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Chapter 15: Relational Database Integration
Troubleshooting Database Issues
When working with ODBC database connections and Asterisk, it is important to
remember that the ODBC connection abstracts some of the information passed
between Asterisk and the database. In cases where things are not working as
expected, you may need to enable logging on your database platform to see what
Asterisk is sending to the database (e.g., which SELECT, INSERT, or UPDATE statements
are being triggered from Asterisk), what the database is seeing, and why the database
may be rejecting the statements.
For example, one of the most common problems found with ODBC database integra‐
tion is an incorrectly defined table or a missing column that Asterisk expects to exist.
While great strides have been made in the form of adaptive modules, not all parts of
Asterisk are adaptive. In the case of ODBC voicemail storage, you may have missed a
column such as flag, which is a new column not found in versions of Asterisk prior
to 11.1 As noted, in order to debug why your data is not being written to the database
as expected, you should enable statement logging on the database side, and then
determine what statement is being executed and why the database is rejecting it.
SQL Injection
Security is always a consideration when you are building networked applications, and
database security is no exception.
In the case of Asterisk, you have to think about what input you are accepting from
users (typically what they are able to submit to the dialplan), and work to sanitize that
input to ensure you are only allowing characters that are valid to your application. As
an example, a typical telephone call would only allow digits as input (and possibly the
* and # characters), so there would be no reason to accept any other characters. Bear
in mind that the SIP protocol allows more than just numbers as part of an address, so
don’t assume that somebody attempting to compromise your system is limited to just
digits.
A little extra time spent sanitizing your allowed input will improve the security of
your application.
Powering Your Dialplan with func_odbc
The func_odbc dialplan function module allows you to define and use relatively sim‐
ple functions in your dialplan that will retrieve information from databases as calls
are being processed. There are all kinds of ways in which this might be used, such as
1 This was actually an issue one of the authors had while working on this book, and he found the flag column
by looking at the statement logging during testing.
Powering Your Dialplan with func_odbc
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managing users or allowing the sharing of dynamic information within a clustered set
of Asterisk machines. We won’t claim that this will make designing and writing dia‐
lplan code easier, but we will promise that it will allow you to add a whole new level
of power to your dialplans, especially if you are comfortable working with databases.
We don’t know anybody in the Asterisk community who does not love func_odbc.
The way func_odbc works is by allowing you to define SQL queries, to which you
assign function names. The func_odbc.conf file is where you specify the relationships
between the functions you create and the SQL statements you wish them to perform.
You use the named functions you have created in your dialplan to retrieve and update
values in the database.
In order to get you into the right frame of mind for what follows, we want you to
picture a Dagwood sandwich.2
Can you relay the total experience of such a thing by showing someone a picture of a
tomato, or by waving a slice of cheese about? Hardly. That is the conundrum we faced
when trying to give useful examples of why func_odbc is so powerful. So, we decided
to build the whole sandwich for you. It’s quite a mouthful, but after a few bites of this,
peanut butter and jelly is never going to be the same.
ODBC Configuration File Relationships
Several files must all line up in order for Asterisk to be able to use
ODBC from the dialplan. Figure 15-1 attempts to convey this visu‐
ally. You will probably find this diagram more helpful once you
have worked through the examples in the following sections.
2 And if you don’t know what a Dagwood is, that’s what Wikipedia is for. I am not that old.
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Chapter 15: Relational Database Integration
Figure 15-1. Relationships between func_odbc.conf, res_odbc.conf, /etc/odbc.ini (uni‐
xODBC), and the database connection
A Gentle Introduction to func_odbc
Before we dive into func_odbc, we feel a wee bit of history is in order.
The very first use of func_odbc, which occurred while its author was still writing it, is
also a good introduction to its use. A customer of one of the module’s authors noted
that some people calling into his switch had figured out a way to make free calls with
his system. While his eventual intent was to change his dialplan to avoid those prob‐