Neo4j

MERGE Trap

• MERGE matches the FULL pattern—MERGE (a)-[:KNOWS]->(b) creates duplicates if relationship missing
• Safe upsert: merge nodes separately, then merge relationship
• Use ON CREATE SET and ON MATCH SET for conditional properties—without these, nothing updates on match
• For simple node upsert: MERGE (n:User {id: $id}) with unique constraint on id

Indexes

• No index on property = full label scan—always index properties used in WHERE
• Unique constraint auto-creates index—prefer constraint over plain index when applicable
• Check plan with EXPLAIN before production—look for "NodeByLabelScan" without filter pushdown
• Text search needs full-text index: CREATE FULLTEXT INDEX FOR (n:Post) ON EACH [n.title, n.body]

Variable-Length Paths