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Alex February 2016

Can I write a Neo4j Plugin to intercept and modify CYPHER queries

In my system, I would like to intercept and change Cypher queries as they come in, one alternative is to modify them before sending them from my middle layer to the graph - but is there a way to have a plugin do the conversion for me in the graph itself?

I'd like to do some of the following: If someone identifying themselves as members of group A, imagine I'd like to change their request from:

MATCH(f:Film)-[r:REVIEWED_BY]-(u:User {id:"1337"})


MATCH(p:Product)-[p:PURCHASED_BY]-(u:User {id:"1337"})

Is something like this possible? Or do I have to write the traversals in Java directly to achieve this?


MicTech February 2016

At this time it's not possible to extend or modify Cypher queries.

If you need that I recommend you to use Transaction Event API - http://graphaware.com/neo4j/transactions/2014/07/11/neo4j-transaction-event-api.html

With that you should be able to change what query returns.

Max De Marzi February 2016

Of course you can. You can do ANYTHING in Neo4j. Just grab the cypher string in an unmanaged extension that receives a post request, alter it any way you want, execute it with the graphdb.execute method and return the result as normal.

public Response alterCypher(String body, @Context GraphDatabaseService db) throws IOException, InterruptedException {

    ArrayList<Result> results = new ArrayList<>();
    // Validate our input or exit right away
    HashMap input = Validators.getValidCypherStatements(body);
    ArrayList<HashMap> statements = (ArrayList<HashMap>)input.get("statements");
    for (HashMap statement : statements) {
        // write the alterQuery method to change the queries.
        String alteredQuery = alterQuery((String)statement.get("statement"));
        Result result = db.execute(alteredQuery, (Map)statement.getOrDefault("parameters", new HashMap<>()));
    // or go the results and return them however you want 
    // see https://github.com/dmontag/neo4j-unmanaged-extension-template/blob/master/src/main/java/org/neo4j/example/unmanagedextension/MyService.java#L36
    return Response.ok().build();

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Asked in February 2016
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