mapping, it would effectively get to_i called on it and stored in the database. "Avatar".to_i == 0, so if your mapping included 0, this would create a weird bug.

If you want to convert a polymorphic association that is already a string, you'll need to set up a migration. (Assuming SQL for the time being, but this should be pretty straightforward.)

class PictureToPolymorphicIntegerType < ActiveRecord::Migration
  
  def up
    change_table :pictures do |t|
      t.integer :new_imageable_type
    end

    execute <<-SQL
      UPDATE reminders
      SET new_imageable_type = CASE imageable_type
                                 WHEN 'Employee' THEN 1
                                 WHEN 'Product' THEN 2
                               END
    SQL

    change_table :pictures, :bulk => true do |t|
      t.remove :imageable_type
      t.rename :new_imageable_type, :imageable_type
    end
  end

  def down
    change_table :pictures do |t|
      t.string :new_imageable_type
    end

    execute <<-SQL
      UPDATE picture
      SET new_imageable_type = CASE imageable_type
                                 WHEN 1 THEN 'Employee'
                                 WHEN 2 THEN 'Product'
                               END
    SQL

    change_table :pictures, :bulk => true do |t|
      t.remove :imageable_type
      t.rename :new_imageable_type, :imageable_type
    end
  end
end

Lastly, you will need to be careful of any place where you are doing raw SQL queries with the string (imageable_type = 'Employee'). They should use the integer instead.

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request