--- a/cubicweb/server/querier.py	Thu Nov 30 11:00:01 2017 +0100
+++ b/cubicweb/server/querier.py	Thu Nov 30 11:55:35 2017 +0100
@@ -347,6 +347,8 @@
     def add_relation_def(self, rdef):
         """add an relation definition to build"""
         edef, rtype, value = rdef
+        if self.schema[rtype].rule:
+            raise QueryError("'%s' is a computed relation" % rtype)
         self.r_defs.add(rdef)
         if not isinstance(edef, int):
             self._r_subj_index.setdefault(edef, []).append(rdef)