Tag: PHP

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Hackday

Well, Hackday was certainly an experience – the lightning strike and the roof vents opening was really quite disturbing! The lack of WiFi early on was a real pain as it made it very hard to connect projects, people and skills, so I suspect that most hacks were done by people who had arranged something beforehand, or who happened to meet at the bus stop.

Anyway, I got involved, along with Rob, Andy, Edward and James in something that turned into Fruitr – the search engine for unimaginative chefs. The basic idea was: take a picture of a piece of fruit, submit it to our site, and you’re rewarded with recipes that use that fruit. Rob and James worked on using a C++ image recognition library (not sure which one) from a Pylons Python app, which was driven by statistical matching against images from Flickr that are tagged with ‘fruitr’. Edward provided API access to his database of recipes courtesy of his site BigMunch, and I developed the testing web interface (later rolled into the main python app), and the email (in and out) interface. Andy had an abortive attempt at creating a J2ME app to talk to it, but was hampered by BlueTooth interference, buggy phones and poor mobile reception. We really had it all running by about midnight, and just a final polish was needed in the morning.

I spent much of Sunday looking at APIs to use with AMEE, without much luck or inspiration, then messed about creating an Apple Quartz Composer file that can be used as a screen saver. It grabs images tagged with ‘hackdaylondon’ from Flickr and presents them on faces of a bunch of rotating cubes. One face of the cubes displays live video (assuming you’re on a Mac Book? or similar which has a camera). There is also a spectrum-driven audio bar display, and a rotating Hack Day logo, which is also moved by sound. You can download the Quartz composer file.

I did the presentations for both hacks. For the Fruitr one I just ran out of time – sweaty fingers and trackpads really don’t mix. Because demoing a screen saver is not too hard, I dressed it up as a load of presentation faux-pas. I hope nobody thought it was for real!

Generally it was all pretty good fun, and it certainly had an excellent atmosphere, not to mention the endless supply of chocolate. Playing doubles tennis on the Wii at 2am was another highlight, along with the “non-showing” of Doctor Who…

I needed to leave before prizes and the Rumble Strips gig, so I missed out on that bit, and at the end of it all, I completely failed to grab a pink bean bag for Z. Oh well, I’ll be back next year!

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CakePHP’s invisible query cache

I just wanted to document something that was driving me nuts in Cake PHP.

I do a simple find on a model:

$thing = $this->Model->find(array('id' => 123), NULL, NULL, 1);

Then later on, I make the same query again. Only the first query appears in the SQL debug output. Why call it again? Well, I’ve made some manual queries in between the calls using SQL that is inconvenient to emulate in Cake functions, in particular INSERT IGNORE. It turns out that Cake has a largely undocumented query cache, but Cake has no idea that its cache is dirty because of the manual queries. The _clearCache function is not yet implemented for the query cache, so the only choice is to disable it before the first query, and you can do that during a single instantiation by saying:

$this->Model->cacheQueries = false;

Note that the query has 1 level of recursion, which means that all the sub-queries are also cached. Setting cacheQueries to false on this one model means that all queries through it don’t get cached, including those that may be in other models via relationships.

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CakePHP hasManyAndBelongsTo relationship limitations

Cake has some nice support for modeling many to many relations using ‘hasManyAndBelongsTo’. There’s a simple example here.
Though this works well for simple connections between classes, you can’t do much else. Taking the classic Blog-style Posts and Tags example, this approach will easily let you link multiple tags to multiple posts. But what if you want to track the date that a tag was applied to a post? If you add a date field to the join table, it seems pretty much impossible to retrieve it, and setting it is even harder. You can search on it by twiddling with the conditions on the relation, but that’s ugly. I think in that case, you have no option but to model the relation explicitly with two pairs of hasMany/belongsTo relations linked through a PostTag model, and then you’ll have to set your recursion deeper and get busy with unbindmodel in order to keep the number of queries down. Who knows, I might even write up an example and post it here…