much progress

src/music_kraken/objects/collection.py

@@ -96,7 +96,7 @@ class Collection:
                     return AppendResult(True, existing_object, False)
 
                 # if the object does already exist
-                # thus merging and don't add it afterwards
+                # thus merging and don't add it afterward
                 if merge_into_existing:
                     existing_object.merge(element)
                     # in case any relevant data has been added (e.g. it remaps the old object)

src/music_kraken/objects/parents.py

@@ -11,6 +11,10 @@ class DatabaseObject:
     COLLECTION_ATTRIBUTES: tuple = tuple()
     SIMPLE_ATTRIBUTES: dict = dict()
 
+    # contains all collection attributes, which describe something "smaller"
+    # e.g. album has songs, but not artist.
+    DOWNWARDS_COLLECTION_ATTRIBUTES: tuple = tuple()
+
     def __init__(self, _id: int = None, dynamic: bool = False, **kwargs) -> None:
         self.automatic_id: bool = False
 

src/music_kraken/objects/song.py

@@ -204,6 +204,8 @@ class Album(MainObject):
         "notes": FormattedText()
     }
 
+    DOWNWARDS_COLLECTION_ATTRIBUTES = ("song_collection",)
+
     def __init__(
             self,
             _id: int = None,
@@ -422,6 +424,8 @@ class Artist(MainObject):
         "general_genre": ""
     }
 
+    DOWNWARDS_COLLECTION_ATTRIBUTES = ("feature_song_collection", "main_album_collection")
+
     def __init__(
             self,
             _id: int = None,
@@ -646,6 +650,8 @@ class Label(MainObject):
         "notes": FormattedText()
     }
 
+    DOWNWARDS_COLLECTION_ATTRIBUTES = COLLECTION_ATTRIBUTES
+
     def __init__(
             self,
             _id: int = None,