diff --git a/matemat/db/database.py b/matemat/db/database.py
index 1b49c76..5c41300 100644
--- a/matemat/db/database.py
+++ b/matemat/db/database.py
@@ -254,7 +254,7 @@ class Database(object):
                 FROM products
               '''):
                 product_id, name, price_member, price_external = row
-                products.append(Product(product_id, name, price_member, price_external))
+                products.append(Product.from_database(product_id, name, price_member, price_external))
         return products
 
     def create_product(self, name: str, price_member: int, price_non_member: int) -> Product:
@@ -273,9 +273,11 @@ class Database(object):
             })
             c.execute('SELECT last_insert_rowid()')
             product_id = int(c.fetchone()[0])
-        return Product(product_id, name, price_member, price_non_member)
+        return Product.from_database(product_id, name, price_member, price_non_member)
 
     def change_product(self, product: Product):
+        if product.id == -1:
+            raise ValueError('Invalid product ID')
         with self.transaction() as c:
             c.execute('''
             UPDATE products
@@ -291,6 +293,8 @@ class Database(object):
             })
 
     def delete_product(self, product: Product):
+        if product.id == -1:
+            raise ValueError('Invalid product ID')
         with self.transaction() as c:
             c.execute('''
             DELETE FROM products
@@ -298,6 +302,8 @@ class Database(object):
             ''', [product.id])
 
     def increment_consumption(self, user: User, product: Product, count: int = 1):
+        if product.id == -1:
+            raise ValueError('Invalid product ID')
         with self.transaction() as c:
             c.execute('''
             SELECT count
@@ -342,6 +348,8 @@ class Database(object):
             })
 
     def restock(self, product: Product, count: int):
+        if product.id == -1:
+            raise ValueError('Invalid product ID')
         with self.transaction() as c:
             c.execute('''
             UPDATE products
diff --git a/matemat/primitives/Product.py b/matemat/primitives/Product.py
index 9a97050..a761064 100644
--- a/matemat/primitives/Product.py
+++ b/matemat/primitives/Product.py
@@ -1,28 +1,24 @@
 
-from inspect import stack
-
-
 class Product(object):
 
-    def __init__(self):
-        print(stack())
-        self._product_id: int = 0
-        self._name: str = ''
-        self._price_member: int = 0
-        self._price_non_member: int = 0
-        raise NotImplementedError('This shoudt not be called!')
+    def __init__(self,
+                 product_id: int = -1,
+                 name: str = '',
+                 price_member: int = 0,
+                 price_non_member: int = 0):
+        self._product_id: int = product_id
+        self._name: str = name
+        self._price_member: int = price_member
+        self._price_non_member: int = price_non_member
 
-    # def __init__(self,
-    #              product_id: int,
-    #              name: str,
-    #              price_member: int,
-    #              price_non_member: int):
-    #     if product_id == -1:
-    #         raise ValueError('Invalid product ID')
-    #     self._product_id: int = product_id
-    #     self._name: str = name
-    #     self._price_member: int = price_member
-    #     self._price_non_member: int = price_non_member
+    @classmethod
+    def from_database(cls,
+                      product_id: int,
+                      name: str,
+                      price_member: int,
+                      price_non_member: int) -> 'Product':
+        product = cls(product_id, name, price_member, price_non_member)
+        return product
 
     @property
     def id(self) -> int: