SingleWriteMultiRead
====================

This plugin is designed to allow an application to use many read slave DBs with a single write DB.  Active record finder methods are rewritten to use a random slave, and all save methods are rewritten to write to the single master.

Using the plugin is simple.  First you must define the slave databases in database.yml.  Any and all definitions that include the word 'slave' in their definition will be used as a read slave in the production environment (For example: read_slave, read_slave_1, slave_db, etc.).  The database defined as 'production' will be used as the write master.  To use a slave in another environment, include the name of the environment somewhere in the name of the database definition.  For example, to use a read slave in the development environment, you could use a name like read_slave_development.

Here is an example for a production environment read slave:

read_slave_1:
  adapter: mysql
  database: slave_1
  username: webapp
  password: agaerfa3191
  encoding: utf8
  host: 74.125.45.100

Once you have defined your connections in database.yml, simply add the following line to your model definitions for any ActiveRecord model that you want to have use the read slave:

single_write_multi_read

After that, all finds will use a random slave for reads and the production database as the write master.  Calculation class methods (count, maximum, average, etc..) will also use the read slaves.

*NOTE* The class of the object returned by any find will include the slave connection name.  For example, say you have a class 'Person' implementing single_write_multi_read, with a slave database definition called read_slave_1 defined in database.yml.

p = Person.find(:first) #Returns a person object retrieved from a random slave (in this case read_slave_1)

Calling class on this object returns a class name with the slave module included in the namespace.

p.class 				#Returns the class name including the readslave name
>> ReadSlave1::Person


Calling class on an object returned by this slave will return ReadSlave1::Person as the class.  To get the actual class, call the class method 'real_class' instead.

p.real_class			#Returns the actual class without the read slave module
>> Person

Copyright (c) 2008 Daniel Lockhart, released under the MIT license