Create object_cache.py

this is a file/class where I can cache db obj

This is a cache for the objects, that et pulled out of the database.
This is necessary, to not have duplicate objects with the same id.

Using a cache that maps the ojects to their id has multiple benefits:
 - if you modify the object at any point, all objects with the same id get modified *(copy by reference)*
 - less ram usage

src/music_kraken/database/object_cache.py

@@ -0,0 +1,60 @@
+from typing import Dict, List
+
+from .objects import MusicObject
+
+"""
+This is a cache for the objects, that et pulled out of the database.
+This is necessary, to not have duplicate objects with the same id.
+
+Using a cache that maps the ojects to their id has multiple benefits:
+ - if you modify the object at any point, all objects with the same id get modified *(copy by reference)*
+ - less ram usage
+"""
+
+class ObjectCache:
+    """
+    :attr object_to_id: maps any object from the Database like Song or Artist to its id.
+    """
+    object_to_id: Dict[str, MusicObject]
+
+    def __init__(self) -> None:
+        self.object_to_id = dict()
+    
+
+    def clear(self) -> None:
+        """
+        deletes all references and lets the gc clean up the rest
+        this should free up memorie.
+
+        If not, check if you have any references to an object in you're code.
+        It is likely that this object crossreferences to many objects
+        """
+        self.object_to_id = dict()
+
+    def exists(self, music_object: MusicObject) -> bool:
+        """
+        :returns exist: if an element with the same id exists it returns true, else false
+        """
+        if music_object.dynamic:
+            return True
+        if music_object.id in self.object_to_id:
+            return True
+        return False
+
+    def append(self, music_object: MusicObject) -> bool:
+        """
+        :returns exist: if an element with the same id exists it returns true, else false
+        """
+        if self.exists(music_object):
+            return True
+
+        self.object_to_id[music_object.id] = music_object
+
+        return False
+
+    def extent(self, music_object_list: List[MusicObject]):
+        """
+        adjacent to the extend method of list, this appends n Object
+        """
+        for music_object in music_object_list:
+            self.append(music_object)