Perl Virtual Database Module

Bastian Friedrich

   Collax GmbH

Edited by

Bastian Friedrich

   Copyright © 2007 Collax GmbH
     __________________________________________________________________

   Table of Contents

   1. Admin Guide

        1. Overview
        2. Dependencies

              2.1. Kamailio Modules
              2.2. External Libraries or Applications

        3. Parameters
        4. Functions

   2. Developer Guide

        1. Introduction
        2. Base class Kamailio::VDB
        3. Data types

              3.1. Kamailio::VDB::Value
              3.2. Kamailio::VDB::Pair
              3.3. Kamailio::VDB::ReqCond
              3.4. Kamailio::VDB::Column
              3.5. Kamailio::VDB::Result

        4. Adapters

              4.1. Function parameters

        5. VTabs

Chapter 1. Admin Guide

   Table of Contents

   1. Overview
   2. Dependencies

        2.1. Kamailio Modules
        2.2. External Libraries or Applications

   3. Parameters
   4. Functions

1. Overview

   The Perl Virtual Database (VDB) provides a virtualization framework for
   Kamailio's database access. It does not handle a particular database
   engine itself but lets the user relay database requests to arbitrary
   Perl functions.

   This module cannot be used "out of the box". The user has to supply
   functionality dedicated to the client module. See below for options.

   The module can be used in all current Kamailio modules that need
   database access. Relaying of insert, update, query and delete
   operations is supported.

   Modules can be configured to use the perlvdb module as database backend
   using the db_url_parameter:
modparam("acc", "db_url", "perlvdb:Kamailio::VDB::Adapter::AccountingSIPtrace")

   This configuration options tells acc module that it should use the
   perlvdb module which will in turn use the Perl class
   Kamailio::VDB::Adapter::AccountingSIPtrace to relay the database
   requests.

2. Dependencies

   2.1. Kamailio Modules
   2.2. External Libraries or Applications

2.1. Kamailio Modules

   The following modules must be loaded before this module:
     * perl -- Perl module

2.2. External Libraries or Applications

   The following libraries or applications must be installed before
   running Kamailio with this module loaded:
     * None (Besides the ones mentioned in the perl module documentation).

3. Parameters

   None.

4. Functions

   None.

Chapter 2. Developer Guide

   Table of Contents

   1. Introduction
   2. Base class Kamailio::VDB
   3. Data types

        3.1. Kamailio::VDB::Value
        3.2. Kamailio::VDB::Pair
        3.3. Kamailio::VDB::ReqCond
        3.4. Kamailio::VDB::Column
        3.5. Kamailio::VDB::Result

   4. Adapters

        4.1. Function parameters

   5. VTabs

1. Introduction

   Kamailio uses a database API for requests of numerous different types
   of data. Four primary operations are supported:
     * query
     * insert
     * update
     * delete

   This module relays these database requests to user implemented Perl
   functions.

2. Base class Kamailio::VDB

   A client module has to be configured to use the perlvdb module in
   conjunction with a Perl class to provide the functions. The configured
   class needs to inherit from the base class Kamailio::VDB.

   Derived classes have to implement the necessary functions "query",
   "insert", "update" and/or "delete". The client module specifies the
   necessary functions. To find out which functions are called from a
   module, its processes may be evaluated with the
   Kamailio::VDB::Adapter::Describe class which will log incoming requests
   (without actually providing any real functionality).

   While users can directly implement their desired functionality in a
   class derived from Kamailio::VDB, it is advisable to split the
   implementation into an Adapter that transforms the relational
   structured parameters into pure Perl function arguments, and add a
   virtual table (VTab) to provide the relaying to an underlying
   technology.

3. Data types

   3.1. Kamailio::VDB::Value
   3.2. Kamailio::VDB::Pair
   3.3. Kamailio::VDB::ReqCond
   3.4. Kamailio::VDB::Column
   3.5. Kamailio::VDB::Result

   Before introducing the higher level concepts of this module, the used
   datatypes will briefly be explained. The Kamailio Perl library includes
   some data types that have to be used in this module:

3.1. Kamailio::VDB::Value

   A value includes a data type flag and a value. Valid data types are
   DB_INT, DB_DOUBLE, DB_STRING, DB_STR, DB_DATETIME, DB_BLOB, DB_BITMAP.
   A new variable may be created with
my $val = new Kamailio::VDB::Value(DB_STRING, "foobar");

   Value objects contain the type() and data() methods to get or set the
   type and data attributes.

3.2. Kamailio::VDB::Pair

   The Pair class is derived from the Value class and additionally
   contains a column name (key). A new variable may be created with
my $pair = new Kamailio::VDB::Pair("foo", DB_STRING, "bar");

   where foo is the key and bar is the value. Additonally to the methods
   of the Value class, it contains a key() method to get or set the key
   attribute.

3.3. Kamailio::VDB::ReqCond

   The ReqCond class is used for select condition and is derived from the
   Pair class. It contains an addtional operator attribute. A new variable
   may be created with
my $cond = new Kamailio::VDB::ReqCond("foo", ">", DB_INT, 5);

   where foo is the key, "greater" is the operator and 5 is the value to
   compare. Additonally to the methods of the Pair class, it contains an
   op() method to get or set the operator attribute.

3.4. Kamailio::VDB::Column

   This class represents a column definition or database schema. It
   contains an array for the column names and an array for the column
   types. Both arrays need to have the same length. A new variable may be
   created with
my @types = { DB_INT, DB_STRING };
my @names = { "id", "vals" };
my $cols = new Kamailio::VDB::Column(\@types, \@names);

   The class contains the methods type() and name() to get or set the type
   and name arrays.

3.5. Kamailio::VDB::Result

   The Result class represents a query result. It contains a schema (class
   Column) and an array of rows, where each row is an array of Values. The
   object methods coldefs() and rows() may be used to get and set the
   object attributes.

4. Adapters

   4.1. Function parameters

   Adapters should be used to turn the relational structured database
   request into pure Perl function arguments. The alias_db function
   alias_db_lookup for example takes a user/host pair, and turns it into
   another user/host pair. The Alias adapter turns the ReqCond array into
   two separate scalars that are used as parameters for a VTab call.

   Adapter classes have to inherit from the Kamailio::VDB base class and
   may provide one or more functions with the names insert, update,
   replace, query and/or delete, depending on the module which is to be
   used with the adapter. While modules such as alias_db only require a
   query function, others -- such as siptrace -- depend on inserts only.

4.1. Function parameters

   The implemented functions need to deal with the correct data types. The
   parameter and return types are listed in this section.

   insert() is passed an array of Kamailio::VDB::Pair objects. It should
   return an integer value.

   replace() is passed an array of Kamailio::VDB::Pair objects. This
   function is currently not used by any publicly available modules. It
   should return an integer value.

   delete() is passed an array of Kamailio::VDB::ReqCond objects. It
   should return an integer value.

   update() is passed an array of Kamailio::VDB::ReqCond objects (which
   rows to update) and an array of Kamailio::VDB::Pair objects (new data).
   It should return an integer value.

   query() is passed an array of Kamailio::VDB::ReqCond objects (which
   rows to select), an array of strings (which column names to return) and
   a single string by which column to sort. It should return an object of
   type Kamailio::VDB::Result.

5. VTabs

   VTabs (virtual tables) provide a particular implementation for an
   adapter. The Alias adapter e.g. calls a function with two parameters
   (user, host) and expects a hash to be returned with the two elements
   username and domain, or undef (when no result is found). A sample VTab
   implementation for the Alias adapter demonstrates this technique with a
   Perl hash that contains the alias data.

   The standard Adapter/VTab pattern lets the user choose between three
   options on how to implement VTabs:
     * Single function. When a function is used as a virtual table, it is
       passed the operation name (insert, replace, update, query, delete)
       as its first parameter. The function may be implemented in the main
       namespace.

     * Package/class. The defined class needs to have an init() function.
       It will be called during the first call of that VTab. Addtionally,
       the package has to define the necessary functions insert, replace,
       update, delete and/or query. These functions will be called in a
       function context (first parameter is the class name).

     * Object. The defined class needs to have a new() function which will
       return a reference to the newly created object. This object needs
       to define the necessary functions insert, replace, update, delete
       and/or query. These functions will be called in a method context
       (first parameter is a reference to the object).
