Upcasting Failure: PHP and String Insanity

One of the most awesome bugs to bite me in PHP is how it handles comparisons. For any two strings, everything's fine. For any two ints, the comparison is what you expect. But, what happens when you compare a string to an int?

<?php
if ('astring' == 0) {
        echo 'insane';
}

This happly little script will print the fact that PHP is, in a word, insane. Clearly, 0 and 'astring' are not the same thing; not even close. 'astring' isn't even falsy.

What's happening here is that PHP is casting both to an integer, instead of to a string. And the rules in PHP say that, since string 'astring' has no leading numerals, it's converted to the number 0. Clearly not what anyone coming from a strongly typed language would expect. The "correct" way is, easily enough, to use === instead of ==.

I thought the insanity stopped there, but then I ran into another gem. We have a select box in one app that allows the user to choose hours, days, weeks, and months:

<select>
    <option value="1/24">Hourly</option>
    <option value="1">Daily</option>
    <option value="7">Weekly</option>
    <option value="31">Monthly</option>
</select>

In the app, we handled this with a switch. It worked beautifully until the time came to add in support for the 'Hourly' option. Javascript kept anyone from actually selecting 'Hourly' until we were done with the backend to support it, but the client wanted to see where the option would be in the final interface.

<?php

switch ($time) {
    case 31:
        // monthly processing
        break;

    case 7:
        // weekly processing
        break;

    case 1: default:
        // daily processing
        break;

    case '1/24':
        // @TODO: add support for this
        break;
}

PHP compares the case labels using == logic. This means everything was coming up daily instead of hourly. Instead, it's better to just leave everything in the switch as a string. Since $input comes in through the $_POST vars, it's a string regardless, and will compare correctly.

But really, why does 0 == 'astring' in the first place, PHP?

:wq

Copy-on-write Semantics on DABL

I've been thinking of a way to do this for a while, and finally got some time to hack out a prototype yesterday.

First, the problem statement. We have a piece of data (street address) that needs to be associated with multiple entities. Basically, I want a many:many relationship between them, but with a catch. Once the address is attached to an entity, it should be manageable on a per-entity basis.

The obvious solution is to make a copy of the data and just attach the copy to the second entity. That's fine, but it's not unrealistic to have 1,000 entities with the same information. That means 1,000 copies of the data, just in case it might change.

So, I implemented a copy-on-write save() method for DABL, our pet ORM/MVC.

(editor's note: DABL is now hosted on github)

The basic idea is that we need to generate a new ID for the record, then pass that new record off to a subset of the related records. If all the related records are to be modified, there's nothing to be gained (except revision history; if you want that, it's trivial) from creating a new record. Rather than letting the database update all the related records, we have to do it ourselves since we only want to CASCADE some of them.

For the source of my prototype pet project, see DABL cow-save() or fork my nonblocking-random repository on github. The basic database setup is a Userdata table which has many Users. Userdata holds the equivalent of GECOS information (firstname, lastname), while User holds the login information (username, password). The production version of this has much more data in the related table and is written in Propel, which makes it significantly uglier.

:wq