How to persist a List as a property of a node?

Question

I am trying to persist a list of objects of a class suppose xyz. when I do this in the NodeEntity Class:

@Property
List<xyz> listOfConditions

The Node table when loaded from the neo4j-database via the Neo4jOperations.load(entity) method, will return an error saying :- ERROR mapping GraphModel to NodeEntity type class.

Is there any way to persist a List of Objects onto a nodes properties in Neo4j?. I am using neo4j-ogm-embedded driver and Spring-data-neo4j.

Answer 1

Neo4j does not support storing another object as a nested property. Neo4j-OGM only supports

any primitive, boxed primitive or String or arrays thereof, essentially anything that naturally fits into a Neo4j node property.

If you want to work around that, you may need to create a custom type convertor. For example,

import org.neo4j.ogm.typeconversion.AttributeConverter

class XYZ{
    XYZ(Integer x, String y) {
        this.x = x
        this.y = y
    }
    Integer x
    String y
}

public class XYZConverter implements AttributeConverter<XYZ, String> {

    @Override
    public String toGraphProperty(XYZ value) {
        return value.x.toString() + "!@#" + value.y
    }

    @Override
    public XYZ toEntityAttribute(String value) {
        String[] split = value.split("!@#")
        return new XYZ(Integer.valueOf(split[0]), split[1])
    }
}

You can then annotate the @NodeEntity with a @Convert like this

@NodeEntity
class Node {
    @GraphId
    Long id;

    @Property
    String name

    @Convert(value = XYZConverter.class)
    XYZ xyz
}

On the flip side, its not a good practice to do this, since ideally you should link Node and XYZ with a 'hasA' relationship. Neo4j has been designed to optimally handle such kind of relationships, so it would be best to play with to strengths of neo4j

Answer 2

No, nested objects represented as properties on a single node are not supported by the OGM. The only option is to write a custom converter to serialize the nested object to a String representation and store it as a single property.

Otherwise, a list of objects on a node is treated as relationships from the node to those objects.

Here's a link to the manual for further reference: http://neo4j.com/docs/ogm-manual/current/