twenty four merry days of Perl Feed

Making a list, checking it twice...

Mac::Safari::JavaScript - 2014-12-02

Christmas is coming. There aren't many shopping days left, and it's time to get organized when it comes to gift buying!

This year I decided I wanted to create an on-disk database of all the present ideas that I had for people. It's nothing more than a single table database schema that looks like this:


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CREATE TABLE gifts (
    name TEXT,
    recipient TEXT,
    url TEXT,
    price_in_cents INTEGER
);

 

Turning this SQL into a working database is a one liner involving the sqlite3 command line utility that sqlite3 that ships with OS X.

  bash$ sqlite3 xmas.db < xmas.sql

This creates a simple file based sqlite3 database which has more that sufficient performance for my usage, doesn't require installing any long running daemons (like say PostgreSQL or MySQL do), and can be talked to easily to Perl from DBI via the DBD::SQLite module.

Building the Perl ORM

Okay, now we need to be able to talk to it from Perl. While talking via DBI is easy, using a object relational mapper like DBIx::Class allows us to skip the SQL writing entirely.

First we need to write a bunch of Perl classes that handle the mapping. Or rather, we can use the dbicdump command line utility that ships with DBIx::Class::Schema::Loader to do it all for us:

  bash$ dbicdump -o dump_directory=lib XmasList dbi:SQLite:xmas.db

The dbicdump command inspects the database and writes out a bunch of files for us:

  bash$ find lib
  lib
  lib/XmasList
  lib/XmasList/Result
  lib/XmasList/Result/Gift.pm
  lib/XmasList.pm

Now we can easily write a script to put things in the database without having to write any SQL:


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#!/usr/bin/perl

use strict;
use warnings;

use lib qw(lib);
use XmasList;

my $schema = XmasList->connect("dbi:SQLite:xmas.db");

$schema->resultset('Gift')->create({
   name => "Donation to the Perl 5 Core Maintenance Fund",
   url => "http://www.perlfoundation.org/perl_5_core_maintenance_fund",
   price_in_cents => 100_00,
   recipient => "Leon",
});

 

Populating Directly From Safari

Of course, writing Perl code to insert stuff into my database is still too much work for the lazy programmer that I am. What I really want is the ability to take what I'm directly looking at in my web browser and put it into the database at the click of a button.

Actually, it so happens I can easily write a chunk of JavaScript to work out these details for me. For example, here's a snippet of JavaScript that creates an object with those details for any listing on Etsy.


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{
  "name" : $("h1").text(),
  "price_in_cents" : parseFloat( $("#listing-price .currency-value").text() ) * 100,
  "recipient" : window.prompt("Who is this for?"),
  "url" : document.location.href
};

 

What I need is a way to get this data from JavaScript into my database, ideally via Perl. There's a module for that:


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#!/usr/bin/perl

use strict;
use warnings;

use lib qw(lib);
use XmasList;

use Mac::Safari::JavaScript qw(safari_js);

# run some JavaScript in Safari, and then put the results in a Perl variable
my $data = safari_js <<'END_OF_JAVASCRIPT';
return {
    "name" : $("h1").text(),
    "price_in_cents" : parseFloat( $("#listing-price .currency-value").text() ) * 100,
    "recipient" : window.prompt("Who is this for?"),
    "url" : document.location.href
  };
END_OF_JAVASCRIPT

# put that data in the Database
my $schema = XmasList->connect("dbi:SQLite:xmas.db");
$schema->resultset('Gift')->create(%{ $data });

 

This uses the fact that you can execute arbitary JavaScript in the current Safari window via AppleScript. Of course, this involves several layers of encoding and decoding (from Perl to AppleScript, then from AppleScript to JavaScript, then from JavaScript back to AppleScript and finally AppleScript back to Perl) and several steps so that errors properly propagate, which is the complexity the module handles for us.

While I can trigger the above script by executing it in the terminal, the really really lazy programmer in me just uses a third party application like KeyboardMaestro to trigger the script from a keyboard shortcut.

Okay, enough work. Let's go shopping!

See Also

Gravatar Image This article contributed by: Mark Fowler <mark@twoshortplanks.com>