No support for Multi-label nodes

[datanostra]

Hi,

I'm working on a graph db benchmark and I have a specific use case that might often occurred which is : create an edge without knowing the type of the source or the target nodes.

I can make it works using inheritance in SQL, creating a Node type, which is extended by all my types :

Create types :
CREATE VERTEX TYPE Node;
CREATE VERTEX TYPE Transaction EXTENDS Node;
CREATE VERTEX TYPE City EXTENDS Node;

Create Nodes :
INSERT INTO Transaction set id = "A"
INSERT INTO City set id = "B"

Then I can query my ingested objects without knowing if they are of types Transaction or City :

• SELECT FROM Node WHERE id = 'id_source'
• CREATE EDGE Relation_Type FROM (SELECT FROM Node WHERE id = 'A') TO (SELECT FROM Node WHERE id = 'B') IF NOT EXISTS

Nevertheless, I would like to be able to create the same mechanism with Cypher.

The problems are :

• the inheritance does not seem replicated to the graph model and then not accessible via Cypher.
• multi-label mechanism does not seem available in ArcadDB. For example, this CYPHER query is not working : CREATE (n:Transaction:Node {id: 'some_id'})
• Unlabeled Cypher queries does not seem to be scalable (MATCH (n) WHERE n.id = "some_id" RETURN n). One reason of this is that we can't benefit from indexes to get optimized access to nodes.

[datanostra]

Ok, I got my answer I guess as I tried to ingest multi-label nodes:
CREATE (n:Person:Node {name: 'Andy', title: 'Developer'})

This triggers the error:

Caused by: org.opencypher.gremlin.translation.exception.SyntaxException: Multiple labels are not supported: Person::Node
        at org.opencypher.gremlin.translation.ir.TranslationWriter$.$anonfun$write$4(TranslationWriter.scala:57)
        at scala.Option.foreach(Option.scala:257)
        at org.opencypher.gremlin.translation.ir.TranslationWriter$.$anonfun$write$3(TranslationWriter.scala:57)
        at org.opencypher.gremlin.translation.ir.TranslationWriter$.$anonfun$write$3$adapted(TranslationWriter.scala:56)
        at scala.collection.TraversableLike$WithFilter.$anonfun$foreach$1(TraversableLike.scala:788)
        at scala.collection.immutable.Map$Map2.foreach(Map.scala:156)
        at scala.collection.TraversableLike$WithFilter.foreach(TraversableLike.scala:787)
        at org.opencypher.gremlin.translation.ir.TranslationWriter$.write(TranslationWriter.scala:56)
        at org.opencypher.gremlin.translation.CypherAst.buildTranslation(CypherAst.scala:120)
        at org.opencypher.gremlin.translation.TranslationFacade.toGremlinGroovy(TranslationFacade.java:56)
        at org.apache.tinkerpop.gremlin.arcadedb.structure.ArcadeCypher.compileToGremlin(ArcadeCypher.java:102)
        at org.apache.tinkerpop.gremlin.arcadedb.structure.ArcadeCypher.<init>(ArcadeCypher.java:53)
        at org.apache.tinkerpop.gremlin.arcadedb.structure.ArcadeGraph.cypher(ArcadeGraph.java:137)
        at com.arcadedb.gremlin.query.CypherQueryEngine.command(CypherQueryEngine.java:64)

[lvca]

@datanostra that's correct, there is no support for multiple labels as Neo4j does. But the inheritance should work because Cypher doesn't know anything about it, it just passes the query by label (= type) through ArcadeDB.

[datanostra]

Thanks for this confirmation on multi-label 👍

I have just retried to query a parent type from Cypher, and again I have an empty result, where I get nodes using the child type as a label in my cypher query.

Here is a scenario:

CREATE VERTEX TYPE Node
CREATE VERTEX TYPE Transaction EXTENDS Node
INSERT INTO Transaction set id = "A"

These queries are working:

SELECT FROM Transaction WHERE id = 'A'
SELECT FROM Node WHERE id = 'A'
MATCH (n:Transaction) WHERE n.id = "A" RETURN n

But this one is not giving any result:
MATCH (n:Node) WHERE n.id = "A" RETURN n

[lvca]

Reproduced, creating a new issue from this discussion.

[lvca]

Fixed in #384.