== amee-data-persistence

The amee-data-persistence gem provides database support for use in conjunction
with the amee-data-abstraction gem.

Licensed under the BSD 3-Clause license (See LICENSE.txt for details)

Authors: James Hetherington, James Smith, Andrew Berkeley, George Palmer

Copyright: Copyright (c) 2011 AMEE UK Ltd

Homepage: http://github.com/AMEE/amee-data-persistence

Documentation: http://rubydoc.info/gems/amee-data-persistence
== INSTALLATION

 gem install amee-data-persistence
 
== REQUIREMENTS

 * ruby 1.8.7
 * rubygems >= 1.5

 All gem requirements should be installed as part of the rubygems installation process 
 above, but are listed here for completeness.

 * amee-data-abstraction ~> 1.0.0
 
== USAGE

The library repesents calculations as
database records using two classes (<i>AMEE::Db::Calculation</i> and
<i>AMEE::Db::Term</i>) both of which inherit <i>ActiveRecord::Base</i>.

The library also defines the <i>AMEE::DataAbstraction::PersistenceSupport</i>
module which is mixed into the <i>AMEE::DataAbstraction::OngoingCalculation</i>
class by default when the library is required. The module provides a number of
class and instance methods which provide an interface between the
<i>AMEE::DataAbstraction::OngoingCalculation</i> class (and its instances) and
the database. It is via these methods that the persistence functionality
provided by the <i>AMEE::Db</i> classes is principally used.

The level of data storage can be configured to three distinct levels, representing
the range of calculation terms which are persisted: all; outputs and metadata only;
and metadata only.

The global persistence storage level and migrations for the database tables
(under /db/migrate) can be generated using the command line generator command:

  $ rails generate persistence <storage_level>

where <storage_level> can be either 'everything', 'outputs' or 'metadata', e.g.,

  $ rails generate persistence everything


=== Example usage

  my_calculation = OngoingCalculation.find(:first)

                                 #=> <AMEE::DataAbstraction::OngoingCalculation ... >

  my_calculation = OngoingCalculation.find(28)

                                 #=> <AMEE::DataAbstraction::OngoingCalculation ... >

  my_calculation = OngoingCalculation.find(:all)

                                 #=> <AMEE::DataAbstraction::CalculationCollection ... >

  my_calculation = OngoingCalculation.find_by_type(:all, :electricity)

                                 #=> <AMEE::DataAbstraction::CalculationCollection ... >

  my_calculation.id              #= 28

  my_calculation.db_calculation  #=> <AMEE::Db::Calculation ... >

  my_calculation.to_hash         #=> { :profile_uid => "EYR758EY36WY",
                                       :profile_item_uid => "W83URT48DY3W",
                                       :type => { :value => 'car' },
                                       :distance => { :value => 1600,
                                                      :unit => <Quantify::Unit::SI> },
                                       :co2 => { :value => 234.1,
                                                 :unit => <Quantify::Unit::NonSI> }}

  my_calculation.save            #=> true

  my_calculation.delete          #=> nil