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: 50 # total of 50 clients
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
=> 7873
bill2.unique_id
=> 7874
MedicalBill.find_by_unique_id(7873) # from DB shard for client_id = 1
=> #<MedicalBill id: 123, client_id: 1>
MedicalBill.find_by_unique_id(7874) # from DB shard for client_id = 2
=> #<MedicalBill id: 123, client_id: 2>

You can use the internal methods:

MedicalBill.unique_id_from(123, client_id: 1) # gives the unique_id
=> 7873
MedicalBill.id_from(7873) # gives the id
=> 123
MedicalBill.id_group_from(7874) # gives the client_id
=> { client_id: 2 }

You can specify multiple unique group attributes:

class MedicalBill < ActiveRecord::Base
  unique_by client_id: 50, client_part: 5 # total of 50 clients and 5 parts
end

Multiple tables example

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

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

You can supply both group attributes and a block, and the block can also return more than one field:

class MedicalBill < ActiveRecord::Base
  unique_by(client_id: 50, client_part: 5, xy: 10, halfz: 20) do
    { xy: self.x * self.y, halfz: self.z / 2 }
  end
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

See also

After adding the unique groups to the id, the unique_id might turn out pretty large. You could use rebase_attr to fix that:

class MedicalBill < ActiveRecord::Base
  unique_by client_id: 500
  rebase_attr :unique_id, to: 32, readable: true
end

bill = MedicalBill.find(3528918) # from a DB shard for client_id = 1
bill.unique_id
=> "ywr3bxx"
MedicalBill.find_by_unique_id(MedicalBill.decode_unique_id("ywr3bxx"))
=> #<MedicalBill id: 3528918, client_id: 1>

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