How do I replicate the following filter from SPARQL in java using rd4j?
FILTER(?endDate > NOW() && ?startDate < NOW() && MONTH(?endDate) = MONTH(NOW()))
I have initialised expressions for MONTH() and NOW() as follows, and a graph pattern pattern, but don't know how to use them to extract the month from variable ?endDate and from the NOW() function
Expression<?> nowFunc = Expressions.function(SparqlFunction.NOW );
Expression<?> month = Expressions.function(SparqlFunction.MONTH);
Expression<?> endDateGreaterThan = Expressions.gt(endDate, nowFunc);
Expression<?> startDateLessThan = Expressions.lt(startDate, nowFunc);
The query I have so far is as follows, but I can't figure out how to implement the final part (****) of the filter into the query.
SelectQuery query = Queries.SELECT().prefix(ex).select(letter).where(pattern.filter(Expressions.
and(endDateGreaterThan, startDateLessThan, ****)
It's no different from how you have set up your other expressions. You want an equals comparison operation between two value expressions (let's call them leftArg and rightArg), so:
Expression monthEquals = Expressions.equals(leftArg, rightArg);
Your leftArg and rightArg are both also functions, both with a single operand. The leftArg has a simple variable as its function operand:
Expression leftArg = Expressions.function(SparqlFunction.MONTH, endDate);
The rightArg has a NOW() function as its operand:
Expression rightArg = Expressions.function(SparqlFunction.MONTH,
Expressions.function(SparqlFunction.NOW));
Just put it all together and you're done.