Is it possible to retrieve relationship types from collection?

[DonCziken]

Hi Wolfgang,

say I'd like to do following:

        JcPath p;
        [..]
        WHERE.valueOf(p.relations().head().type()).EQUALS("someType")

but the problem is that p.relations().head() returns ValueElementwhich I can't find a way to convert to Relation using available API. Another example of such a case maybe following:

MATCH.node(n0).label("JcTestPerson")
                .relation(r0).out().minHops(0)
                .node(n1),
            RETURN.value(n0.name)
            RETURN.value((r[i - 1].asCollection().head().type()).as(new JcString("type"))
            RETURN.value(n1.name)

so Question to you Wolfgang - is it possible to retrieve type from relation picked from JcCollection? If so how can I do that? Just FYI in mean time I had prepared a workaround for above doing following, but its very dirty :)

public class JcStringExtension {

    public static JcString create(Object val, ValueElement predecessor, IOperatorOrFunction opf) {
        try {
            Constructor<?> constructor  = JcString.class.getDeclaredConstructor(Object.class,
                ValueElement.class, IOperatorOrFunction.class);
            constructor.setAccessible(true);
            return (JcString) constructor.newInstance(val, predecessor, opf);
        } catch (NoSuchMethodException | InstantiationException
            | IllegalAccessException | InvocationTargetException e) {
            EigenLog.errorLog(e.getMessage());
            throw new DomainApiException("Internal error - please check logs");
        }
    }

}

public class FunctionInstanceExtension {

    public static FunctionInstance create(Function function, int numArgs) {

        try {
            Constructor<?> constructor = FunctionInstance.class
                .getDeclaredConstructor(Function.class,
                    int.class);
            constructor.setAccessible(true);
            return (FunctionInstance) constructor.newInstance(function, numArgs);
        } catch (NoSuchMethodException | InstantiationException
            | IllegalAccessException | InvocationTargetException e) {
            EigenLog.errorLog(e.getMessage());
            throw new DomainApiException("Internal error - please check logs");
        }
    }

}

//usage:
    @SuppressWarnings("unchecked")
    private JcString typeOfValueElement(ValueElement v) {
        return JcStringExtension.create(null, v,
            FunctionInstanceExtension.create(FUNCTION.Relation.TYPE, 1));
    }

RETURN.value(typeOfValueElement((r[i - 1].asCollection().head())))
                .AS(r[i - 1])

cheers, Krzysztof

[Wolfgang-Schuetzelhofer]

Hi Krzysztov,

I see your problem. Could you send me a CYPHER expression that would do the job? Then I will try to find a solution.

Best regards, Wolfgang ,

On Tue, Sep 4, 2018 at 1:34 AM Krzysztof Gasior notifications@github.com wrote:

say I'd like to do following:

    JcPath p;
    [..]
    WHERE.valueOf(p.relations().head().type()).EQUALS("someType")

but the problem is that p.relations().head() returns ValueElementwhich I can't find a way to convert to Relation using available API. Another example of usch a case maybe following:

MATCH.node(n0).label("JcTestPerson") .relation(r0).out().minHops(0) .node(n1), RETURN.value(n0.name) RETURN.value((r[i - 1].asCollection().head().type()).as(new JcString("type")) RETURN.value(n1.name)

so Question to you Wolfgang - is it possible to retrieve type from relation picked from JcCollection? If so how can I do that? Just FYI in mean time I had prepared a workaround for above doing following, but its very dirty :)

public class JcStringExtension {

public static JcString create(Object val, ValueElement predecessor, IOperatorOrFunction opf) {
    try {
        Constructor<?> constructor  = JcString.class.getDeclaredConstructor(Object.class,
            ValueElement.class, IOperatorOrFunction.class);
        constructor.setAccessible(true);
        return (JcString) constructor.newInstance(val, predecessor, opf);
    } catch (NoSuchMethodException | InstantiationException
        | IllegalAccessException | InvocationTargetException e) {
        EigenLog.errorLog(e.getMessage());
        throw new DomainApiException("Internal error - please check logs");
    }
}

}

public class FunctionInstanceExtension {

public static FunctionInstance create(Function function, int numArgs) {

    try {
        Constructor<?> constructor = FunctionInstance.class
            .getDeclaredConstructor(Function.class,
                int.class);
        constructor.setAccessible(true);
        return (FunctionInstance) constructor.newInstance(function, numArgs);
    } catch (NoSuchMethodException | InstantiationException
        | IllegalAccessException | InvocationTargetException e) {
        EigenLog.errorLog(e.getMessage());
        throw new DomainApiException("Internal error - please check logs");
    }
}

}

//usage: @SuppressWarnings("unchecked") private JcString typeOfValueElement(ValueElement v) { return JcStringExtension.create(null, v, FunctionInstanceExtension.create(FUNCTION.Relation.TYPE, 1)); }

RETURN.value(typeOfValueElement((r[i - 1].asCollection().head()))) .AS(r[i - 1])

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[DonCziken]

Hi Wolfgang,

i.e.

MATCH (n0)-[r0*0..1]->(n1)-[r1*0..1]->(n2) 
WHERE id(n0)=560725 
RETURN DISTINCT id(n0), n0.name, type(r0[0]), id(n1), n1.name, type(r1[0]), id(n2), n2.name

note: type(r0[0]) and type(r1[0]) in RETURN statement

[Wolfgang-Schuetzelhofer]

Hi Krzysztov,

the quick solution: For cypher statements which are not or not yet supported in JCypher, you can always use JCypher's NATIVE clause. By means of the NATIVE clause you can write parts of a query or even an entire query in cypher. For your example please see below:

clauses = new IClause[]{
  MATCH.node(n0).relation(r0).minHops(0).maxHops(1).out()
    .node(n1).relation(r1).minHops(0).maxHops(1).out().node(n2),
  WHERE.valueOf(n0.id()).EQUALS(560725),
  NATIVE.cypher("RETURN DISTINCT id(n0), n0.name, type(r0[0]), id(n1), n1.name, type(r1[0]), id(n2), n2.name")
};

This leads to the cypher query:

MATCH (n0)-[r0*0..1]->(n1)-[r1*0..1]->(n2)
WHERE id(n0) = 560725
RETURN DISTINCT id(n0), n0.name, type(r0[0]), id(n1), n1.name, type(r1[0]), id(n2), n2.name

I will extend JCypher' API to support your scenario with the next release. Sorry if I take some time to answer your mails, that is because I am currently engaged in a customer project which takes almost all of my time. So currently I don't have much time to work on JCypher.

Best regards, Wolfgang

[DonCziken]

Hi Wolfgang,

thanks for reply, its good to know that it is possible to combine Query DSL with NATIVE.cypher this would help in such cases :).

Let me know when you got a fix for that within DSL, and for the moment I i will stick with my dirty hack using JcStringExtension and FunctionInstanceExtension.

cheers, Krzysztof

[Wolfgang-Schuetzelhofer]

Hi Krzysztov, JCypher 4.1.0 is released, now collections in the Query API are aware of their component type. You should now be able to do what you were looking for:

    JcPath p;
    [..]
    WHERE.valueOf(p.relations().head().type()).EQUALS("someType")

cheers, Wolfgang

[DonCziken]

Hi Wolfgang,

much appreciate!

cheers, Krzysztof