Two filters in one query & nested queries

[vaishali-legislate]

Hi,

I've included both questions in one post, because both problems are related to the same set of code, so I thought it would be easier to include both in one discussion.

Two filters in a SPARQL query
I am trying to apply two filters to a SPARQL query and I'm not sure how to do so. This is the code I have at the moment:

[Block of code]

private Logger logger = LoggerFactory.getLogger(getClass());

Variable otherLetter = SparqlBuilder.var("letter");
Variable otherFieldStore = SparqlBuilder.var("otherFieldStore");
Variable fieldStore = SparqlBuilder.var("fieldStore");
Variable endDate = SparqlBuilder.var("endDate");
Variable startDate = SparqlBuilder.var("startDate");
Variable price = SparqlBuilder.var("price");
Variable otherPrice = SparqlBuilder.var("otherPrice");
Variable lessCount = SparqlBuilder.var("lessCount");
Variable equalCount = SparqlBuilder.var("equalCount");


Expression<?> nowFunc = Expressions.function(SparqlFunction.NOW );
Expression<?> endDateGreaterThan = Expressions.gt(endDate, nowFunc);
Expression<?> startDateLessThan = Expressions.lt(startDate, nowFunc);

Aggregate countOtherLetter = Expressions.count(otherLetter);
Aggregate minAgg = Expressions.min(otherPrice);

GraphPattern query3 = otherLetter.isA(lg.iri("Letter")).
       andHas(lg.iri("fieldStore"), otherFieldStore).
       and(GraphPatterns.tp(otherFieldStore, lg.iri("endDate"), endDate)).
       and(GraphPatterns.tp(otherFieldStore, lg.iri("startDate"), startDate)).
       and(GraphPatterns.tp(otherFieldStore, lg.iri("finalPrice"), otherPrice)).
       and(GraphPatterns.tp(fieldStore, lg.iri("finalPrice"), price)).
       filter(Expressions.and(endDateGreaterThan, startDateLessThan)).
       filter(Expressions.equals(otherPrice, price));

SelectQuery combinedQuery = Queries.SELECT(countOtherLetter.as(equalCount), fieldStore).
       where(query3).groupBy(fieldStore);

String query3String = query3.getQueryString();

        logger.info(query3String);
        logger.info(combinedQueryString);

which gives me the following query:

                SELECT (COUNT(?otherLetter) AS ?equalCount) ?fieldStore WHERE { \
                    ?otherLetter a :Letter . \
                    ?otherLetter :fieldStore ?otherFieldStore . \
                    ?otherFieldStore :endDate ?endDate . \
                    ?otherFieldStore :startDate ?startDate . \
                    ?otherFieldStore :finalPrice ?otherPrice . \
                    ?fieldStore :finalPrice ?price . \
                    FILTER(?otherTotalHouseRent = ?totalHouseRent) . \
                } GROUP BY ?fieldStore \

However, the query I would like is this:

                SELECT (COUNT(?otherLetter) AS ?equalCount) ?fieldStore WHERE { \
                    ?otherLetter a :Letter . \
                    ?otherLetter :fieldStore ?otherFieldStore . \
                    ?otherFieldStore :endDate ?endDate . \
                    ?otherFieldStore :startDate ?startDate . \
                    ?otherFieldStore :finalPrice ?otherPrice . \
                    ?fieldStore :finalPrice ?price . \
                    FILTER(?endDate > NOW() && ?startDate < NOW()) . \
                    FILTER(?otherPrice = ?price) . \
                } GROUP BY ?fieldStore \

How can I achieve this?

Nested queries

Related to the above queries, if I would like to create a nested query that looks something like this:

 SELECT (MIN(?otherPrice) AS ?minPrice) WHERE { \
                ?otherLetter a :Letter . \
                ?otherLetter :fieldStore ?otherFieldStore . \
                ?otherLetter :endDate ?endDate . \
                ?otherLetter :startDate ?startDate . \
                ?otherFieldStore :finalPrice ?otherPrice . \
                FILTER(?endDate > NOW() && ?startDate < NOW() ) . \
            } \
    } . \
    { \
        SELECT ?fieldStore ?lessCount ?equalCount WHERE { \
            { \
                    SELECT (COUNT(?otherLetter) AS ?equalCount) ?fieldStore WHERE { \
                    ?otherLetter a :Letter . \
                    ?otherLetter :fieldStore ?otherFieldStore . \
                    ?otherFieldStore :endDate ?endDate . \
                    ?otherFieldStore :startDate ?startDate . \
                    ?otherFieldStore :finalPrice ?otherPrice . \
                    ?fieldStore :finalPrice ?price . \
                    FILTER(?endDate > NOW() && ?startDate < NOW()) . \
                    FILTER(?otherTotalHouseRent = ?totalHouseRent) . \
                } GROUP BY ?fieldStore \

The same [Block of code] referred to above can be used for this query, I just didn't know how to get it to work. I tried something below and it didn't achieve what I wanted it to (it is incomplete and only tackles the second part of the query, not the first):

SelectQuery combinedQuery = Queries.SELECT(fieldStore, lessCount, equalCount).where().
                select(countOtherLetter.as(equalCount), fieldStore).
                where(query3).groupBy(fieldStore);

Any help would be appreciated, sorry if the questions are tedious, I'm still getting familiar with rdf4j and am a beginner in coding!

Thank you :)

[abrokenjester]

I am actually not entirely sure how you can create more than one filter clause in the same group graph pattern. It should be possible, but it looks as if the SparqlBuilder simply assumes that there will alway only one filter clause. I'm either overlooking something, or this is a bug (or at least a shortcoming).

A workaround is just to put your constraints in the single filter clause:

.filter(Expressions.and(endDateGreaterThan, startDateLessThan, Expressions.equals(otherPrice, price))));

Doesn't give you exact result you're after, but the meaning of the query is the same.

As for your second question, assuming that what you're struggling with is getting the subselect to work, have a look at this code example: https://github.com/eclipse/rdf4j/blob/main/core/sparqlbuilder/src/test/java/org/eclipse/rdf4j/sparqlbuilder/examples/sparql11spec/Section12Test.java .

As a matter of fact, the entire directory https://github.com/eclipse/rdf4j/blob/main/core/sparqlbuilder/src/test/java/org/eclipse/rdf4j/sparqlbuilder/examples/sparql11spec might be of interest to you. It shows usage example for all queries in the official SPARQL Recommendation (https://www.w3.org/TR/sparql11-query/), section by section.

[vaishali-legislate]

Thank you! That is extremely helpful. I don't see a example set for section 10 of the SPARQL docs, are there any examples for this? As I am struggling with the bind function and how to use it within rdf4j.

[abrokenjester]

Afraid not, but this is because use of the BIND expression is currently not supported in the SparqlBuilder.

[vaishali-legislate]

Thank you for your help!!