A database file can be partitioned only if:
At most, one class is mapped to the file.
Mapping more than one class to a partitioned file would defeat many of the benefits of partitioning, so this is explicitly disallowed. You can enable partitioning on a file before a singleton class is mapped to it, so zero classes mapped to the file is valid.
No Collection classes are mapped to the file.
Directly mapping collection classes to a partitioned file is not supported, but collection partitioning can be achieved by partitioning the parent class.