getPersistenceKey property
By default, a document is persisted to a file by its collection name. If documents in the same collection should be broken into multiple files (due to large collection sizes, etc) or documents should be grouped together across different collections (due to small collection sizes, etc) then the persistenc key can be used to group arbitrary documents together into the same persistence file.
Implementation
final String? Function(Document doc)? getPersistenceKey;