Aggressive model loading is the default model loading method and is very simple, it will look for all files with a .php extension and will include it. Doctrine can not satisfy any inheritance and if your models extend another model, it cannot include them in the correct order so it is up to you to make sure all dependencies are satisfied in each class.
With aggressive model loading you can have multiple classes per file and the file name is not required to be related to the name of the class inside of the file.
The downside of aggressive model loading is that every php file is included in every request, so if you have lots of models it is recommended you use conservative model loading.
To use aggressive model loading we need to set the model loading attribute to be aggressive:
$manager->setAttribute(Doctrine_Core::ATTR_MODEL_LOADING, Doctrine_Core::MODEL_LOADING_AGGRESSIVE);
Aggressive is the default of the model loading attribute so explicitly setting it is not necessary if you wish to use it.
When we use the Doctrine_Core::loadModels() functionality all the classes found will be included right away:
Doctrine_Core::loadModels('/path/to/models');