Data Modification

Modifying existing data with SET, DELETE, REMOVE, and MERGE.

SET

Updates properties on nodes and relationships.

Set Single Property

// Set one property
MATCH (p:Person {name: 'Alice'})
SET p.age = 31

Set Multiple Properties

// Set multiple properties
MATCH (p:Person {name: 'Alice'})
SET p.city = 'NYC', p.country = 'USA'

Set from Map

// Replace all properties using =
MATCH (p:Person {name: 'Alice'})
SET p = {name: 'Alice', age: 31, city: 'NYC'}

// This removes all other properties!

Add/Update Properties with +=

// Merge properties (add new, update existing, keep others)
MATCH (p:Person {name: 'Alice'})
SET p += {city: 'NYC', department: 'Engineering'}

Set with Expression

// Increment value
MATCH (p:Person {name: 'Alice'})
SET p.loginCount = p.loginCount + 1

// Set from calculation
MATCH (p:Person)
SET p.ageNextYear = p.age + 1

Set with CREATE/MATCH

// Create and set in one
CREATE (p:Person)
SET p.name = 'Bob', p.age = 25

DELETE

Removes nodes and relationships.

Delete Relationship

// Delete specific relationship
MATCH (a:Person {name: 'Alice'})-[r:KNOWS]->(b:Person {name: 'Bob'})
DELETE r

Delete Node

// Delete node (must detach relationships first)
MATCH (p:Person {name: 'Alice'})
DELETE p

DETACH DELETE

// Delete node and all its relationships
MATCH (p:Person {name: 'Alice'})
DETACH DELETE p

Delete Multiple

// Delete multiple items
MATCH (p:Person {name: 'Alice'})-[r]-(), (p)
DELETE r, p

REMOVE

Removes labels and properties.

Remove Property

// Remove single property
MATCH (p:Person {name: 'Alice'})
REMOVE p.temporary

// Remove multiple properties
MATCH (p:Person {name: 'Alice'})
REMOVE p.temp1, p.temp2

Remove Label

// Remove single label
MATCH (p:Person:Employee {name: 'Alice'})
REMOVE p:Employee

// Remove multiple labels
MATCH (p:Person:Employee:Manager {name: 'Alice'})
REMOVE p:Employee, p:Manager
// Now p only has :Person label

Remove All Labels

MATCH (p:Person {name: 'Alice'})
REMOVE p:Person
// Node now has no labels

MERGE

Finds existing patterns or creates them if not found.

Basic MERGE

// Find or create node
MERGE (p:Person {email: 'alice@example.com'})
RETURN p

MERGE with ON CREATE

// Set properties only when creating
MERGE (p:Person {email: 'alice@example.com'})
ON CREATE SET
  p.name = 'Alice',
  p.createdAt = datetime(),
  p.active = true
RETURN p

MERGE with ON MATCH

// Update properties only when existing
MERGE (p:Person {email: 'alice@example.com'})
ON MATCH SET
  p.lastSeen = datetime(),
  p.visitCount = p.visitCount + 1
RETURN p

Combined ON CREATE and ON MATCH

MERGE (p:Person {email: 'alice@example.com'})
ON CREATE SET
  p.name = 'Alice',
  p.createdAt = datetime()
ON MATCH SET
  p.lastSeen = datetime()
RETURN p

MERGE Relationship

// Find or create relationship
MATCH (a:Person {name: 'Alice'}), (b:Person {name: 'Bob'})
MERGE (a)-[r:KNOWS]->(b)
RETURN r

// With properties
MATCH (a:Person {name: 'Alice'}), (b:Person {name: 'Bob'})
MERGE (a)-[r:KNOWS]->(b)
ON CREATE SET r.since = 2020
RETURN r

MERGE Path

// Create entire path if not exists
MERGE (a:Person {name: 'Alice'})-[:KNOWS]->(b:Person {name: 'Bob'})
RETURN a, b

MERGE with Multiple Patterns

// Match/create both nodes and relationship
MERGE (a:Person {email: 'alice@example.com'})
MERGE (b:Person {email: 'bob@example.com'})
MERGE (a)-[:KNOWS]->(b)

FOREACH

Iterate over a list and perform operations.

// Set property on each element
MATCH (p:Person {name: 'Alice'})
FOREACH (tag IN ['developer', 'python', 'database'] |
  CREATE (t:Tag {name: tag})
  MERGE (p)-[:INTERESTED_IN]->(t)
)

Common Patterns

Upsert Pattern

// Update or insert (upsert)
MERGE (p:Person {email: $email})
ON CREATE SET
  p.name = $name,
  p.createdAt = datetime(),
  p.version = 1
ON MATCH SET
  p.name = $name,
  p.updatedAt = datetime(),
  p.version = p.version + 1
RETURN p

Soft Delete

// Instead of DELETE, mark as inactive
MATCH (p:Person {name: 'Alice'})
SET p.active = false, p.deletedAt = datetime()
REMOVE p:Active

Bulk Update

// Update many nodes at once
MATCH (p:Person)
WHERE p.lastLogin < datetime() - duration('P1Y')
SET p.status = 'inactive'

Property Migration

// Rename property
MATCH (p:Person)
WHERE EXISTS(p.oldName)
SET p.newName = p.oldName
REMOVE p.oldName