Efficient way to create relationships in neo4j

Question

I have a neo4j database populated with thousands of nodes without any relationship defined. I have a file which contains relationships between nodes, so I would like to create relationships between these nodes created in the database. My current approach is:

from py2neo import NodeSelector,Graph,Node,Relationship
graph = Graph('http://127.0.0.1:7474/db/data')
tx = graph.begin()
selector = NodeSelector(graph)
with open("file","r") as relations:
    for line in relations:
        line_split=line.split(";")
        node1 = selector.select("Node",unique_name=line_split[0]).first()
        node2 = selector.select("Node",unique_name=line_split[1]).first()
        rs = Relationship(node1,"Relates to",node2)
        tx.create(rs)
tx.commit()

The current approach needs 2 queries to database in order to obtain nodes to form a relationship + relationship creation. Is there a more efficient way given that nodes currently exist in the database?

You could create a single string for the Cypher query then [Graph.run](http://py2neo.org/v3/database.html#py2neo.database.Graph.run) it. — jonrsharpe, Mar 22 '18 at 08:40

score 2 · Accepted Answer · answered Mar 22 '18 at 08:48

You can use some form of node caching while populating relations:

from py2neo import NodeSelector,Graph,Node,Relationship
graph = Graph('http://127.0.0.1:7474/db/data')
tx = graph.begin()
selector = NodeSelector(graph)
node_cache = {}

with open("file","r") as relations:
    for line in relations:
        line_split=line.split(";")

        # Check if we have this node in the cache
        if line_split[0] in node_cache:
            node1 = node_cache[line_split[0]]
        else:
            # Query and store for later
            node1 = selector.select("Node",unique_name=line_split[0]).first()
            node_cache[line_split[0]] = node1

        if line_split[1] in node_cache:
            node2 = node_cache[line_split[1]]
        else:
            node2 = selector.select("Node",unique_name=line_split[1]).first()
            node_cache[line_split[1]] = node2

        rs = Relationship(node1,"Relates to",node2)
        tx.create(rs)

tx.commit()

With the above you will only load each node once and only if that node appears in your input file.

Efficient way to create relationships in neo4j

1 Answers1