def add_rel(self, source_node_id, target_node_id, rel):
        """Add a relationship between nodes.

        Args:
            source_node_id: Node Id for the source node.
            target_node_id: Node Id for the target node.
            rel: Name of the relationship 'contains'
        """

        # Add the relationship
        n1_ref = self.graph_db.get_indexed_node('Node', 'node_id', source_node_id)
        n2_ref = self.graph_db.get_indexed_node('Node', 'node_id', target_node_id)

        # Sanity check
        if not n1_ref or not n2_ref:
            print 'Cannot add relationship between unfound nodes: %s --> %s' % (source_node_id, target_node_id)
            return
        path = neo4j.Path(n1_ref, rel, n2_ref)
        path.get_or_create(self.graph_db)
dataset/ETHPy150Open SuperCowPowers/workbench/workbench/server/neo_db.py/NeoDB.add_rel/original