Getting Started

Add additional database connection config to database.yml.

# database.yml
production_user_001:
  adapter: mysql2
  username: user_writable
  host: db-user-001
production_user_002:
  adapter: mysql2
  username: user_writable
  host: db-user-002
production_user_003:
  adapter: mysql2
  username: user_writable
  host: db-user-003
production_user_004:
  adapter: mysql2
  username: user_writable
  host: db-user-004

Define cluster in initializers (e.g initializers/active_record_shard_for.rb)

ActiveRecord::ShardFor.configure do |config|
  config.define_cluster(:user) do |cluster|
    # unique identifier, connection name
    cluster.register(0, :production_user_001)
    cluster.register(1, :production_user_002)
    cluster.register(2, :production_user_003)
    cluster.register(3, :production_user_004)
  end
end

Include ActiveRecord::ShardFor::Model to your model class, specify cluster name and router name for the model, specify distkey which determines node to store.

class User < ActiveRecord::Base
  include ActiveRecord::ShardFor::Model
  use_cluster :user, :hash_modulo # hash_modulo is presented by this library.
  def_distkey :email
end

Use .get to retrive single record which is connected to proper database node. Use .put! to create new record to proper database node.

.all_shards returns each model class which is connected to proper database node. You can query with these models and aggregate result.

User.put!(email: '[email protected]', name: 'alice')

alice = User.get('[email protected]')
alice.age = 1
alice.save!

User.all_shards.flat_map {|m| m.find_by(name: 'alice') }.compact