Cypher Neo4j在两个节点之间创建关系并避免双向关系

Question

Here is my query:

   MATCH (a:Person)-[:friend]->(p:Person)<-[:friend]-(b:Person)
   WITH a, b, COUNT(p) as count
   WHERE count >= 2
   CREATE (a)-[:friend {new: "yes"}]->(b)
   RETURN a,b,count

I tried to find a and b that have at least 2 common friends and creating friend relationship between them. Here is the result sample:

   a             b            count
   name1         name2          3
   name2         name1          3

Notes that the result is repeated, and this will create a bi-directional relationship between them. name1-[:friend]->name2 also means name1<-[:friend]-name2, so if I created a bi-directional relationship, the relationship between them will be duplicated as shown in my csv file:

   a             b            relationship
   name1         name2           friend
   name1         name2           friend
   name2         name2           friend
   name2         name2           friend

Is there any way I can avoid this? Thank you for your time.

Answer 1

Yeah, there's a trick to do this:

MATCH (a:Person)-[:friend]->(p:Person)<-[:friend]-(b:Person)
WHERE ID(a) < ID(b)
WITH a, b, COUNT(p) as count
WHERE count >= 2
CREATE (a)-[:friend {new: "yes"}]->(b)
RETURN a,b,count

The change is the WHERE ID(a) < ID(b) which makes sure that just one of the two directions is chosen