Initialize a FileRField with automatic file-based persistence.

The field is configured to store file path references in KV_STORE and is excluded from dict views since the actual data is in files.

Deserialize field value by loading data from the file path.

This method is marked as final and cannot be overridden. It delegates to the load_from_file method which must be implemented by subclasses.

Serialize and save the field value to a file.

This abstract method must be implemented by subclasses to define how data is serialized and written to the file. It is called automatically when the Resource is saved.

The data MUST be written to the exact file path provided. The directory containing the file is guaranteed to exist.

Get the default value for this field.

If the default value is a Type or Callable, it will be called to generate a new default value. Otherwise, the default value is returned directly.

This ensures that mutable defaults (like lists or dicts) are not shared between Resource instances.

Load and deserialize the field value from a file.

This abstract method must be implemented by subclasses to define how data is read and deserialized from the file. It is called automatically when the Resource is loaded.

The file at file_path is guaranteed to exist when this method is called.

Serialize method not used for FileRField.

The actual serialization is handled by dump_to_file which is called by the resource persistence layer. This method exists for interface compatibility but should be ignored.