|Perl Monk, Perl Meditation|
Re: When to use ORMs, Catalyst, etcby philcrow (Priest)
|on Jul 12, 2007 at 20:16 UTC||Need Help??|
Since you asked, here is the answer we provide for the Gantry framework in Gantry::Docs::Why. It applies to any framework.
Do It Yourself
Once upon a time, I had a computer savvy friend with an unorthodox opinion. He hated the idea of using an SQL database, unless the amount of data or the frequency of accessing it justified its use solely on the basis of run time performance. "Why not roll your own?" was his continual question. After all, he reasoned, a small application probably has only a small amount of data which can be easily described. Therefore, a flat file scheme is sufficient for almost all apps.
For the moment, set aside the problems of scalability. That is, ignore for the moment the valid point that the complexity of apps tends to grow as they age and that more and more users come from the woodwork to use successful apps.
The argument against databases falls on its own, just based on developer efficiency. If you have your data in a hand written scheme I have a hurdle to clear before I can work on your app. With an SQL database, I can use standard tools to explain your data layout. This leads quickly to an understanding of the app itself (as the famous quote about sharing and concealing flowcharts so well states).
So, there is an important lesson to be learned from SQL databases. Even when they make no sense in terms of throughput during app execution, they still make a great deal of sense in a typical shop. They create a lingua franca for describing data. That common language, by itself, is a great help to developers.
No matter what a web application does, it shares an obvious trait with all other web apps: the web. Users will interact with our web apps through their browsers. The details of the interaction may differ depending on whether we use mod_perl, CGI, or something else, but the fact remains that all the data coming into and out of our apps travels in http requests.
This leads naturally to a common set of problems and benefits for all web apps. When we notice that programs have things in common, we should immediately begin thinking of code they can share. Factoring out the common code will save us development time. If we factor out enough behavior, we can call it a framework. If other people use our framework it can become a lingua franca at least among our friends and colleagues.
The following section describes one of the most common web app features.
Typical Web Apps
Though there is some variation in what web applications do (we have some that provision cable modems) they are primarily occupied with the same basic task. They manage data in an SQL database. This leads to a small number of common tasks that each app must perform. In fact, most apps have multiple database tables to manage, so they perform these common tasks repeatedly.
Consider a typical work flow. A user comes to a customer facing web site to update their address. From a generic front page, they choose a link to the app which updates the relevant data. On that app, they log in (providing account name or number and a password or two). Once authenticated, they choose a navigation tab or link which displays an address form with their current information. The user then updates the relevant bits and presses submit. The site validates data (shunting the user back to the page with error messages on failure) and updates it in the underlying SQL table. Finally, the site takes them back to some reasonable page, like their account home.
Our company does not allow users to update their address as described above, since we are a wire line data provider (cable TV, telephone, internet). Yet, the outline above is exactly correct for a large number of the pieces in almost all of our apps. Here are the steps in summary:
Now, there may be substantial additional work to be done in concert with step 4 (like configuring those cable modems or sending spam to the marketing department). And there may be other activities, like report generation (but that may really be a special case of the above). Yet, for all the special things that a particular application needs to do, the five steps above are repeated by multiple pieces of almost all apps.
Programmers are (or should be) lazy. We don't want to continually recode the above. Not only is that tedious, but it suffers from the same problems that rolling our own data scheme for each app would. It makes for lots of apps which are almost the same, to the point that the details which differ are hard to deduce. Further, newly hired programmers face a number of hurdles to understanding a bunch of separately coded apps.
So, we want a lingua franca for web applications in the same way that we wanted SQL for database access. The problems of a web app are more numerous and more disparate, so the solution is more complex. But, a web framework is a lingua franca for web apps.
There are many web app frameworks in the wild these days. I'll not even bother to start a list of them. Suffice it to say, if you find one that will work for you and your shop, it will save you development time. And, it will provide an easier path for those new to your shop. If it happens to be wildly popular, you might even be able to hire people already familiar with it.
In our shop we go one step further. Since database backed web apps are so similar, we developed a language for describing them called Bigtop. By describing an app in Bigtop syntax, we can generate and regenerate its repetitive bits. This leaves us free to work on the more interesting bits.
In summary, if you code more than one app of a type, you owe it to yourselves to factor out the common parts into some sort of framework. Using a framework already on CPAN gives you others to help you with both your individual apps and with the framework internals. It's much easier to come up to speed on a public framework, for which there are tutorials on line, talks at conferences, getting started movies, and more, than it is to pick up a framework that was created in a single shop and never given the documentation (and code review) which are the inevitable result of external users.
Please don't think this is only a shameless plug for Gantry. (It is that, of coures.) These benefits come from having groups of users in more than one setting.Phil
The Gantry Web Framework Book is now available.