Deleting a relationship IF a condition is true?

[andre_krosby199]

Just discovered Graph and Neo4j a couple of days ago and I must say I really like what it has to offer. I'm still tinkering around still, and now I wonder how I would proceed with conditions inside queries.
In the below code, how would I delete the relationship in the same query if the quantity is set to 0?

I have a hard time understanding the syntax of the conditionals inside Cypher.

    result = session.run(
        f'MATCH (order:Order {{ ref: "SomeOrder" }})<-[rel:IN_ORDER]-(product:Product {{ name: "SomeProduct" }}) '
        f'SET rel += {{ quantity: 0 }} '
        f'WITH order '
        f'MATCH (order)<-[r:IN_ORDER]-(p:Product) '
        f'RETURN order, p.name, p.price * r.quantity AS total_unit_price '
    )

[MuddyBootsCode]

Hello! Welcome to the community. If that only thing your checking is the quantity on the relationship you can just do:

match(o:Order)<-[r:IN_ORDER]-(p:Product)
where r.quantity = 0
delete r
return o, p

That will check to see that the quantity is zero and if so delete the relationship.

[Cobra]

Hello @andre.krosby1992 and welcome

If there are a lot of relations to delete, the best way to delete is:

CALL apoc.periodic.iterate('MATCH (o:Order)<-[r:IN_ORDER]-(p:Product)
WHERE r.quantity = 0 RETURN r', 'DELETE r', {batchSize:1000})

Regards,
Cobra

[andrew_bowman]

Also you can reference this article if you're looking for more info on conditional Cypher execution:

Neo4j Graph Database Platform

Conditional Cypher Execution - Neo4j Graph Database Platform

At some point you’re going to write a Cypher query requiring some conditional logic, where you want different Cypher statements executed depending on the case. At this point in time Cypher does not include native conditional functionality to address...