Java Code Examples for org.eclipse.rdf4j.query.algebra.ProjectionElemList#addElement()

/**
 * Construct a SELECT query for a grouped bound check.
 * 
 * Pattern:
 * 
 * SELECT DISTINCT ?o_1 .. ?o_N WHERE { { s1 p1 ?o_1 FILTER ?o_1=o1 } UNION ... UNION { sN pN ?o_N FILTER ?o_N=oN }}
 * 
 * @param stmt
 * @param unionBindings
 * @return
 */
public static TupleExpr selectQueryStringBoundCheck(StatementPattern stmt, List<BindingSet> unionBindings) {
	
	Set<String> varNames = new HashSet<String>();
	
	Union union = new Union();
	union.setLeftArg(constructStatementCheckId(stmt, 0, varNames, unionBindings.get(0)) );
	Union tmp = union;
	int idx;
	for (idx=1; idx<unionBindings.size()-1; idx++) {
		Union _u = new Union();
		_u.setLeftArg( constructStatementCheckId(stmt, idx, varNames, unionBindings.get(idx)) );
		tmp.setRightArg(_u);
		tmp = _u;
	}
	tmp.setRightArg( constructStatementCheckId(stmt, idx, varNames, unionBindings.get(idx) ));
	
	ProjectionElemList projList = new ProjectionElemList();
	for (String var : varNames)
		projList.addElement( new ProjectionElem(var));
	
	Projection proj = new Projection(union, projList);

	return proj;
}
 

/**
 * Construct a SELECT query for a grouped bound check.
 *
 * Pattern:
 *
 * SELECT DISTINCT ?o_1 .. ?o_N WHERE { { s1 p1 ?o_1 FILTER ?o_1=o1 } UNION ... UNION { sN pN ?o_N FILTER ?o_N=oN }}
 *
 * @param stmt
 * @param unionBindings
 * @return the SELECT query
 */
public static TupleExpr selectQueryStringBoundCheck(StatementPattern stmt, List<BindingSet> unionBindings) {

	Set<String> varNames = new HashSet<>();

	Union union = new Union();
	union.setLeftArg(constructStatementCheckId(stmt, 0, varNames, unionBindings.get(0)));
	Union tmp = union;
	int idx;
	for (idx = 1; idx < unionBindings.size() - 1; idx++) {
		Union _u = new Union();
		_u.setLeftArg(constructStatementCheckId(stmt, idx, varNames, unionBindings.get(idx)));
		tmp.setRightArg(_u);
		tmp = _u;
	}
	tmp.setRightArg(constructStatementCheckId(stmt, idx, varNames, unionBindings.get(idx)));

	ProjectionElemList projList = new ProjectionElemList();
	for (String var : varNames) {
		projList.addElement(new ProjectionElem(var));
	}

	Projection proj = new Projection(union, projList);

	return proj;
}
 

private Projection visitResultNodes(Resource resultNodes) throws RDF4JException {
	ProjectionElemList projElemList = new ProjectionElemList();
	Iteration<Resource, QueryEvaluationException> iter = TripleSources.listResources(resultNodes,
			store);
	while (iter.hasNext()) {
		Resource r = iter.next();
		ProjectionElem projElem = visitResultNode(r);
		projElemList.addElement(projElem);
	}

	Projection proj = new Projection();
	proj.setProjectionElemList(projElemList);

	tupleRoot = new DescribeOperator(proj);
	return proj;
}
 

private Projection visitResultVariables(Resource resultVars, Map<String, ProjectionElem> previousProjElems)
		throws RDF4JException {
	ProjectionElemList projElemList = new ProjectionElemList();
	Iteration<Resource, QueryEvaluationException> iter = TripleSources.listResources(resultVars,
			store);
	while (iter.hasNext()) {
		Resource r = iter.next();
		ProjectionElem projElem = visitResultVariable(r, previousProjElems);
		projElemList.addElement(projElem);
	}

	Projection proj = new Projection();
	proj.setProjectionElemList(projElemList);

	tupleRoot = proj;
	return proj;
}
 

private UnaryTupleOperator projection() {
	if (!mProjectionPatterns.isEmpty()) {
		return multiProjection();
	} else {
		Extension aExt = null;

		ProjectionElemList aList = new ProjectionElemList();

		for (String aVar : mProjectionVars) {
			aList.addElement(new ProjectionElem(aVar));
		}

		Projection aProjection = new Projection();
		aProjection.setProjectionElemList(aList);

		if (aExt != null) {
			aProjection.setArg(aExt);
		}

		return aProjection;
	}
}
 

/**
 * Construct a SELECT query expression for a bound union.
 * 
 * Pattern:
 * 
 * SELECT ?v_1 ?v_2 ?v_N WHERE { { ?v_1 p o } UNION { ?v_2 p o } UNION ... } 
 * 
 * Note that the filterExpr is not evaluated at the moment.
 * 
 * @param stmt
 * @param unionBindings
 * @param filterExpr
 * @param evaluated
 * 			parameter can be used outside this method to check whether FILTER has been evaluated, false in beginning
 * 
 * @return
 */
public static TupleExpr selectQueryBoundUnion( StatementPattern stmt, List<BindingSet> unionBindings, FilterValueExpr filterExpr, Boolean evaluated) {
	
	// TODO add FILTER expressions
	
	Set<String> varNames = new HashSet<String>();
	
	Union union = new Union();
	union.setLeftArg(constructStatementId(stmt, Integer.toString(0), varNames, unionBindings.get(0)) );
	Union tmp = union;
	int idx;
	for (idx=1; idx<unionBindings.size()-1; idx++) {
		Union _u = new Union();
		_u.setLeftArg( constructStatementId(stmt, Integer.toString(idx), varNames, unionBindings.get(idx)) );
		tmp.setRightArg(_u);
		tmp = _u;
	}
	tmp.setRightArg( constructStatementId(stmt, Integer.toString(idx), varNames, unionBindings.get(idx) ));
			
	ProjectionElemList projList = new ProjectionElemList();
	for (String var : varNames)
		projList.addElement( new ProjectionElem(var));
	
	Projection proj = new Projection(union, projList);

	return proj;
}
 

/**
 * Construct a SELECT query expression for a bound union.
 *
 * Pattern:
 *
 * SELECT ?v_1 ?v_2 ?v_N WHERE { { ?v_1 p o } UNION { ?v_2 p o } UNION ... }
 *
 * Note that the filterExpr is not evaluated at the moment.
 *
 * @param stmt
 * @param unionBindings
 * @param filterExpr
 * @param evaluated     parameter can be used outside this method to check whether FILTER has been evaluated, false
 *                      in beginning
 *
 * @return the SELECT query
 */
public static TupleExpr selectQueryBoundUnion(StatementPattern stmt, List<BindingSet> unionBindings,
		FilterValueExpr filterExpr, Boolean evaluated) {

	// TODO add FILTER expressions

	Set<String> varNames = new HashSet<>();

	Union union = new Union();
	union.setLeftArg(constructStatementId(stmt, Integer.toString(0), varNames, unionBindings.get(0)));
	Union tmp = union;
	int idx;
	for (idx = 1; idx < unionBindings.size() - 1; idx++) {
		Union _u = new Union();
		_u.setLeftArg(constructStatementId(stmt, Integer.toString(idx), varNames, unionBindings.get(idx)));
		tmp.setRightArg(_u);
		tmp = _u;
	}
	tmp.setRightArg(constructStatementId(stmt, Integer.toString(idx), varNames, unionBindings.get(idx)));

	ProjectionElemList projList = new ProjectionElemList();
	for (String var : varNames) {
		projList.addElement(new ProjectionElem(var));
	}

	Projection proj = new Projection(union, projList);

	return proj;
}
 

private ProjectionElemList visitTemplate(Resource r) throws RDF4JException {
	ProjectionElemList projElems = new ProjectionElemList();
	Value subj = TripleSources.singleValue(r, SP.SUBJECT_PROPERTY, store);
	projElems.addElement(createProjectionElem(subj, "subject", null));
	Value pred = TripleSources.singleValue(r, SP.PREDICATE_PROPERTY, store);
	projElems.addElement(createProjectionElem(pred, "predicate", null));
	Value obj = TripleSources.singleValue(r, SP.OBJECT_PROPERTY, store);
	projElems.addElement(createProjectionElem(obj, "object", null));
	return projElems;
}
 

private boolean addBindingNames(StringBuilder builder, boolean alreadyMapping, Map<String, String> bindings,
		ProjectionElemList list, String name) {
	boolean mapping = alreadyMapping;
	if (variables.containsKey(name)) {
		String var = variables.get(name);
		builder.append(" ?").append(var);
		bindings.put(name, var);
		list.addElement(new ProjectionElem(var, name));
		if (!name.equals(var)) {
			mapping = true;
		}
	}
	return mapping;
}
 

@Test
public void testProject() {
    final AggregationPipelineQueryNode base = new AggregationPipelineQueryNode(
            collection,
            new LinkedList<>(),
            Sets.newHashSet("x", "y"),
            Sets.newHashSet("x", "y", "opt"),
            HashBiMap.create());
    // Add a single projection
    ProjectionElemList singleProjection = new ProjectionElemList();
    singleProjection.addElement(new ProjectionElem("x", "z"));
    singleProjection.addElement(new ProjectionElem("y", "y"));
    List<ProjectionElemList> projections = Arrays.asList(singleProjection);
    AggregationPipelineQueryNode node = base.clone();
    boolean success = node.project(projections);
    Assert.assertTrue(success);
    Assert.assertEquals(1, node.getPipeline().size());
    Assert.assertEquals(Sets.newHashSet("z", "y"),
            node.getAssuredBindingNames());
    Assert.assertEquals(Sets.newHashSet("z", "y"),
            node.getBindingNames());
    // Add a multi-projection
    ProjectionElemList p1 = new ProjectionElemList();
    p1.addElement(new ProjectionElem("x", "solution"));
    ProjectionElemList p2 = new ProjectionElemList();
    p2.addElement(new ProjectionElem("y", "solution"));
    ProjectionElemList p3 = new ProjectionElemList();
    p3.addElement(new ProjectionElem("x", "x"));
    p3.addElement(new ProjectionElem("x", "solution"));
    p3.addElement(new ProjectionElem("y", "y"));
    projections = Arrays.asList(p1, p2, p3);
    node = base.clone();
    success = node.project(projections);
    Assert.assertTrue(success);
    Assert.assertEquals(3, node.getPipeline().size());
    Assert.assertEquals(Sets.newHashSet("solution"),
            node.getAssuredBindingNames());
    Assert.assertEquals(Sets.newHashSet("x", "y", "solution"),
            node.getBindingNames());
    // Add no projections
    node = base.clone();
    success = node.project(Arrays.asList());
    Assert.assertFalse(success);
    Assert.assertEquals(base, node);
}