diff --git a/db/SQLiteClient.py b/db/SQLiteClient.py
index 9c7d21b..390c94d 100644
--- a/db/SQLiteClient.py
+++ b/db/SQLiteClient.py
@@ -45,7 +45,8 @@ def get_user_by_email(email: str):
 def update_user(id: int, name: str, email: str, password: str = None):
     now = datetime.now().isoformat()
     if password:
-        query = f"UPDATE users SET name = '{name}', email = '{email}', password = '{password}', updated_at = '{now}' WHERE id = {id};"
+        query = (f"UPDATE users SET name = '{name}', email = '{email}', password = '{password}', updated_at = '{now}' "
+                 f"WHERE id = {id};")
     else:
         query = f"UPDATE users SET name = '{name}', email = '{email}', updated_at = '{now}' WHERE id = {id};"
     conn = con3()
@@ -57,12 +58,10 @@ def update_user(id: int, name: str, email: str, password: str = None):
 
 
 def delete_user(id: int):
-    query = f"DELETE FROM habit_lists WHERE (SELECT list_id FROM habit_users WHERE user_id = {id}) = id;"
-    query2 = f"DELETE FROM users WHERE id = {id};"
+    query = f"DELETE FROM users WHERE id = {id};"
     conn = con3()
     cursor = conn.cursor()
     cursor.execute(query)
-    cursor.execute(query2)
     conn.commit()
     conn.close()
     return cursor.lastrowid
@@ -71,8 +70,8 @@ def delete_user(id: int):
 ### Habit.py ###
 def create_habit(list_id: int, name: str, times: int, unit: int, slot: int, note: str | None=None):
     now = datetime.now().isoformat()
-    query = (f"INSERT INTO habits (list_id, name, note, times, unit, slot, created_at, updated_at) VALUES ('{list_id}', "
-             f"'{name}', '{note}', '{times}', '{unit}', '{slot}', '{now}', '{now}');")
+    query = (f"INSERT INTO habits (list_id, name, note, times, unit, slot, created_at, updated_at) "
+             f"VALUES ('{list_id}', '{name}', '{note}', '{times}', '{unit}', '{slot}', '{now}', '{now}');")
     conn = con3()
     cursor = conn.cursor()
     cursor.execute(query)
@@ -168,7 +167,8 @@ def update_slot(id: int, slot: int):
 
 def update_habit(id: int, name: str, note: str, times: int, unit: int):
     now = datetime.now().isoformat()
-    query = f"UPDATE habits SET name = {name}, note = {note}, times = {times}, unit = {unit}, updated_at = '{now}' WHERE id = {id};"
+    query = (f"UPDATE habits SET name = {name}, note = {note}, times = {times}, unit = {unit}, updated_at = '{now}' "
+             f"WHERE id = {id};")
     conn = con3()
     cursor = conn.cursor()
     cursor.execute(query)
@@ -178,10 +178,12 @@ def update_habit(id: int, name: str, note: str, times: int, unit: int):
 
 
 def delete_habit(id: int):
-    query = f"DELETE FROM habits WHERE id = {id};"
+    query = f"DELETE FROM habit_trackings WHERE id = habit_id;"
+    query2 = f"DELETE FROM habits WHERE id = {id};"
     conn = con3()
     cursor = conn.cursor()
     cursor.execute(query)
+    cursor.execute(query2)
     conn.commit()
     conn.close()
 
@@ -264,6 +266,37 @@ def get_habitLists(user_id: int):
     return habit_lists
 
 
+def get_users(list_id: int):
+    query = (f"SELECT users.* FROM users JOIN habit_users ON users.id = habit_users.user_id WHERE "
+             f"habit_users.list_id = {list_id};")
+    conn = con3()
+    cursor = conn.cursor()
+    cursor.execute(query)
+    users = cursor.fetchall()
+    conn.close()
+    return users
+
+
+def add_user(list_id: int, user_id: int):
+    now = datetime.now().isoformat()
+    query = (f"INSERT INTO habit_users (user_id, list_id, created_at, updated_at)"
+              f" VALUES ('{user_id}', '{list_id}', '{now}', '{now}');")
+    conn = con3()
+    cursor = conn.cursor()
+    cursor.execute(query)
+    conn.commit()
+    conn.close()
+
+
+def remove_user(list_id: int, user_id: int):
+    query = f"DELETE FROM habit_lists WHERE user_id = {user_id} AND list_id = {list_id};"
+    conn = con3()
+    cursor = conn.cursor()
+    cursor.execute(query)
+    conn.commit()
+    conn.close()
+
+
 def update_habitList(id: int, name: str, description: str):
     now = datetime.now().isoformat()
     query = f"UPDATE habit_lists SET name = {name}, description = {description}, updated_at = '{now}' WHERE id = {id};"
@@ -284,16 +317,6 @@ def delete_habitList(id: int):
     conn.close()
 
 
-def get_users(list_id: int):
-    query = f"SELECT users.* FROM users JOIN habit_users ON users.id = habit_users.user_id WHERE habit_users.list_id = {list_id};"
-    conn = con3()
-    cursor = conn.cursor()
-    cursor.execute(query)
-    users = cursor.fetchall()
-    conn.close()
-    return users
-
-
 if __name__ == "__main__":
     habits = get_habits(1)
     for habit in habits:
diff --git a/models/Habit.py b/models/Habit.py
index 9c26954..35faf65 100644
--- a/models/Habit.py
+++ b/models/Habit.py
@@ -3,11 +3,11 @@ from dataclasses import dataclass
 from datetime import datetime
 
 from models.HabitTrackings import HabitTrackings
-from db.SQLiteClient import update_slot, create_habit, get_habit, delete_habit, get_next_slot, \
-    get_habitTrackings_by_habit_id, get_slots, update_habit, get_habitList
+from db.SQLiteClient import (create_habit, get_habit, update_habit, delete_habit, get_next_slot, get_slots, update_slot,
+                             get_habitTrackings_by_habit_id, get_habitList)
 
 
-# Unit wird als Integers wie folgt gemessen:
+# Unit wird als Integer wie folgt gemessen:
 # 0: Tag
 # 1: Woche (Default)
 # 2: Monat
@@ -36,9 +36,7 @@ class Habit:
     @staticmethod
     def get(id: int):
         habit = get_habit(id)
-        habit = Habit(habit[0], habit[1], habit[2], habit[3], habit[4], habit[5], habit[6]) if habit else None
-
-        return habit
+        return Habit(habit[0], habit[1], habit[2], habit[3], habit[4], habit[5], habit[6]) if habit else None
 
     def update(self, name: str=None, note: str=None, times: int=None, unit: int=None):
         update_habit(self.id, name, note, times, unit)
@@ -69,13 +67,17 @@ class Habit:
             update_slot(slot[0], slot[1] - 1)
         delete_habit(self.id)
 
-    def get_habitTrackings(self) -> list[HabitTrackings]:
+    def get_habitTrackings(self) -> list:
         trackings = []
         for rawTracking in get_habitTrackings_by_habit_id(self.id):
-            trackings.append(HabitTrackings(rawTracking[0], rawTracking[1],
-                                            datetime.strptime(rawTracking[2], "%Y-%m-%dT%H:%M:%S.%f")))
+            trackings.append(HabitTrackings(rawTracking[0], rawTracking[1]))
         return trackings
 
+    def habit_list(self):
+        from models.HabitList import HabitList
+        raw_habitLists = get_habitList(self.list_id)
+        return HabitList(raw_habitLists[0], raw_habitLists[1], raw_habitLists[2]) if raw_habitLists else None
+
     def fill_statistics(self):
         count = 0
         self.checked = False
@@ -104,11 +106,3 @@ class Habit:
 
     def to_json(self):
         return json.dumps(self, default=lambda o: o.__dict__, sort_keys=True, indent=4)
-
-    def habit_list(self):
-        from models.HabitList import HabitList
-        raw_habitLists = get_habitList(self.list_id)
-        return HabitList(raw_habitLists[0], raw_habitLists[1], raw_habitLists[2],
-                         datetime.strptime(raw_habitLists[3], "%Y-%m-%dT%H:%M:%S.%f"),
-                         datetime.strptime(raw_habitLists[4], "%Y-%m-%dT%H:%M:%S.%f")) \
-        if raw_habitLists else None
diff --git a/models/HabitList.py b/models/HabitList.py
index d59e265..64fa292 100644
--- a/models/HabitList.py
+++ b/models/HabitList.py
@@ -1,9 +1,10 @@
 from dataclasses import dataclass
-from datetime import date, datetime
+from datetime import datetime
 
-from db.SQLiteClient import delete_habitList, create_habitList, get_habitList, get_habits, get_users
 from models.Habit import Habit
 from models.User import User
+from db.SQLiteClient import (delete_habitList, create_habitList, get_habitList, get_habits,
+                             get_users, add_user, remove_user)
 
 
 @dataclass
@@ -11,24 +12,19 @@ class HabitList:
     id: int
     name: str
     description: str
-    created_at: date
-    updated_at: date
     habits: list = None
 
     @staticmethod
     def create(user_id: int, name: str, description: str):
         id = create_habitList(user_id, name, description)
-        return HabitList(id, name, description, datetime.now(), datetime.now())
+        return HabitList(id, name, description)
 
     @staticmethod
     def get(id: int):
         habitList = get_habitList(id)
         return HabitList(habitList[0], habitList[1], habitList[2], datetime.strptime(habitList[3], "%Y-%m-%dT%H:%M:%S.%f"), datetime.strptime(habitList[4], "%Y-%m-%dT%H:%M:%S.%f")) if habitList else None
 
-    def delete(self):
-        delete_habitList(self.id)
-
-    def get_habits(self):
+    def get_habits(self) -> list:
         raw_habits = get_habits(self.id)
         habits = []
         for habit in raw_habits:
@@ -37,7 +33,7 @@ class HabitList:
 
         return habits
 
-    def get_users(self):
+    def get_users(self) -> list:
         raw_users = get_users(self.id)
         users = []
         for user in raw_users:
@@ -45,3 +41,14 @@ class HabitList:
             users.append(user)
 
         return users
+
+    def add_user(self, email: str):
+        user = User.get_by_email(email)
+        add_user(self.id, user.id)
+
+    # The id of the current user is necessary
+    def delete(self, user_id):
+        if len(get_users) > 1:
+            remove_user(self.id, user_id)
+        else:
+            delete_habitList(self.id)
diff --git a/models/HabitTrackings.py b/models/HabitTrackings.py
index 9ad30f1..996aed6 100644
--- a/models/HabitTrackings.py
+++ b/models/HabitTrackings.py
@@ -1,6 +1,4 @@
 from dataclasses import dataclass
-from datetime import date, datetime
-
 from db.SQLiteClient import create_habitTrackings, get_habitTrackings, delete_habitTrackings
 
 
@@ -8,17 +6,16 @@ from db.SQLiteClient import create_habitTrackings, get_habitTrackings, delete_ha
 class HabitTrackings:
     id: int
     habit_id: int
-    created_at: date
 
     @staticmethod
-    def create(habit_id: int, times: int):
+    def create(habit_id: int):
         id = create_habitTrackings(habit_id)
-        return HabitTrackings(id, habit_id, datetime.now())
+        return HabitTrackings(id, habit_id)
 
     @staticmethod
     def get(id: int):
         habitTrackings = get_habitTrackings(id)
-        return HabitTrackings(habitTrackings[0], habitTrackings[1], datetime.strptime(habitTrackings[2], "%Y-%m-%dT%H:%M:%S.%f")) if habitTrackings else None
+        return HabitTrackings(habitTrackings[0], habitTrackings[1]) if habitTrackings else None
 
     def delete(self):
         delete_habitTrackings(self.id)
diff --git a/models/User.py b/models/User.py
index 13f9f72..e058fc3 100644
--- a/models/User.py
+++ b/models/User.py
@@ -1,8 +1,8 @@
 from datetime import datetime
 
 from flask_login import UserMixin
-from db.SQLiteClient import create_user, get_user, get_user_by_email, delete_user, update_user, \
-    get_habitLists, get_heatmap_value
+from db.SQLiteClient import (create_user, get_user, get_user_by_email, update_user, delete_user,
+                             get_habitLists, get_heatmap_value)
 
 
 class User(UserMixin):
@@ -31,9 +31,12 @@ class User(UserMixin):
         update_user(self.id, self.name, self.email, self.password if self.password else None)
 
     def delete(self):
+        habitLists = self.get_habitLists()
+        for habitList in habitLists:
+            habitList.delete(self.id)
         delete_user(self.id)
 
-    def get_habitLists(self):
+    def get_habitLists(self) -> list:
         from models.HabitList import HabitList
 
         raw_habitLists = get_habitLists(self.id)
@@ -44,7 +47,7 @@ class User(UserMixin):
 
         return habitLists
 
-    def get_heatmap(self):
+    def get_heatmap(self) -> list:
         heatmap = []
         for day in range (0, 27):
             value = get_heatmap_value(self.id, day)