Defining a schema

This guide explains how to define a schema by using indexes and constraints. While Neo4j is often described as schema optional, indexes and constraints can be added when needed, either for performance optimization or modeling benefits.

Example graph

Use the following example graph to follow the guide.

CREATE (forrestGump:Movie {title: 'Forrest Gump', released: 1994})
CREATE (robert:Person:Director {name: 'Robert Zemeckis', born: 1951})
CREATE (tom:Person:Actor {name: 'Tom Hanks', born: 1956})
CREATE (tom)-[:ACTED_IN {roles: ['Forrest']}]->(forrestGump)
CREATE (robert)-[:DIRECTED]->(forrestGump)

This is the resulting graph:

Using indexes

Indexes are used for speeding up data retrieval and thus improve performance. They can be added at any time.

The following query creates an index to facilitate finding actors by name in the database:

CREATE INDEX example_index_1 FOR (a:Actor) ON (a.name)

Cypher®'s query planner automatically selects the appropriate index to use for your query. Only in exceptional cases do you need to specify which index to use. See Cypher → Index hints for the Cypher planner for more information.

For example, the following query automatically uses the example_index_1 previously created:

MATCH (actor:Actor {name: 'Tom Hanks'})
RETURN actor

The result is:

actor

actor
`(:Person:Actor {born: 1956, name: "Tom Hanks"})`
Rows: 1

(:Person:Actor {born: 1956, name: "Tom Hanks"})

Rows: 1

Composite index

A composite index is an index on multiple properties for all nodes that have a particular label. For example, the following statement creates a composite index on all nodes labeled with Actor and which have both a name and a born property:

CREATE INDEX example_index_2 FOR (a:Actor) ON (a.name, a.born)

Note that, for example, if you had a node with the Actor label that did not contain the born property, it wouldn’t be indexed.

Show indexes

You can use SHOW INDEXES to list indexes in a database:

SHOW INDEXES

With the current example dataset, the result is:

id name state populationPercent type entityType labelsOrTypes properties indexProvider owningConstraint lastRead readCount

id	name	state	populationPercent	type	entityType	labelsOrTypes	properties	indexProvider	owningConstraint	lastRead	readCount
`1`	`"index_1b9dcc97"`	`"ONLINE"`	`100.0`	`"LOOKUP"`	`"RELATIONSHIP"`	`null`	`null`	`"token-lookup-1.0"`	`null`	`null`	`0`
`0`	`"index_460996c0"`	`"ONLINE"`	`100.0`	`"LOOKUP"`	`"RELATIONSHIP"`	`null`	`null`	`"token-lookup-1.0"`	`null`	`null`	`0`
Rows: 2

1

"index_1b9dcc97"

"ONLINE"

100.0

"LOOKUP"

"RELATIONSHIP"

null

"token-lookup-1.0"

null

0

"index_460996c0"

"ONLINE"

100.0

"LOOKUP"

"RELATIONSHIP"

null

"token-lookup-1.0"

null

0

Rows: 2

Using constraints

Constraints are used to make sure that the data adheres to the rules of the domain. They can be property uniqueness, property existence, property type, or key constraints.

Constraint type	Description
Property uniqueness	Ensure that the combined property values are unique for all nodes with a specific label or all relationships with a specific type.
Property existence	Ensure that a property exists either for all nodes with a specific label or for all relationships with a specific type. Enterprise Edition
Property type	Ensure that a property has the required property type for all nodes with a specific label or for all relationships with a specific type. Enterprise Edition
Key	Ensure that all properties exist and that the combined property values are unique for all nodes with a specific label or all relationships with a specific type. Enterprise Edition

Constraint type

Description

Property uniqueness

Ensure that the combined property values are unique for all nodes with a specific label or all relationships with a specific type.

Property existence

Ensure that a property exists either for all nodes with a specific label or for all relationships with a specific type. Enterprise Edition

Property type

Ensure that a property has the required property type for all nodes with a specific label or for all relationships with a specific type. Enterprise Edition

Key

Ensure that all properties exist and that the combined property values are unique for all nodes with a specific label or all relationships with a specific type. Enterprise Edition

Constraints can be added to the database at any time. It’s recommended to do it early (or even when the database is still empty), since adding constraints requires that the existing data complies with the constraint that is being added.

This is an example of how to create a constraint:

CREATE CONSTRAINT constraint_example_1 FOR (movie:Movie) REQUIRE movie.title IS UNIQUE

Show constraints

You can use SHOW CONSTRAINTS to find all existing constraints in a graph:

SHOW CONSTRAINTS

With the current example, this is the result you get:

id name type entityType labelsOrTypes properties ownedIndex propertyType

id	name	type	entityType	labelsOrTypes	properties	ownedIndex	propertyType
`5`	`"constraint_example_1"`	`"UNIQUENESS"`	`"NODE"`	`["Movie"]`	`["title"]`	`"constraint_example_1"`	`null`
Rows: 1

5

"constraint_example_1"

"UNIQUENESS"

"NODE"

["Movie"]

["title"]

"constraint_example_1"

null

Rows: 1

Keep learning

Refer to the Cypher documentation for more information on indexes and constraints:

Search-performance indexes → See how to get quicker retrievals of exact matches between an index and the primary data storage.
Semantic indexes → Read more on how semantic indexes capture the semantic meaning or context of the data in a database.
Create, show, and drop indexes → Discover how to create, show, and drop indexes.
Create, show, and drop constraints → Learn how to create, show, and drop constraints.