CODEWITHSUNDEEP
neo4jcypher
firemancer
firemancer

Reputation: 27

Neo4j query for getting multiple connected nodes

In my graph, I want to get the first-degree, second-degree, and third-degree neighbors of a certain node. If my graph is A -> B -> C -> D -> E, then

When checking neighbors, I go in the reverse direction of the edge. To get these nodes, I wrote the following query.

MATCH (changedNode: Function) WHERE changedNode.signature IN [...]
MATCH (neig1: Function)-[:CALLS]->(changedNode)
MATCH (neig2: Function)-[:CALLS]->(neig1)
MATCH (neig3: Function)-[:CALLS]->(neig2)
RETURN DISTINCT neig1.functionName, neig2.functionName,  neig3.functionName

I realized that this code does not return B as the first-degree neighbor of C since A does not have any neighbors(neig3 is empty). In other words, this query requires a node to have a third-degree neighbor. I understood this but could not update my code. How should I revise my query?

Upvotes: 1

Views: 156

Answers (2)

Nimra Tahir
Nimra Tahir

Reputation: 1

Use of OPTIONAL MATCH matches patterns against your graph database, just like a MATCH does. The difference is that if no matches are found, OPTIONAL MATCH will use a null for missing parts of the pattern. OPTIONAL MATCH could be considered the Cypher equivalent of the outer join in SQL.

MATCH (changedNode: Function) WHERE changedNode.signature IN [...]
MATCH (neig1: Function)-[:CALLS]->(changedNode)
OPTIONAL MATCH (neig2: Function)-[:CALLS]->(neig1)
OPTIONAL MATCH (neig3: Function)-[:CALLS]->(neig2)
RETURN DISTINCT neig1.functionName, neig2.functionName, neig3.functionName

For more explanation, visit: https://neo4j.com/developer/kb/a-note-on-optional-matches/

Upvotes: 0

jose_bacoy
jose_bacoy

Reputation: 12704

You can use OPTIONAL MATCH since A may not have a neighbor. Then the query will return a null value for neigh3.

MATCH (changedNode: Function) WHERE changedNode.signature IN [...]
MATCH (neig1: Function)-[:CALLS]->(changedNode)
OPTIONAL MATCH (neig2: Function)-[:CALLS]->(neig1)
OPTIONAL MATCH (neig3: Function)-[:CALLS]->(neig2)
RETURN DISTINCT neig1.functionName, neig2.functionName,  neig3.functionName

Upvotes: 1

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