Java Code Examples for org.eclipse.rdf4j.query.algebra.evaluation.QueryBindingSet#getValue()

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Example 1
Source File: PCJKeyToCrossProductBindingSetIterator.java    From rya with Apache License 2.0 6 votes vote down vote up 
/**
 * This method compute the cross product of the BindingSet passed to the PCJ
 * and the PCJ BindingSet.  It verifies that only common variables are unassured
 * variables, and if leftBs and rightBs have distinct values for a given variable,
 * this method uses the value from leftBs in the cross product BindingSet - this
 * is effectively performing a LeftJoin.
 *
 * @param leftBs - BindingSet passed to PCJ
 * @param rightBs - PCJ BindingSet
 * @return - cross product BindingSet
 */
private BindingSet takeCrossProduct(BindingSet leftBs, BindingSet rightBs) {
	if (bindingSetsIntersect(leftBs, rightBs)) {
		return EMPTY_BINDINGSET;
	}
	QueryBindingSet bs = new QueryBindingSet(leftBs);

	//only add Bindings corresponding to variables that have no value
	//assigned.  This takes into account case where leftBs and rightBs
	//share a common, unAssuredVariable.  In this case, use value corresponding
	//to leftBs, which is effectively performing a LeftJoin.
	for(String s: rightBs.getBindingNames()) {
		if(bs.getValue(s) == null) {
			bs.addBinding(s, rightBs.getValue(s));
		}
	}
	return bs;
}
Example 2
Source File: StrictEvaluationStrategy.java    From rdf4j with BSD 3-Clause "New" or "Revised" License 4 votes vote down vote up 
public CloseableIteration<BindingSet, QueryEvaluationException> evaluate(BindingSetAssignment bsa,
		BindingSet bindings) throws QueryEvaluationException {
	final Iterator<BindingSet> iter = bsa.getBindingSets().iterator();
	if (bindings.size() == 0) { // empty binding set
		return new CloseableIteratorIteration<>(iter);
	}

	CloseableIteration<BindingSet, QueryEvaluationException> result;

	final QueryBindingSet b = new QueryBindingSet(bindings);

	result = new LookAheadIteration<BindingSet, QueryEvaluationException>() {

		@Override
		protected BindingSet getNextElement() throws QueryEvaluationException {
			QueryBindingSet result = null;
			while (result == null && iter.hasNext()) {
				final BindingSet assignedBindings = iter.next();
				for (String name : assignedBindings.getBindingNames()) {
					final Value assignedValue = assignedBindings.getValue(name);
					if (assignedValue != null) { // can be null if set to
						// UNDEF
						// check that the binding assignment does not
						// overwrite
						// existing bindings.
						Value bValue = b.getValue(name);
						if (bValue == null || assignedValue.equals(bValue)) {
							if (result == null) {
								result = new QueryBindingSet(b);
							}
							if (bValue == null) {
								// we are not overwriting an existing
								// binding.
								result.addBinding(name, assignedValue);
							}
						} else {
							// if values are not equal there is no
							// compatible
							// merge and we should return no next element.
							result = null;
							break;
						}
					}
				}
			}
			return result;
		}

	};

	return result;
}