Use different hash for records without id

In order to have store them efficiently in dictionary, we generate a different
hash for each unsaved record by using the instance id.

issue9240
review295421002

trytond/model/model.py

@@ -316,7 +316,7 @@ class Model(URLMixin, PoolBase, metaclass=ModelMeta):
         return not self == other
 
     def __hash__(self):
-        return hash((self.__name__, self.id))
+        return hash((self.__name__, id(self) if self.id is None else self.id))
 
     def __bool__(self):
         return True

trytond/tests/test_model.py

@@ -30,6 +30,30 @@ class ModelTestCase(unittest.TestCase):
         self.assertEqual(
             repr(record), "Pool().get('test.model')(%s)" % record.id)
 
+    @with_transaction()
+    def test_hash_with_id(self):
+        "Test hash with id"
+        pool = Pool()
+        Model = pool.get('test.model')
+
+        record1 = Model(id=1)
+        record1bis = Model(id=1)
+        record2 = Model(id=2)
+
+        self.assertEqual(hash(record1), hash(record1bis))
+        self.assertNotEqual(hash(record1), hash(record2))
+
+    @with_transaction()
+    def test_hash_without_id(self):
+        "Test hash without id"
+        pool = Pool()
+        Model = pool.get('test.model')
+
+        record1 = Model()
+        record2 = Model()
+
+        self.assertNotEqual(hash(record1), hash(record2))
+
     @with_transaction()
     def test_init_parent(self):
         "Test __init__ with _parent_"