Page 265 - Asterisk™: The Future of Telephony

Database integration
Though immensely successful in the web development space for serving dynamic con-
tent, database integration has always been an underutilized possibility for driving
dynamic voice applications with Asterisk. Most Asterisk applications that do accom-
plish database integration outsource the complexity to a PHP or Perl AGI script because
the extensions.conf or AEL grammars are simply impractical for the level of sophisti-
cation required.

Adhearsion uses a database integration library, called ActiveRecord, developed by the
makers of the Ruby on Rails framework. With ActiveRecord, the end user seldom, if
ever, writes SQL statements. Instead, the developer accesses the database just like any
Ruby object. Because Ruby allows such flexible dynamism, access to the database looks
and feels quite natural. Additionally, ActiveRecord abstracts the differences between
database management systems, making your database access implementation agnostic.
Without going too much into the internals of ActiveRecord and more sophisticated
uses of it, let us consider the following simple MySQL schema:
CREATE TABLE groups (
`id` int(11) DEFAULT NULL auto_increment PRIMARY KEY,
`description` varchar(255) DEFAULT NULL,
`hourly_rate` decimal DEFAULT NULL
);
CREATE TABLE customers (
`id` int(11) DEFAULT NULL auto_increment PRIMARY KEY,
`name` varchar(255) DEFAULT NULL,
`phone_number` varchar(10) DEFAULT NULL,
`usage_this_month` int(11) DEFAULT 0,
`group_id` int(11) DEFAULT NULL
);
In practice we would obviously store much more information about the customer and
keep the service usage information in a database-driven call detail record, but this de-
gree of simplicity helps demonstrate ActiveRecord fundamentals more effectively.
To connect Adhearsion to this database, one simply specifies the database access in-
formation in a YAML configuration file like so:

adapter: mysql
host: localhost
database: adhearsion
username: root
password: pass
This tells Adhearsion how to connect to the database, but how we access information
in the tables depends on how we model our ActiveRecord objects. Since an object is
an instance of a class, we write a class definition to wrap around each table. We define
simple properties and relationships in the class with the superclass’s methods.
Here are two classes we may use with the aforementioned tables:

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