Create multiple nodes and relationships in several Cypher statements

Question

I want to create multiple neo4j nodes and relationships in one Cypher transaction. I'm using py2neo which allows issuing multiple Cypher statements in one transaction .

I thought I'd add a statement for each node and relationship I create:

tx.append('CREATE (n:Label { prop: val })')
tx.append('CREATE (m:Label { prop: val2 })')

Now I want to create a relationship between the two created nodes:

tx.append('CREATE (n)-[:REL]->(m)')

This doesn't work as expected. No relationship is created between the first two nodes, since there's no n or m in the context of the last statement (there is a new relationship between two new nodes - four nodes are created in total)

Is there a way around this? Or should I combine all the calls to CREATE (around 100,000 per logical transaction) in one statement?

It just hurts my brain thinking about such a statement, because I'll need to store everything on one big StringIO, and I lose the ability to use Cypher query parameters - I'll need to serialize dictionaries to text myself.

UPDATE: The actual graph layout is more complicated than that. I have multiple relationship types, and each node is connected to at least two other nodes, while some nodes are connected to hundreds of nodes.

It won't fail, it will just create two nodes with no labels or properties. The relationship will still be created. — Nicole White, Dec 09 '15 at 20:37
That's because identifiers are only relevant within the scope of the query: http://stackoverflow.com/a/34074151/2848578 — Nicole White, Dec 09 '15 at 21:01
Yes, I know that, I was hoping there was some way around this without creating one huge query. — zmbq, Dec 09 '15 at 21:02
If you are doing a large data import consider using [`LOAD CSV`](http://neo4j.com/docs/stable/query-load-csv.html). See http://stackoverflow.com/questions/34118491/fastest-way-to-import-to-neo4j/34143376#34143376 for an example. Also see http://stackoverflow.com/questions/34124759/batch-loading-neo4j/34140006#34140006 for an example using py2neo `WriteBatch` — William Lyon, Dec 09 '15 at 21:53
Yes, I think I'll need to go the CSV way for performance reasons, and just forget about transactions. — zmbq, Dec 09 '15 at 21:54

score 2 · Answer 1 · answered Dec 09 '15 at 20:18

2

You don't need multiple queries. You can use a single CREATE to create each relationship and its related nodes:

tx.append('CREATE (:Label { prop: val })-[:REL]->(:Label { prop: val2 })')

answered Dec 09 '15 at 20:18

cybersam

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The example I've given is over-simplified. I have numerous relationships between nodes, I can't create them with one create statement. – zmbq Dec 09 '15 at 20:36

score 0 · Answer 2 · answered Dec 09 '15 at 21:10

Do something like this:

rels = [(1,2), (3,4), (5,6)]

query = """
CREATE (n:Label {prop: {val1} }),
       (m:Label {prop: {val2} }),
       (n)-[:REL]->(m)
"""

tx = graph.cypher.begin()

for val1, val2 in rels:
    tx.append(query, val1=val1, val2=val2)

tx.commit()

And if your data is large enough consider doing this in batches of 5000 or so.

Create multiple nodes and relationships in several Cypher statements

2 Answers2