py2neo, neo4j: How to create relation between two existing node

Question

I am following this tutorial to access neo4j db using python. According to this tutorial I have created 2 relations among 4 nodes. The code is given below

alice, bob, rel = graph_db.create(
                      {"name": "Alice"}, {"name": "Bob"},
                      (0, "KNOWS", 1))
dev, carol, rel = graph_db.create(
                      {"name": "Dev"}, {"name": "Carol Smith"},
                      (0, "KNOWS", 1))

How can I create relation between alice and carol without creating new node?

Following code snippet is given in that tutorial to create relation between existing node. Not sure how to use how to use this in above case.

ref_node = graph_db.get_reference_node()
alice, rel = graph_db.create(
                {"name": "Alice"}, (ref_node, "PERSON", 0))

When I try to execute

ref_node = graph_db.get_reference_node()

I get the following error.

Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'GraphDatabaseService' object has no attribute 'get_reference_node'

Any suggestion to solve this issue?

score 9 · Accepted Answer · answered May 02 '14 at 13:30

I tried the following and got the results I think you want:

from py2neo import neo4j, node, rel

graph = neo4j.GraphDatabaseService("http://localhost:7474/db/data/")

alice, = graph.create(node(name="Alice")) # Comma unpacks length-1 tuple.
bob, = graph.create(node(name="Bob"))
carol, = graph.create(node(name="Carol Smith"))
dev, = graph.create(node(name="Dev"))

graph.create(rel(alice, "KNOWS", bob))
graph.create(rel(dev, "KNOWS", carol))
graph.create(rel(alice, "KNOWS", carol))

My graph now looks like this in the browser:

enter image description here

Alternatively, you can create the graph in one graph.create() statement:

from py2neo import neo4j, node, rel

graph = neo4j.GraphDatabaseService("http://localhost:7474/db/data/")

graph.create(
    node(name="Alice"),       #0
    node(name="Bob"),         #1
    node(name="Carol Smith"), #2
    node(name="Dev"),         #3
    rel(0, "KNOWS", 1),
    rel(3, "KNOWS", 2),
    rel(0, "KNOWS", 2)
)

And the output is the same. Hope this helps.

One more thing, how can I visualize the graph? Is there any tool available? — Quazi Marufur Rahman, May 02 '14 at 16:33
I would jump into the browser. That's the best way to get the visuals. — Nicole White, May 02 '14 at 17:01
you're creating new nodes and creating relations between them.. how do you create relationship to an existing node? that is what get_reference_node() is for and it is giving out exceptions — Kiran Vemuri, Aug 15 '14 at 01:33

score 2 · Answer 2 · answered May 03 '14 at 08:43

2

The reference node was a feature included in earlier versions of Neo4j and, by extension, py2neo. It has since been deprecated and removed so I should have also removed all traces from the py2neo documentation - it appears I've missed one!

Thanks for pointing this out, I'll add myself a task to get this page up to date.

In terms of creating a relationship, Nicole's answer is spot on and should have all the information you need.

answered May 03 '14 at 08:43

Nigel Small

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Hello Nigel, if get_reference_node is deprecated , how do i create a relation between a new node and an existing node from py2neo? – Kiran Vemuri Aug 15 '14 at 01:35
2

i want to do something like this: MATCH (actor:Actor) WHERE actor.name = "Tom Hanks" CREATE (movie:Movie { title:'Sleepless IN Seattle' }) CREATE (actor)-[:ACTED_IN]->(movie); – Kiran Vemuri Aug 15 '14 at 01:49
Looks like that Cypher should already probably work. Best idea is to try it out in the browser (http://localhost:7474/browser) and pop up a new StackOverflow question if you hit a specific problem. – Nigel Small Aug 15 '14 at 16:23

py2neo, neo4j: How to create relation between two existing node

2 Answers2