CODEWITHSUNDEEP
neo4jcypher
FrobberOfBits
FrobberOfBits

Reputation: 18022

Is it possible to execute read only cypher queries from java?

I'd like to know just what the title says.

The reason I'd want this is to permit constrained read-only cypher queries to be executed; the data results would later be interpreted and serialized by a separate API layer.

I've seen code that makes basic assumptions in an attempt to mimic this behavior, e.g. the code might filter out any Cypher query that contains certain special words associated with write query structures (merge, create, delete, set, and so on).

This approach tends to be limited and naive though; if it very simply looks for those tokens, it would prevent a query like MATCH n WHERE n.label =~ '.*create.*' RETURN n even though it's a read-only query.

I'd really prefer not to do a full parse on a candidate query and then descend through the AST trying to figure out whether something is read-only or not (although I would gladly accept an answer that shows how to do this easily in java)

EDIT - I'm aware it's possible to start the entire database in read-only mode via the configuration property read_only=true, but this would be undesirable; no other aspect of the java API would be able to change the database.

EDIT 2 - I found another possible strategy, but I'm not sure of its advisability. Comments welcome on this, and potential downsides:

try (Transaction ignore = graphDb.beginTx()) {
    ExecutionResult result = executionEngine.execute(query);
    // Do nifty stuff with result, then...

    // Force transaction to fail.
    ignore.failure();
}

The idea here is that if queries happen within transactions and the transaction is always force-failed, then nothing can ever be written to the DB no matter what the result.

Upvotes: 0

Views: 747

Answers (1)

Stefan Armbruster
Stefan Armbruster

Reputation: 39925

Read-only Cypher is (not yet) directly supported. However I can think of two workarounds for that:

1) assuming you're running a Neo4j enterprise cluster: you can set read_only=true on one instance. That instance is then used for the read only queries where the other cluster instances are used for r/w. A load balancer in front of the cluster can be set up to send the requests to the right instance.

2) Use a TransactionEventHandler that vetos a transaction if its TransactionData contains write operations. Just for fun I've invested some minutes to implement that, see https://github.com/sarmbruster/read-only-cypher - feedback is appreciated.

Upvotes: 1

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