111 lines
4.0 KiB
Python
111 lines
4.0 KiB
Python
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from collections import defaultdict
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from typing import Dict, List, Optional
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import weakref
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from .parents import DatabaseObject
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"""
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This is a cache for the objects, that et pulled out of the database.
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This is necessary, to not have duplicate objects with the same id.
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Using a cache that maps the ojects to their id has multiple benefits:
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- if you modify the object at any point, all objects with the same id get modified *(copy by reference)*
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- less ram usage
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- to further decrease ram usage I only store weak refs and not a strong reference, for the gc to still work
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"""
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class ObjectCache:
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"""
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ObjectCache is a cache for the objects retrieved from a database.
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It maps each object to its id and uses weak references to manage its memory usage.
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Using a cache for these objects provides several benefits:
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- Modifying an object updates all objects with the same id (due to copy by reference)
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- Reduced memory usage
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:attr object_to_id: Dictionary that maps DatabaseObjects to their id.
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:attr weakref_map: Dictionary that uses weak references to DatabaseObjects as keys and their id as values.
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:method exists: Check if a DatabaseObject already exists in the cache.
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:method append: Add a DatabaseObject to the cache if it does not already exist.
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:method extent: Add a list of DatabaseObjects to the cache.
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:method remove: Remove a DatabaseObject from the cache by its id.
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:method get: Retrieve a DatabaseObject from the cache by its id. """
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object_to_id: Dict[str, DatabaseObject]
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weakref_map: Dict[weakref.ref, str]
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def __init__(self) -> None:
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self.object_to_id = dict()
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self.weakref_map = defaultdict()
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def exists(self, database_object: DatabaseObject) -> bool:
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"""
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Check if a DatabaseObject with the same id already exists in the cache.
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:param database_object: The DatabaseObject to check for.
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:return: True if the DatabaseObject exists, False otherwise.
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"""
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if database_object.dynamic:
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return True
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return database_object.id in self.object_to_id
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def on_death(self, weakref_: weakref.ref) -> None:
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"""
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Callback function that gets triggered when the reference count of a DatabaseObject drops to 0.
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This function removes the DatabaseObject from the cache.
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:param weakref_: The weak reference of the DatabaseObject that has been garbage collected.
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"""
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data_id = self.weakref_map.pop(weakref_)
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self.object_to_id.pop(data_id)
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def get_weakref(self, database_object: DatabaseObject) -> weakref.ref:
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return weakref.ref(database_object, self.on_death)
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def append(self, database_object: DatabaseObject) -> bool:
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"""
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Add a DatabaseObject to the cache.
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:param database_object: The DatabaseObject to add to the cache.
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:return: True if the DatabaseObject already exists in the cache, False otherwise.
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"""
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if self.exists(database_object):
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return True
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self.weakref_map[weakref.ref(database_object, self.on_death)] = database_object.id
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self.object_to_id[database_object.id] = database_object
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return False
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def extent(self, database_object_list: List[DatabaseObject]):
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"""
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adjacent to the extent method of list, this appends n Object
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"""
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for database_object in database_object_list:
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self.append(database_object)
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def remove(self, _id: str):
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"""
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Remove a DatabaseObject from the cache.
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:param _id: The id of the DatabaseObject to remove from the cache.
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"""
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data = self.object_to_id.get(_id)
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if data:
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self.weakref_map.pop(weakref.ref(data))
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self.object_to_id.pop(_id)
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def __getitem__(self, item) -> Optional[DatabaseObject]:
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"""
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this returns the data obj
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:param item: the id of the music object
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:return:
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"""
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return self.object_to_id.get(item)
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def get(self, _id: str) -> Optional[DatabaseObject]:
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return self.__getitem__(_id)
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