model: adding two missing possibilities for ValueListParameter (#292)

* from https://sap.github.io/odata-vocabularies/vocabularies/Common.html

Author: frij-aws

pyodata/v2/model.py

@@ -2491,7 +2491,7 @@ def from_etree(target, annotation_node):
 
 
 class ValueHelperParameter:
-    Direction = Enum('Direction', 'In InOut Out DisplayOnly FilterOnly')
+    Direction = Enum('Direction', 'In InOut Out DisplayOnly FilterOnly Constant Constants')
 
     def __init__(self, direction, local_property_name, list_property_name):
         super(ValueHelperParameter, self).__init__()
@@ -2697,7 +2697,9 @@ def sap_attribute_get_bool(node, attr, default):
     'com.sap.vocabularies.Common.v1.ValueListParameterInOut': ValueHelperParameter.Direction.InOut,
     'com.sap.vocabularies.Common.v1.ValueListParameterOut': ValueHelperParameter.Direction.Out,
     'com.sap.vocabularies.Common.v1.ValueListParameterDisplayOnly': ValueHelperParameter.Direction.DisplayOnly,
-    'com.sap.vocabularies.Common.v1.ValueListParameterFilterOnly': ValueHelperParameter.Direction.FilterOnly
+    'com.sap.vocabularies.Common.v1.ValueListParameterFilterOnly': ValueHelperParameter.Direction.FilterOnly,
+    'com.sap.vocabularies.Common.v1.ValueListParameterConstant': ValueHelperParameter.Direction.Constant,
+    'com.sap.vocabularies.Common.v1.ValueListParameterConstants': ValueHelperParameter.Direction.Constants
 }