For example, say you have data about a bunch of people. You know their name, their age, and their hair color. You create a simple Perl object to hold this data, and you can instantiate it at will:

    my $me = new Person;
    $me->age(22);
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Now, what if you want to make these objects persistent? In other words, between runs of your program, you need to store this data somewhere. A database is as good a place as any.

The problem, though, is that placing your database code into your object (into a save method, for example) would make your code very specific. Objects should be more flexible about how they're stored--they shouldn't be tied in to only one storage method.

This is where Tangram comes in: it provides the methods that let you store your object in a database. So you can create it, store it, quit your program, then start it up again--and load your object from the database magically, as if it had never left.

So it's not a matter of you being forced/cajoled/etc. into writing object-oriented code. The point here is that you're *already* writing OO code, and now you need a way to store your objects. You need object persistence, and that's what Tangram gives you.

I've never used it myself, though. :)

Let me see if I got this straight...

Suppose I have an online store where I sell goods to several different countries each using its own currency. I could say (for Brazil's case):

my $real = new Currency;
$real->name('Real');
$real->country('BR');
$real->dolarValue(1.81);
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And repeat this as many times necessary for each country. Then use set everything up, and use DBI to get the items from a shopping cart as usual (name, price, other attributes). Then my app would work as if my currency variables had been declared at startup, so I wouldn't have to do a 'select' myself to find out what the price of an item was in Reals?

That's a bit confusing... Let me try this instead.
Instead of doing two selects (one for the product, and one for the currency), I could have the currency loaded as an object and do my select on the product as if the currency information had always been there?

#!/home/bbq/bin/perl
# Trust no1!

Well... I'm not sure I know quite what you mean. In your example, you could create all of those Currency objects, then use Tangram to insert them into a database. That would be one script.

Then, in another script, you could tell Tangram to go and get you a particular Currency object. It would load the data from the database and hand you back a Currency object, just like the one you had created in the first script.

You're not actually eliminating select statements, because *someone* still has to do a select--even if it's not you, it's Tangram. :) But you don't have to worry about that select; you can just act as if you had created the Currency object in the same script.

Does that make sense?

There's a good introduction to using Tangram in WebTechniques.