#258 updated the checks in link update for sqlalchemy nodes

aiida/orm/implementation/sqlalchemy/node.py

@@ -17,7 +17,7 @@
 from sqlalchemy.orm.attributes import flag_modified
 
 from aiida.backends.utils import get_automatic_user
-from aiida.backends.sqlalchemy.models.node import DbNode, DbLink, DbPath
+from aiida.backends.sqlalchemy.models.node import DbNode, DbLink
 from aiida.backends.sqlalchemy.models.comment import DbComment
 from aiida.backends.sqlalchemy.models.user import DbUser
 from aiida.backends.sqlalchemy.models.computer import DbComputer
@@ -195,6 +195,7 @@ def _remove_dblink_from(self, label):
 
     def _add_dblink_from(self, src, label=None, link_type=LinkType.UNSPECIFIED):
         from aiida.backends.sqlalchemy import get_scoped_session
+        from aiida.orm.querybuilder import QueryBuilder
         session = get_scoped_session()
         if not isinstance(src, Node):
             raise ValueError("src must be a Node instance")
@@ -217,10 +218,9 @@ def _add_dblink_from(self, src, label=None, link_type=LinkType.UNSPECIFIED):
         # I am linking src->self; a loop would be created if a DbPath exists
         # already in the TC table from self to src
         if link_type is LinkType.CREATE or link_type is LinkType.INPUT:
-            c = session.query(literal(True)).filter(DbPath.query
-                                                .filter_by(parent_id=self.dbnode.id, child_id=src.dbnode.id)
-                                                .exists()).scalar()
-            if c:
+            if QueryBuilder().append(
+                    Node, filters={'id':self.pk}, tag='parent').append(
+                    Node, filters={'id':src.pk}, tag='child', descendant_of='parent').count() > 0:
                 raise ValueError(
                     "The link you are attempting to create would generate a loop")