diff --git a/modules/purchase_trade/purchase.py b/modules/purchase_trade/purchase.py
index 9bff4d1..85368a2 100755
--- a/modules/purchase_trade/purchase.py
+++ b/modules/purchase_trade/purchase.py
@@ -298,21 +298,21 @@ class Purchase(metaclass=PoolMeta):
         WB = Pool().get('purchase.weight.basis')
         wb = WB.search(['id','>',0])
         if wb:
-            return wb[0]
+            return wb[0].id
         
     @classmethod
     def default_certif(cls):
         Certification = Pool().get('purchase.certification')
         certification = Certification.search(['id','>',0])
         if certification:
-            return certification[0]
+            return certification[0].id
         
     @classmethod
     def default_certif(cls):
         Association = Pool().get('purchase.association')
         association = Association.search(['id','>',0])
         if association:
-            return association[0]
+            return association[0].id
     
     @classmethod
     def default_tol_min(cls):