sqlLayer, pushing foomatic data into the database

The second portion of my project is to write a perl lib to push foomatic’s data into a relational database. This would allow the use of SQLite instead of the xml database for foomatic-db-engine. This isn’t going to affect CUPS users (the vast majority of people) since last year’s project (vitor’s) created pyppd which can side-step foomatic-db-engine entierly for end users. What it does though is provide considerable performance increases for users of legacy spoolers.

Like with xmlParse I am not treading new ground, openprinting already has a script to import the data set. This script was written as part of another GSoC project two years ago as part of the openprinting website re-design. A few months before this year’s GSoC Till gave me a copy of the script along with a database dump. I was able to convert this database dump into a sqlite database. With those I’ve been able to make considerable progress. Currently I’m adding support for about one table a day.

Thinking about the project as a whole I am rather proud of the phonebooks, by extending them to document the database schema I’ve been able to operate at a fairly high abstraction level. Whereas the C programs and the PHP import script had 100s of lines of simple ‘if def assign’ the phonebooks let a single* loop handle all the simple renaming and processing for xmlParse. For complex types the raw data is handed to special case code to process.

Sample special case code for option’s complex data:
#The specific groups
} elsif ($group == 11) { #constraints
	setConstraint($node, \$perlData{$destinationKey});

} elsif ($group == 12) { #enum_values
	foreach my $subnode ($node->findnodes("./enum_val")) {
		my %enumValue;

		foreach my $subsubnode ($subnode->findnodes('./@id[1]')) {
			$enumValue{"idx"} = $subsubnode->to_literal;
		}

		foreach my $longnames ($subnode->findnodes('./ev_longname')) {
			$this->setHumanReadableText(\%enumValue,\"comment", $longnames);
		}

If I were to redo my work I would make the phonebooks document the structures of the complex data. This would allow an even further generalisation and do away with the special case code for the complex types.

That isn’t going to happen though, the current code has been tested and is working. And while the special cases could have been done better I do realise that a more general approach would have had a much harder time conforming to the behaviour of the C programs.

 

*Not necessarily a single instance of the loop. I’m a bit ashamed to admit but there are actually three copies of the same loop, one for each xml type. It is this way because when I created the phonebooks I made groups above 10 be namespace specific groups. Thus group 11 for an option xml is different from printer’s group 11. In xmlParse this is implemented by the fact that the option loop is separate from the printer’s loop. The groups that all loops share are in a separate function, so really only the loop structure is copy pasted. In sqlLayer I’ve kept the loop singular and simply added support for namespaces, support which will be made cleaner if I can think of a way.

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