diff --git a/src/budy/models/bag.py b/src/budy/models/bag.py
index ab5b5ae7..8d6e3b9c 100644
--- a/src/budy/models/bag.py
+++ b/src/budy/models/bag.py
@@ -146,6 +146,18 @@ def add_product_s(self, product, quantity = 1.0):
         )
         self.add_line_s(_bag_line)
 
+    def add_update_line_s(self, bag_line):
+        self.add_product_s(
+            bag_line.product,
+            quantity = bag_line.quantity
+        )
+
+    def merge_s(self, bag_id):
+        bag = Bag.get(id = bag_id)
+        for line in bag.lines:
+            line = line.clone()
+            self.add_update_line_s(line)
+
     def _calculate(self):
         lines = self.lines if hasattr(self, "lines") else []
         self.total = sum(line.total for line in lines)
diff --git a/src/budy/test/bag.py b/src/budy/test/bag.py
index ba678464..6f0c7f8d 100644
--- a/src/budy/test/bag.py
+++ b/src/budy/test/bag.py
@@ -114,3 +114,43 @@ def test_basic(self):
 
         self.assertEqual(bag.total, 0.0)
         self.assertEqual(len(bag.lines), 0)
+
+    def test_merge(self):
+        product = budy.Product.new(
+            short_description = "product",
+            gender = "Male",
+            price = 10.0,
+            form = False
+        )
+        product.save()
+
+        bag = budy.Bag.new(form = False)
+        bag.save()
+
+        bag_line = budy.BagLine.new(
+            quantity = 2.0,
+            form = False
+        )
+        bag_line.product = product
+        bag_line.save()
+        bag.add_line_s(bag_line)
+
+        self.assertEqual(bag_line.quantity, 2.0)
+        self.assertEqual(bag_line.total, 20.0)
+        self.assertEqual(bag.total, 20.0)
+        self.assertEqual(len(bag.lines), 1)
+
+        extra = budy.Bag.new(form = False)
+        extra.save()
+
+        self.assertEqual(len(extra.lines), 0)
+
+        extra.merge_s(bag.id)
+
+        self.assertEqual(extra.total, 20.0)
+        self.assertEqual(len(extra.lines), 1)
+
+        extra.merge_s(bag.id)
+
+        self.assertEqual(extra.total, 40.0)
+        self.assertEqual(len(extra.lines), 1)