Update __init__.py

iyp/__init__.py

@@ -558,7 +558,28 @@ def add_links(self, src_node, links):
 
         self.tx.run(matches + where + merges).consume()
         self.commit()
-
+
+    def add_relationship_properties(
+            self,
+            node_label_properties,
+            relationship,
+            connected_node_label_properties,
+            properties):
+        """The function goes through each provided property and adds it to the
+        relationship between the specified nodes, but only if that property doesn't
+        already exist in the relationship."""
+        property_setters = ','.join([f'rel.{prop} = ${{props}}.${{prop}}' for prop in properties.keys()])
+        add_query = f"""
+            MATCH (node1:{node_label_properties})-[rel:{relationship}]-(node2:{connected_node_label_properties})
+            WITH rel
+            UNWIND keys($properties) AS prop
+            WHERE NOT EXISTS(rel[prop])
+            SET {property_setters}
+            """
+        res = self.tx.run(add_query, properties=properties)
+        res.consume()
+        self.commit()
+
     def batch_add_properties(self, id_prop_list):
         """Add properties to existing nodes.