unique_by

This simple gem allows specifying uniqueness groups for an attribute, giving you something to expose to the outside world.

When do you need this?

• If you're sharding your database.
• If you have multiple tables that you want to expose a unique ID for.

Installation

Add this line to your application's Gemfile:

gem 'unique_by'

And then execute:

$ bundle

Or install it yourself as:

$ gem install unique_by

Usage

Sharding example

You first need to specify a unique group in your model:

# == Schema Info
#
# Table name: medical_bills
#
#  id                  :integer(11)    not null, primary key
#  client_id           :integer(11)
#

class MedicalBill < ActiveRecord::Base
  unique_by :client_id, total: 50
end

then, you can use these basic methods:

bill1 = MedicalBill.find(123) # from a DB shard for client_id = 1
bill2 = MedicalBill.find(123) # from a DB shard for client_id = 2

bill1.unique_id
=> "62p"
bill2.unique_id
=> "62q"
MedicalBill.find_by_unique_id("62p") # from DB shard for client_id = 1
=> #<MedicalBill id: 123, client_id: 1>
MedicalBill.find_by_unique_id("62q") # from DB shard for client_id = 2
=> #<MedicalBill id: 123, client_id: 2>

You can use the internal methods:

MedicalBill.unique_id_from(1, 123) # gives the unique_id from client_id, id
=> "62p"
MedicalBill.id_from("62p") # gives the id
=> 123
MedicalBill.id_group_from("62q") # gives the client_id
=> 2

And use bits instead of total:

class MedicalBill < ActiveRecord::Base
  unique_by :client_id, bits: 6 # equivalent to total: 64
end

You can specify multiple unique group attributes:

class MedicalBill < ActiveRecord::Base
  unique_by :client_id, :client_part, total: [50, 5]
end

Multiple tables example

You can supply a block to give your own mechanism for determining the group:

class MedicalBill < ActiveRecord::Base
  unique_by(total: 2) { 1 }
end
class UtilityBill < ActiveRecord::Base
  unique_by(total: 2) { 2 }
end

You can supply both group attributes and a block, and the block can also return an array:

class MedicalBill < ActiveRecord::Base
  unique(:client_id, :client_part, total: [50, 5, 10, 20]) { [self.x * self.y, self.z / 2] }
end

Not ActiveRecord

The generator module is already included in ActiveRecord::Base, but if you want the above methods in another class you can extend it:

class MyClass
  extend UniqueBy::Generator

  def self.primary_key
    :id # or 'id'
  end
end

Contributing

1. Fork it ( https://github.com/odedniv/unique_by/fork )
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 a new Pull Request