I see. So you're volunteering to go through and modify all the 600+ DBD::* modules; and all the modules that use them; and all the code written in the last 15 years that use them; just so that you can provide introspection of things that nobody will ever want to introspect?

Is this really what you think I was suggesting? Or do you actually understand the context within which my previous post was made?

Let's just pretend for a moment that we could re-write history, and DBI had specified that the first parameter to DBI was a hashref.

Ah, it appears you do. I guess that first paragraph was just for "flavor," eh?

You would have a hash rather than a string. That would make it easier to wrapover in your DSN object--though this parsing you speak of is hardly onerous. But then, as now, that wrapover is pointless.

First, in my hypothetical version of DBI, I'd standardize the common names in the hash. For example, if you have something like a database, use the "database" key (not "db", not "dbname", etc.), use "host" for the host (not "hostname", not "server", etc.), and so on. This would be a documented part of DBI. Standardized names would cover at least half of the things commonly specified in DSNs.

Second, I think you still don't understand what Rose::DB actually does. Providing a nicer interface to DSNs is not its primary, or even secondary purpose. Even if it simply passed the registered data source information straight through to DBI, its most important roles would remain unchanged: first and foremost, to provide a uniform interface for database-specific behaviors to Rose::DB::Object; and second, as a registry of logically named data sources, organized in a generic two-level hierarchy (domain and type) with an optional file-based configuration overlay to allow sensitive information such as production passwords to be kept out of the source code, while still using exactly the same code in development and production.

To clarify that first role, the goal is to keep code out of Rose::DB::Object that says "if the database is mysql, do X, else if the database is oracle, do Y, else ..." and so on. (That goal is about 99% achieved; there are a few stragglers.) Instead, such behavior is delegated to the current Rose::DB-derived object, which is an object attribute in Rose::DB::Object (i.e., each Rose::DB::Object-derived object "has a" Rose::DB-derived object in its "db" attribute). This arrangements allows a Rose::DB::Object-derived object to, say, be loaded from one database and then stored into another, even if the two databases use a different server product, as shown in the tutorial. Assume "production" is PostgreSQL and "archive" is MySQL:

# My::DB "isa" Rose::DB
$production_db = My::DB->new('production'); # PostgreSQL
$archive_db    = My::DB->new('archive');    # MySQL

# Load bike from production database
$p = Product->new(name => 'Bike', db => $production_db);
$p->load;

# Save the bike into the archive database
$p->db($archive_db);
$p->insert;

# Delete the bike from the production database
$p->db($production_db);
$p->delete;

[download]

Again, understand that the Rose::DB::Object-derived Product object calls back into its Rose::DB-derived My::DB object whenever it does anything that might vary from one database to another. I hope you'll agree that Rose::DB is just a bit more than a "DSN object."

So, even if we could ignore history, and turn back the clock to do things your way, there'd be no value in it.

There'd be considerable value in that people could use DBI without constantly having to run "perldoc DBD::Whatever" to look up the driver-specific DSN syntax that they don't remember off the top of their head. There's also the added efficiency of not having to parse a string inside the DBD (and not having to write string parsing code in C, as it often is today), and being able to add new attributes without worrying if there's "room" in the current DSN syntax or having to make a second or third syntax, as many DBD::* modules have done, to accomodate new/different parameters. Finally, since a serialized format does actually have its uses (e.g., when stored in a file or sent over a network connection), DBI could support one or more of the standard formats that can be used to serialize a Perl hash into a string: JSON, YAML, Data::Dumper, etc.

In reply to Re^8: Avoiding compound data in software and system design by siracusa
in thread Avoiding compound data in software and system design by metaperl

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