[seul-edu] test programming before you begin database design :-)

[mike eschman <meschman@engima.com>]

Faking It - Simulated Database Queries @
http://www.phpbuilder.com/columns/richmond20020827.php

How often have you put off coding part of an application because the
database wasn't ready?

If you answered even once, you delayed a project -- which means you
delayed your client. Maybe it was only a couple of days, maybe it
was a couple of weeks. In either case, it took you a little longer
to finish and your client had to wait. And we all know how patiently
clients wait.

But what if you don't wait for your DBA? What if you just... pretend
the database is done... and start coding? You could get finished on
schedule.   Or maybe even ahead of schedule. Now, if the application
would just play along, if it would just fake it while you code...
Playing Along

Query simulations (QuerySims) were conceived by Hal Helms to remove
the design and population of a database from the critical path of
application development. Using QuerySims a programmer may proceed
with writing and testing data display code while the DBA is
designing the database, saving a significant amount of time.

Alternatively, the database may be designed after the application is
finished.  I've worked on more than one project were columns and
even whole tables were never even used. It sounds counter intuitive
to the way most of us learned to develop applications but by waiting
we know exactly what columns and tables are needed and how best to
group them for performance on the database end.

When the database is complete, simply change the connect string to
point to the real database and replace the QuerySim text with an SQL
select statement that returns the appropriate columns. There is no
need to modify your display code, because as far it could tell, it
was already using a result set from the database.

QuerySims are especially useful when following the FLiP methodology
and using the Fusebox framework for application development, but you
don't have to be using FLiP or Fusebox to use QuerySims!
Database Abstraction

Keeping your code portable from one database to another will
increase its reusability tremendously, but this is virtually
impossible using PHP's native database functions. The intelligent
thing to do is to use a database abstraction layer that can
interface with any database using common methods.  Even more
intelligent is to use one that is already familiar to other
developers, so when your code needs to be updated by your successor,
he or she doesn't need to learn a new API in addition to the ins and
outs of your application. (Remember this works both ways, things
will be easier for you if the situation is reversed.)

The original QuerySim was a ColdFusion custom tag that took
advantage of ColdFusion's built in database abstraction layer and
functions for populating a real query-scoped variable with data.
Unfortunately, PHP doesn't have a built in abstraction layer we can
populate with data. Since each database has its own set of functions
for connecting, querying and manipulating data, we need a common
interface for a clean switch from QuerySim to a live database.

There are several very good database abstraction layers available,
PEAR DB and ADODB are two of the more popular ones. This version of
QuerySim is implemented as a database driver for PEAR DB.
PEAR DB

DB is a class package available from the PHP Extension and Add-on
Repository (PEAR) project. Sean Cazzell's article will give you a
quick synopsis of what PEAR is trying to achieve.

If you would like to follow along with the tutorial, you may
download the current stable DB package here . But one of PEAR's
strengths is its close association with the PHP Group; PEAR and the
DB package are included with the default PHP install, so you
probably already have it!