= activerecord_snapshot_view

activerecord_snapshot_view provides simple management of snapshot materialized views for ActiveRecord

a snapshot view is created by includeing the <tt>ActiveRecord::SnapshotView</tt> module into an ActiveRecord
class. new versions of the snapshot are created using the <tt>new_version</tt> class method

multiple versions of the view are maintained : there is
a single active version, a working version, and one or more history tables [by default 1]

the model's +table_name+ method is overwritten to reflect the active table, so all ActiveRecord
model methods, like finders, work transparently. the caveat is that you must use the +table_name+ method
to determine the current snapshot's table name when constructing SQL

to use, <tt>include ActiveRecord::SnapshotView</tt> into your model :

  class Foo < ActiveRecord::Base
    include ActiveRecord::SnapshotView
  end

there are class methods to get the different table names, and manipulate the version :

* <tt>Foo.table_name</tt> : current active or working table name
* <tt>Foo.working_table_name</tt> : current working table name
* <tt>Foo.active_table_name</tt> : current active table name
* <tt>Foo.new_version(&block)</tt> : run +block+ to create a new version of the table
* <tt>Foo.updated_version(&block)</tt> : copy all data from the active table to the working table, then run +block+ to update the working version

during the execution of +block+ in +new_version+ or +updated_version+ <tt>Foo.table_name</tt> returns the working table name. if +block+ completes without raising an exception, or if the exception is an ActiveRecord::SnapshotView::SaveWork, then the working table becomes permanently globally active

the active table name is maintained as a row in an automatically created auxilliary table, 
[<tt>foos_switch</tt> in the case of <tt>Foo</tt>], and this is updated in a transaction

the presence of the historical tables [which are recycled] means that even though a transaction
may advance_version, other transactions already in progress will continue to see the old 
active table_name, and selects in progress will continue to completion without rollback [ provided
they don't take longer to complete than it takes to recycle all history tables ]

== Dependencies

MySQL only at the moment

== Note on Patches/Pull Requests
 
* Fork the project.
* Make your feature addition or bug fix.
* Add tests for it. This is important so I don't break it in a
  future version unintentionally.
* Commit, do not mess with rakefile, version, or history.
  (if you want to have your own version, that is fine but
  bump version in a commit by itself I can ignore when I pull)
* Send me a pull request. Bonus points for topic branches.

== Copyright

Copyright (c) 2009 mccraig mccraig of the clan mccraig. See LICENSE for details.