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Persistence

The Persistable class is a mixin for objects that need to be persisted. It provides a persistent method that can be used to make the object persistent.

Derived classes must implement the backup_to_dict and restore_from_dict methods.

Note that the persistence module contains a number of helper functions:

  • to_dict: converts (dictionaries or lists of) dataclasses into a dictionary (or list)
  • from_dict: converts a dictionary into a dataclass of given type
  • replace_dict: replaces the content of a dictionary using from_dict for each item
  • replace_list: replaces the content of a list using from_dict for each item
  • replace_set: replaces the content of a set using from_dict for each item
  • replace_dataclass: replaces the attributes of a dataclass with the values of a dictionary

Further helper functions can be used for importing and exporting all persistable objects:

  • The export_all method can be used to export all persistable objects to a dictionary.
  • The import_all method can be used to import all persistable objects from a dictionary.
  • Likewise, export_button and import_button are UI elements based on these two methods that can be added to a page.

By default, data is stored in the ~/.rosys directory. The filename is derived from the module name. Both can be changed by setting the path and key parameters of the persistent method.

If you want to automatically keep daily backups, you can use the BackupSchedule module. It will backup all the contents of your ~/.rosys directory at a configurable directory and at a given time each day. When a maximum number of backup files is reached (specified with backup_count), it will delete the oldest file.

You should choose wisely which values to persist. In particular, avoid to persist volatile things like wheel odometry or other sensor readings to save CPU and IO bandwidth.

Migration from the old PersistentModule class

The PersistentModule class has been replaced by the Persistable mixin in version 0.24.0. To migrate, follow these steps:

  1. Replace PersistentModule with Persistable in the class definition.
  2. Rename the backup and restore methods to backup_to_dict and restore_from_dict.
  3. Use the persistent method to make objects persistent which used to be derived from PersistentModule: KpiLogger, Schedule, PathPlanner, CameraProvider and derived classes.
  4. If you called PersistentModule with a persistence_key, remove it and use the key parameter of the persistent method instead.