Part of the AMEEappkit, this gem provides a data abstraction layer, decreasing the amount and detail of development required to build AMEEapps
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== amee-data-abstraction

The amee-data-abstraction gem provides an easy-to-use, highly configurable interface
for providing AMEE-driven calculations to Rails applications.

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




 gem install amee-data-abstraction


 * 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 ~> 4.1
 * uuidtools = 2.1.2
 * quantify = 2.0.0

The library provides several useful functions:

1. Abstracts away most of the details for making API calls into an elegant DSL-style

2. Provides a host of macro-style helper methods for rapidly generating
calcualtion templates

3. Models each type of AMEE calculation as a fully configurable Ruby object.

4. Enables the configuring of which inputs (drills and profile item values) and
outputs (return values) to handle and display for each calculation type.

5. Enables configuration of default interfaces (select lists, text fields, etc.)
for calculation components.

6. Enables customised, human-readable names and other descriptors to be associated
with calculations or calculation components (inputs, outputs, etc.).

7. Enables arbitrary metadata to be associated with calculations.

8. Provides support for handling alternative units, including full configurability.

=== Brief introduction

The calculations provided by AMEE categories are represented by instances of the
class AMEE::DataAbstraction::Calculation.

This class has two subclasses, (1) PrototypeCalculation, which is used to
represent a blank calculation template for a particular type of calculation; and
(2) OngoingCalculation, instances of which represent actual individual calculations
which are made.

Calculation objects contain instances of the AMEE::DataAbstraction::Term class.
The Term class, and its subclasses Input, Drill, Profile, Metadatum, Usage, and
Output, represent components of a calculation such as inputs, outputs (i.e.
caluclated values) and arbitrary metadatum.

Prototype calculations can be contained within an instance of the class
AMEE::DataAbstraction::CalculationSet, in order to provide rapid access to any
defined calculation templates and instantiating of a new instance of a real

=== Example usage

Configure a calculation

  include AMEE::DataAbstraction

  my_template_calculation = {

    label :electricity                         # Custom unique label
    name "Grid electricity supply"             # Custom name
    path "/some/path/in/the/amee/platform"     # AMEE platform category path
    terms_from_amee                            # helper for initializing and
                                                 configuring all calculation
                                                 terms based on AMEE platform

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

Create a new calculation instance

  my_calculation = my_template_calculation.begin_calculation

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

Set the calculation inputs

  params = { :country => 'Sweden',
             :consumption => { :value => 6000, :unit => 'kWh' }}

  my_calculation.choose! params

Submit to AMEE for calculation


  my_calculation[:co2].to_s     #=> "2456 kg"

=== Configuring mutliple application calculation prototypes

Typical practice is initialize the calculation prototypes required for an
application via a configuration file which creates the required calculation
templates within an instance of CalculationSet. Such a configuration file can
be structured the follow DSL:

  # e.g. /config/calculations/my_emissions_calculations.rb

    calculation {
      label :electricity
      name "Grid Electricity Supply"
      path "/some/electricity/associated/path/in/amee"

    calculation {
      label :transport
      name "Employee Commuting"
      path "/some/transport/associated/path/in/amee"

    calculation {
      label :fuel
      name "Fuel Consumption"
      path "/some/fuel/associated/path/in/amee"

The default location for such files within Rails applications is under
/config/calculations. If such an approach is taken, the configuration can be
read and a calculation set generated by using the filename, thus:


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

Otherwise, the path to the configuration file can be provided:


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

The calculation set is accessible as follow using the same argument as used
by the Find method (filename if conventional Rails location, path otherwise):


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

From this global calculation set, initialize a new calculation

  my_fuel_calculation = CalculationSet.sets['my_emissions_calcualtions'][:fuel].begin_calculation

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

  a_different_transport_calculation = CalculationSet.sets['my_emissions_calcualtions'][:transport].begin_calculation

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

=== Locking the calculation configuration
Depending on the nature of the configuration file(s) used a call to the AMEE platform may be required in order to retrieve all of the information required to represent the specified calculations. This might be the case for example, when using the terms_from_amee and similar convenience methods: details such as term names, paths, units and default values are collected from the platform once at start up. In order to avoid this call every time an application is started, a .lock file can be generated which contains a complete description of the configuration information. To generate lock files use:

    rake amee:calculations:lock[<filename>]

    rake amee:calculations:lock_all

=== Configuring a connection to AMEE

The AMEE::DataAbstraction module uses the 'amee' ruby gem to interact with AMEE.
The standard method for configuring and instantiating a connection to the AMEE
API is to provide authentication credentials in the /config/amee.yml file.  It is
recommended to use one of the caching options in order to reduce API calls:

    username: <some user name>
    password: <some password>
    cache: rails

    username: <some user name>
    password: <some password>
    cache: rails

    username: <some user name>
    password: <some password>