diff --git a/music_kraken/objects/collection.py b/music_kraken/objects/collection.py
index e4905dc..1fba27d 100644
--- a/music_kraken/objects/collection.py
+++ b/music_kraken/objects/collection.py
@@ -37,39 +37,33 @@ class Collection(Generic[T]):
         self.contain_given_in_attribute: Dict[str, Collection] = contain_given_in_attribute or {}
         self.append_object_to_attribute: Dict[str, T] = append_object_to_attribute or {}
 
-        self._indexed_values = defaultdict(set)
-        self._indexed_to_objects = defaultdict(list)
+        self._id_to_index_values: Dict[int, set] = defaultdict(set)
+        self._indexed_values = defaultdict(lambda: None)
+        self._indexed_to_objects = defaultdict(lambda: None)
 
         self.extend(data)
 
     def _map_element(self, __object: T, from_map: bool = False):
-        __object._inner._mapped_in_collection.add(self)
         self._contains_ids.add(__object.id)
 
         for name, value in __object.indexing_values:
             if value is None or value == __object._inner._default_values.get(name):
                 continue
 
-            self._indexed_values[name].add(value)
-            self._indexed_to_objects[value].append(__object)
+            self._indexed_values[name] = value
+            self._indexed_to_objects[value] = __object
+
+            self._id_to_index_values[__object.id].add((name, value))
 
     def _unmap_element(self, __object: T):
         if __object.id in self._contains_ids:
             self._contains_ids.remove(__object.id)
 
-        for name, value in __object.indexing_values:
-            if value is None:
-                continue
-            if value not in self._indexed_values[name]:
-                continue
+        for name, value in self._id_to_index_values[__object.id]:
+            del self._indexed_values[name]
+            del self._indexed_to_objects[value]
 
-            try:
-                self._indexed_to_objects[value].remove(__object)
-            except ValueError:
-                continue
-
-            if not len(self._indexed_to_objects[value]):
-                self._indexed_values[name].remove(value)
+        del self._id_to_index_values[__object.id]
 
     def _contained_in_self(self, __object: T) -> bool:
         if __object.id in self._contains_ids:
@@ -78,7 +72,7 @@ class Collection(Generic[T]):
         for name, value in __object.indexing_values:
             if value is None:
                 continue
-            if value in self._indexed_values[name]:
+            if value == self._indexed_values[name]:
                 return True
         return False
 
@@ -150,8 +144,8 @@ class Collection(Generic[T]):
             if value is None:
                 continue
 
-            if value in self._indexed_values[name]:
-                existing_object = self._indexed_to_objects[value][0]
+            if value == self._indexed_values[name]:
+                existing_object = self._indexed_to_objects[value]
                 if existing_object.id == __object.id:
                     return None
 
@@ -173,8 +167,8 @@ class Collection(Generic[T]):
 
     def _find_object_in_self(self, __object: T) -> Optional[T]:
         for name, value in __object.indexing_values:
-            if value in self._indexed_values[name]:
-                return self._indexed_to_objects[value][0]
+            if value == self._indexed_values[name]:
+                return self._indexed_to_objects[value]
 
     def _find_object(self, __object: T, no_sibling: bool = False) -> Tuple[Collection[T], Optional[T]]:
         other_object = self._find_object_in_self(__object)
@@ -237,6 +231,8 @@ class Collection(Generic[T]):
                 return
 
             append_to._unmap_element(existing_object)
+            append_to._unmap_element(__object)
+
             existing_object.merge(__object)
             append_to._map_element(existing_object)