Question

How is it done?

I have a Model class that is the parent to many sub-classes, and that Model depends on a database connection and a caching mechanism.

Now, this is where it starts getting troublesome: I have no control over how each object gets instantiated or used, but I have control over methods that get used by the sub-classes.

Currently I have resorted to using static methods and properties for dependency injection, as such:

class Model
{
    private static $database_adapter;
    private static $cache_adapter;
    public static function setDatabaseAdapter(IDatabaseAdapter $databaseAdapter)
    {
        self::$databaseAdapter = $databaseAdapter;
    }
    public static function setCacheAdapter(ICacheAdapter $cacheAdapter)
    {
        self::$cacheAdapter = $cacheAdapter;
    }
}

Which has worked out well, but it feels dirty (it creates a global state for all Models).

I have considered the factory pattern, but that removes the control of the instantiation from the sub-classes (how do I instantiate an object with a variable number of parameters in it’s constructor?).

Now I am at a loss. Any help would be appreciated.

Answer 1

As far as I know this is a perfectly acceptable alternative. Another possibility suggested by Sebastian Bergmann, the creator of PHPUnit, is to have a $testing static property. You can read his recent article regarding the Testing of Singletons. It sounds like you have similar issues.