This gem provides master and slave databases support for Rails applications. It maintains a slave database configuration in config/shards.yml, and treats config/database.yml as master database. Then, you can choose which database you want to use in your ActiveRecord::Relation clauses.

For example, you can use slave database to execute complicated and time-consuming database queries to balance the performance of master database, or separate read and write database operations.

• Ruby >= 2.0.0
• Rails >= 3.2.x

Put the following line into you Gemfile:

gem 'database_slave', '>= 0.1.0'

then execute:

bundle install

1. First of all, create a file named shards.yml in your Rails config directory, its content is very similar to config/database.yml:

development:
  slave_database1:
    adapter: mysql2
    encoding: utf8
    reconnect: false
    port : 3306
    pool: 5
    username: root
    password: test
    host: 127.0.0.1
    database: books

  slave_database2:
    adapter: mysql2
    ...
    ...
test:
  slave_database1:
    ...
production:
  slave_database1:
    ...

2. Then add following to your settings.yml file:

using_slave: true

true means you can use slave database, false means not.

There are two ways to use slave database:

1. Single Use: Append using_slave(:slave_database_name) to each ActiveRecord::Relation clause.

Example:

Book.where(id: 5).using_slave(:books_slave_database)

2. With Block: In this way, all of queries in the block will use slave_database to execute queries. With this you don't need to append using_slave() to each queries.

Example:

Book.using_slave(:books_slave_database) do
  books1 = Book.where(id: 9)
  books2 = Book.where('id > 100')
end

Because of alias, you can use using instead of using_slave.

See LICENSE file.