The new Doctrine\ODM\MongoDB\Aggregation\Builder::getAggregation() method
returns an Doctrine\ODM\MongoDB\Aggregation\Aggregation instance, comparable
to the Query class.
The Doctrine\ODM\MongoDB\Aggregation\Builder::execute() method was removed.
The Doctrine\ODM\MongoDB\Id\AbstractIdGenerator class has been removed. Custom
ID generators must implement the Doctrine\ODM\MongoDB\Id\IdGenerator
interface.
The Doctrine\ODM\MongoDB\Mapping\ClassMetadata class has been marked final and
will no longer be extendable.
The boolean, integer, and int_id mapping types have been removed. Use the
bool, int, and int types, respectively. These types behave exactly the
same.
The Doctrine\ODM\MongoDB\Proxy\Resolver\ClassNameResolver interface has been
dropped in favor of the Doctrine\Persistence\Mapping\ProxyClassNameResolver
interface.
The getClassNameResolver method in DocumentManager has been removed. To
retrieve the mapped class name for any object or class string, fetch metadata
for the class and read the class using $metadata->getName(). The metadata
layer is aware of these proxy namespace changes and how to resolve them, so
users should always go through the metadata layer to retrieve mapped class
names.