Examples with EmptyIteration org.eclipse.rdf4j.common.iteration.EmptyIteration used on opensource projects

Example 1 with EmptyIteration

use of org.eclipse.rdf4j.common.iteration.EmptyIteration in project rdf4j by eclipse.

the class RepositoryFederatedService method evaluateInternal.

/**
 * Evaluate the SPARQL query that can be constructed from the SERVICE node at the initialized
 * {@link Repository} of this {@link FederatedService}. Use specified bindings as constraints to the
 * query. Try to evaluate using BINDINGS clause, if this yields an exception fall back to the naive
 * implementation. This method deals with SILENT SERVICEs.
 */
protected CloseableIteration<BindingSet, QueryEvaluationException> evaluateInternal(Service service, CloseableIteration<BindingSet, QueryEvaluationException> bindings, String baseUri) throws QueryEvaluationException {
    // materialize all bindings (to allow for fallback in case of errors)
    // note that this may be blocking depending on the underlying iterator
    List<BindingSet> allBindings = new LinkedList<BindingSet>();
    while (bindings.hasNext()) {
        allBindings.add(bindings.next());
    }
    if (allBindings.size() == 0) {
        return new EmptyIteration<BindingSet, QueryEvaluationException>();
    }
    // projection vars
    Set<String> projectionVars = new HashSet<String>(service.getServiceVars());
    projectionVars.removeAll(allBindings.get(0).getBindingNames());
    // below we need to take care for SILENT services
    CloseableIteration<BindingSet, QueryEvaluationException> result = null;
    try {
        // fallback to simple evaluation (just a single binding)
        if (allBindings.size() == 1) {
            result = select(service, projectionVars, allBindings.get(0), baseUri);
            result = service.isSilent() ? new SilentIteration(result) : result;
            return result;
        }
        // To be able to insert the input bindings again later on, we need some
        // means to identify the row of each binding. hence, we use an
        // additional
        // projection variable, which is also passed in the BINDINGS clause
        // with the value of the actual row. The value corresponds to the index
        // of the binding in the index list
        projectionVars.add("__rowIdx");
        String queryString = service.getSelectQueryString(projectionVars);
        List<String> relevantBindingNames = getRelevantBindingNames(allBindings, service.getServiceVars());
        if (relevantBindingNames.size() != 0) {
            // append the VALUES clause to the query
            queryString += buildVALUESClause(allBindings, relevantBindingNames);
        }
        TupleQuery query = getConnection().prepareTupleQuery(QueryLanguage.SPARQL, queryString, baseUri);
        TupleQueryResult res = null;
        // TODO how to retrieve max query value
        query.setMaxQueryTime(60);
        // from actual setting?
        res = query.evaluate();
        if (relevantBindingNames.size() == 0)
            // cross
            result = new SPARQLCrossProductIteration(res, allBindings);
        else
            // product
            // common
            result = new ServiceJoinConversionIteration(res, allBindings);
        // join
        result = service.isSilent() ? new SilentIteration(result) : result;
        return result;
    } catch (RepositoryException e) {
        Iterations.closeCloseable(result);
        if (service.isSilent())
            return new CollectionIteration<BindingSet, QueryEvaluationException>(allBindings);
        throw new QueryEvaluationException("Repository for endpoint " + rep.toString() + " could not be initialized.", e);
    } catch (MalformedQueryException e) {
        // this exception must not be silenced, bug in our code
        throw new QueryEvaluationException(e);
    } catch (QueryEvaluationException e) {
        Iterations.closeCloseable(result);
        if (service.isSilent())
            return new CollectionIteration<BindingSet, QueryEvaluationException>(allBindings);
        throw e;
    } catch (RuntimeException e) {
        Iterations.closeCloseable(result);
        // QueryEval) if silent
        if (service.isSilent())
            return new CollectionIteration<BindingSet, QueryEvaluationException>(allBindings);
        throw e;
    }
}