Usages of Neo4j ResultConverter Interface

Question

I recently bumped into the ResultConverter interface in Neo4j when examining the following method on the RestAPIFacade class...

org.neo4j.rest.graphdb.RestAPIFacade.query(String statement, Map<String, Object> params, ResultConverter resultConverter)

Thinking it might be involved in the conversion of a query result to a specified java class as the code below suggests..

public interface ResultConverter<T, R> {
R convert(T value, Class<R> type);

ResultConverter NO_OP_RESULT_CONVERTER = new ResultConverter() {
    @Override
    public Object convert(Object value, Class type) {
        return null;
    }
};

}

I started digging around for documentation on usage of the interface and what the types T and R(I'm kind of suspecting that the R might be the class to convert to) but I've come up short so far. Can anyone give me a heads up on what this is supposed to do in the context of the query method? Examples would really help.

Thanks.

Answer 1

If you look at the result type of the query method in RestAPIFacade, you'll see that it returns a QueryResult<T>

on QueryResult you have a bunch of methods to convert your result to other types, and these methods then use the result-converter to do the conversion.

public interface QueryResult<T> extends Iterable<T> {
    <R> ConvertedResult<R> to(Class<R> type);
    <R> ConvertedResult<R> to(Class<R> type, ResultConverter<T, R> resultConverter);
    void handle(Handler<T> handler);
}

Where the to methods return a ConvertedResult which then is either an Iterable of type R or has methods to access a single value of type R.

public interface ConvertedResult<R> extends Iterable<R> {
    R single();
    R singleOrNull();
    void handle(Handler<R> handler);
}

So in this case T is Map<String, Object> and R would be your target type. The default Converter supports conversion to node and path objects and vice versa. See the implementation here.