Awoid duplicate relations in catalog when republishing.

When an object is published for the second time, having the same
relation, it should not be readded to the relation catalog but updated
instead.
By using ``updateRelations`` instead of ``addRelations`` this is handled
correctly by ``z3c.relationfield``.

ftw/publisher/core/adapters/dx_field_data.py

@@ -22,7 +22,7 @@
 else:
     HAS_RELATIONS = True
     from z3c.relationfield import RelationValue
-    from z3c.relationfield.event import addRelations
+    from z3c.relationfield.event import updateRelations
     from z3c.relationfield.interfaces import IRelation
     from z3c.relationfield.interfaces import IRelationChoice
     from z3c.relationfield.interfaces import IRelationList
@@ -92,7 +92,7 @@ def setData(self, data, metadata):
                 setattr(repr, name, value)
 
         if HAS_RELATIONS:
-            addRelations(self.context, None)
+            updateRelations(self.context, None)
 
     def pack(self, name, field, value):
         """Packs the field data and makes it ready for transportation with

ftw/publisher/core/tests/test_dexterity.py

@@ -5,7 +5,6 @@
 from ftw.publisher.core.tests.interfaces import ITextSchema
 from json import dumps
 from json import loads
-from plone import api
 from plone.app.relationfield.behavior import IRelatedItems
 from plone.app.testing import applyProfile
 from plone.app.testing import IntegrationTesting
@@ -171,6 +170,10 @@ def test_relations_with_RelationValue_objects(self):
         self.assertEquals(1, len(target.relatedItems),
                           'Relation missing')
 
+        self._set_field_data(target, data, json=True)
+        self.assertEquals(1, len(target.relatedItems),
+                          'Publishing twice should not add more relations.')
+
         relation, = target.relatedItems
         self.assertEquals(foo, relation.to_object)