Lazy loading of object variables in php using __get()

Was doing a(nother) shopping application lately. In the application each Product (a class) can have many images, but they’re not displayed in the search results page or the basket page, so it seemed a bit daft to be reading the database and loading them into memory in the constructor.

What I did instead was to use the magic method __get() to load the images into the object when they were needed. __get() is called whenever something tries to access a variable that is not set or publically accessible, so basically I used that to load the images whenever some other piece of code tried to access Product::images.

Here’s the actual code:

public function __get($var)
{
    eval("$this->_load".$var."();");
    $this->{"_load".$var}();
    return $this->$var;
}

So if some other piece of code made a Product object called $product and then tried to access $product->images and the images haven’t already been loaded, a (private) function called $product->_loadimages() is called. If the images HAVE already been loaded then __get() is not called.

Very handy.

One other thing I had to so was to unset() Product::images in the constructor, so that __get() would be called when something tried to access it. I could have avoided this by making $images private, but it behaves as a public property so I didn’t want to.