Fallback to secondary query if first fails to match

[wheresrhys]

I have a model a bit like this:

(:Budget)-[:PAYS_FOR]->(:System)-[:DELIVERED_BY]->(:Team)<-[:PAYS_FOR]-(:Budget)

Most Systems do not have a direct budget associated because most are funded via a team, but where the direct relationship is specified it takes precedence, falling back to the team Budget where the direct Budget is not defined

I'm struggling to write a query which has this fallback behaviour.

In pseudo code I want:

try {
    MATCH (b:Budget)-[:PAYS_FOR]->(s:System)
    WHERE s.code = "my-code"
    RETURN b
} catch {
    MATCH (b:Budget)-[:PAYS_FOR]->(:Team)<-[:DELIVERED_BY]-(s:System)
    WHERE s.code = "my-code"
    RETURN b
}

How do achieve such conditional choice of query?

[12kunal34]

Hi @wheresrhys ,

Yeah we can do that . for this you need to use below apoc procedure . this will work as if else .

apoc would be like this.

OPTIONAL MATCH (b:Budget)-[:PAYS_FOR]->(s:System) WHERE s.code = "my-code"with b
CALL apoc.when(b IS NOT NULL,"MATCH (b:Budget)-[:PAYS_FOR]->(s:System) WHERE s.code = 'my-code'RETURN b" ,"MATCH (b:Budget)-[:PAYS_FOR]->(:Team)<-[:DELIVERED_BY]-(s:System) WHERE s.code = 'my-code' RETURN b") yield value
Return value

Please run and let us know this is solving your query or not.

[wheresrhys]

Thanks Kunal.

I'm surprised it's not possible without APOC though.

Reading the solution you give, it looks like it executes the initial query twice in the case where the PAYS_FOR relationship exists on the System node. Is there some way to just reuse the reslt of the original query?

[michael_hunger]

Usually you would do that on the client side.

You can probably also try to use UNION with the two statements

[wheresrhys]

The client is neo4j-graphql-js, and I'd like to use the @cypher directive to populate this field in get requests

[michael_hunger]

Hmm ok, would you mind creating an issue in APOC so we can look into thatt