Reusing Statement with different property values

[zakjan]

Hi,

Constructing Cypher DSL statements has a performance overhead which makes it unusable in cycles. SDN suffers from the same issue, promotes creating a new Cypher DSL statement for every call. https://docs.spring.io/spring-data/neo4j/docs/7.1.5/reference/html/#sdn-mixins.using-cypher-dsl-statements

(I know, database queries shouldn't be used in cycles to avoid N+1 query problem, but in my case it's caused by legacy Neo4j usage patterns which originate from the embedded mode. To be refactored separately. 😮‍💨)

For constructing Cypher DSL statement just once and reusing with different parameter values, currently a wrapper class is necessary:

record CachedStatement(String cypher, Map<String, Object> parameters) {}

Usage:

class CarStatements {

    private static String NAME_KEY = "name";

    private static GET_CARS_STATEMENT = getCarsStatement();

    private static Statement getCarsStatement() {
        Parameter<?> nameParameter = Cypher.parameter(NAME_KEY);

        Node car = Cypher.node("Car").named("car");

        return Cypher.match(car).where(car.property("name").eq(nameParameter)).returning(car).build();
    }

    public static CachedStatement getCars(String name) {
        return new CachedStatement(GET_CARS_STATEMENT.getCypher(), Map.of(NAME_KEY, name));
    }
}

Is it feasible to add a method to Statement for creating a new instance with copied already rendered Cypher string and binding new parameter values, so that Cypher is reused? Potential usage:

    public static Statement getCars(String name) {
        return GET_CARS_STATEMENT.withParameters(Map.of(NAME_KEY, name));
    }

or

    private static Parameter<?> NAME_PARAMETER = Cypher.parameter("name");

    public static Statement getCars(String name) {
        return GET_CARS_STATEMENT.withParameters(Map.of(NAME_PARAMETER, name));
    }

Depends on how to share the parameters between query construction and binding. I wonder what could be the most idiomatic way.

[michael-simons]

Interesting question.
We do cache statements, but that doesn't solve the parameter issue.

[zakjan]

Exactly. What's the cached query used for currently?

[michael-simons]

if you render the statement a second time (you get the cached string)

https://github.com/neo4j-contrib/cypher-dsl/blob/f278f67e8f0fa2d5fad2f46d0f5eaf94461d7993/neo4j-cypher-dsl/src/main/java/org/neo4j/cypherdsl/core/renderer/ConfigurableRenderer.java#L90-L96

You could just incorporate the parameters here, but to have them, you would need to visit the AST first, which kinda defeats the purpose.

Need to think about this a bit, it's at least 50% already there… If you have a good idea, happy to work on a PR.

[michael-simons]

But wait… For what you are doing, wouldn't that work already?

@Test
void withArgs() {

	var movie = Cypher.node("Movie").named("n");
	var statement = Cypher.match(movie.where(
		movie.property("title").eq(Cypher.parameter("whatever")).or(movie.property("year").gte(Cypher.anonParameter(1999))))).returning(movie).build();

	var result1 = Renderer.getDefaultRenderer().render(statement);
	assertThat(result1).isSameAs(Renderer.getDefaultRenderer().render(statement));
	assertThat(result1).isEqualTo("MATCH (n:`Movie` WHERE (n.title = $whatever OR n.year >= $pcdsl01)) RETURN n");

	try(var driver = GraphDatabase.driver("neo4j://localhost", AuthTokens.none())) {
		for(String value : List.of("value1", "value2")) {
			// Get all the anonymous parameters and their values
			var parameters = new HashMap<>(statement.getCatalog().getParameters());
			// add all named
			parameters.put("whatever", value);
			// parameters are now {whatever=value1, pcdsl01=1999}
			driver.executableQuery(result1)
				.withParameters(parameters)
				.execute();
		}
	}
}

You just actually need to use the parameters for your properties :)

[zakjan]

When it's inlined like this, yes. But consider that the part creating and running the DSL query is in a separate repository. Either a custom repository implementation or SDN.

for(String value : List.of("value1", "value2")) {
    movieRepository.getMovie(value);
}