Tuning the node preloading
Every document is stored in the repository by a PHPCR node. Some repositories allow to provide a hint how many levels deep nodes should be loaded. If you know already that you will need the child nodes of a node, you can tell this the DocumentManager to maybe gain some performance. Be careful though, if the document you load has many children, and you only need a few of them, preloading them all might be more expensive then the repeated trips to the content repository to load the actually used children one by one.
This feature can either be used when mapping a Children collection or via
an explicit call to UnitOfWork::setFetchDepth to set a global default fetch depth for this session:
$ dm->getUnitOfWork()->setFetchDepth(2);