Neo4j Schema Enforcer extension

This is a Neo4j Kernel Extension that allows you to enforce certain schema on graph nodes and edges.

Since it is Neo4j already supports property existence constraints, this plugin only validates, that properties are of same type as specified node schema definition.

How does it work?

This extension is a custom TransactionEventHandler. It does not validates existing nodes, but prevents adding of new properties to nodes if they are of invalid type.

Installation

• Clone this repository and run mvn install

• Copy target/neo4j.schema_enforcer-0.0.1-SNAPSHOT.jar to plugins folder in Neo4j installation folder

• Restart Neo4j

Node Schemas

Schemas are stored in nodes with Metadata label.

Each node defining schema should have following properties:

• label - label of target nodes or relationships on which schema should be enforced

• schema - definition of schema for nodes having the same label as the one in label property

It is highly advised to create an unique constraint on Metadata.label property:

CREATE CONSTRAINT ON (m:Metadata) ASSERT m.label IS UNIQUE

Schema definition is stored as collection of strings where each element specifies type of one property in following format: propertyName:propertyType.

Supported property types:

• bool - boolean values

• int - integers

• number - integers or floating point numbers

• string - strings

• array[bool] - collection of boolean values

• array[int] - collection of integers

• array[number] - collection of integers or floating point numbers

• array[string] - collection of strings

Example Node Schema

This statement will create example schema definition for Book nodes.

CREATE (m:Metadata)
    SET m.label = 'Book',
        m.schema = [
            'title:string',
            'price:number',
            'pages:int',
            'available:bool',
            'reviews:array[string]'
        ]
RETURN m

You may add adding adding new Book nodes:

CREATE (b:Book) SET b.title = 'The Book', b.price = 9.99, b.reviews = ['Best book ever!', 'I recommend it!'] RETURN b

However if you attept to add a Book node with properties that do not conform with given schema:

CREATE (b:Book) SET b.title = 'Yet Another Book', b.price = 'free', b.pages = 3.14159, b.reviews = [2,3,1] RETURN b

transaction will be rolled back (provided that Schema Enforcer is correctly installed).