Neo4j 1 to 1 Relationship

Question

I have two nodes, "client" and "builder". I want to find only the relationships where the client only has 1 builder, and that builder only has that one client so a 1-1 relationship. So far my query is

MERGE(b:Person{name:csv.name) 
MERGE(c:Person{name:csv.name})
WITH collect(distinct b) as builder, collect(distinct c) as client
UNWIND builder as builders
UNWIND client as clients
WITH builders, clients
WHERE builders = 1 and clients = 1
MATCH (builders:Person)-[bu:builder_for]->(clients:Person)
WITH builders,clients, count(distinct bu) as builds
WHERE builds=1

RETURN distinct builders, clients

This only returns though a 1 to many relationship and is still showing duplicates in my client list.

The highlighted are the ones I would want to return

UPDATE cybersam implementation worked, thank you so much!

Answer 1

Assuming you want to get all the builder / client pairs that only have a single builder_for relationship between them, this query uses the aggregating function COUNT to do that:

MATCH (builder:Person)-[rel:builder_for]->(client:Person)
WITH builder, client, COUNT(rel) AS rel_count
WHERE rel_count = 1
RETURN builder, client;

[UPDATE]

If, instead, you want builder / client pairs in which the builder has only that one client , and vice versa, then this query should work:

MATCH (builder:Person)
WHERE SIZE((builder)-[:builder_for]->()) = 1
MATCH (builder)-[:builder_for]->(client:Person)
WHERE SIZE(()-[:builder_for]->(client)) = 1
RETURN builder, client;

This query uses efficient relationship degree-ness checks (in the WHERE clauses) to ensure that the builder and client nodes only have, respectively, a single outgoing or incoming builder_for relationship.