/// <summary>
/// Sets the Default Graph for the dataset.
/// </summary>
/// <param name="graphUri">Graph URI.</param>
public virtual void SetDefaultGraph(Uri graphUri)
{
_dataset.SetDefaultGraph(graphUri);
}
/// <summary>
/// Processes a SPARQL Query sending the results to a RDF/SPARQL Results handler as appropriate.
/// </summary>
/// <param name="rdfHandler">RDF Handler.</param>
/// <param name="resultsHandler">Results Handler.</param>
/// <param name="query">SPARQL Query.</param>
public void ProcessQuery(IRdfHandler rdfHandler, ISparqlResultsHandler resultsHandler, SparqlQuery query)
{
// Do Handler null checks before evaluating the query
if (query == null)
{
throw new ArgumentNullException("query", "Cannot evaluate a null query");
}
if (rdfHandler == null && (query.QueryType == SparqlQueryType.Construct || query.QueryType == SparqlQueryType.Describe || query.QueryType == SparqlQueryType.DescribeAll))
{
throw new ArgumentNullException("rdfHandler", "Cannot use a null RDF Handler when the Query is a CONSTRUCT/DESCRIBE");
}
if (resultsHandler == null && (query.QueryType == SparqlQueryType.Ask || SparqlSpecsHelper.IsSelectQuery(query.QueryType)))
{
throw new ArgumentNullException("resultsHandler", "Cannot use a null resultsHandler when the Query is an ASK/SELECT");
}
// Handle the Thread Safety of the Query Evaluation
ReaderWriterLockSlim currLock = (_dataset is IThreadSafeDataset) ? ((IThreadSafeDataset)_dataset).Lock : _lock;
try
{
currLock.EnterReadLock();
// Reset Query Timers
query.QueryExecutionTime = null;
bool datasetOk = false, defGraphOk = false;
try
{
// Set up the Default and Active Graphs
if (query.DefaultGraphs.Any())
{
// Call HasGraph() on each Default Graph but ignore the results, we just do this
// in case a dataset has any kind of load on demand behaviour
foreach (Uri defGraphUri in query.DefaultGraphs)
{
_dataset.HasGraph(defGraphUri);
}
_dataset.SetDefaultGraph(query.DefaultGraphs);
defGraphOk = true;
}
else if (query.NamedGraphs.Any())
{
// No FROM Clauses but one/more FROM NAMED means the Default Graph is the empty graph
_dataset.SetDefaultGraph(Enumerable.Empty <Uri>());
}
_dataset.SetActiveGraph(_dataset.DefaultGraphUris);
datasetOk = true;
// Convert to Algebra and execute the Query
SparqlEvaluationContext context = GetContext(query);
BaseMultiset result;
try
{
context.StartExecution();
ISparqlAlgebra algebra = query.ToAlgebra();
result = context.Evaluate(algebra);
context.EndExecution();
query.QueryExecutionTime = new TimeSpan(context.QueryTimeTicks);
}
catch (RdfQueryException)
{
context.EndExecution();
query.QueryExecutionTime = new TimeSpan(context.QueryTimeTicks);
throw;
}
catch
{
context.EndExecution();
query.QueryExecutionTime = new TimeSpan(context.QueryTimeTicks);
throw;
}
// Return the Results
switch (query.QueryType)
{
case SparqlQueryType.Ask:
case SparqlQueryType.Select:
case SparqlQueryType.SelectAll:
case SparqlQueryType.SelectAllDistinct:
case SparqlQueryType.SelectAllReduced:
case SparqlQueryType.SelectDistinct:
case SparqlQueryType.SelectReduced:
// For SELECT and ASK can populate a Result Set directly from the Evaluation Context
// return new SparqlResultSet(context);
resultsHandler.Apply(context);
break;
case SparqlQueryType.Construct:
// Create a new Empty Graph for the Results
try
{
rdfHandler.StartRdf();
foreach (String prefix in query.NamespaceMap.Prefixes)
{
if (!rdfHandler.HandleNamespace(prefix, query.NamespaceMap.GetNamespaceUri(prefix)))
{
ParserHelper.Stop();
}
}
// Construct the Triples for each Solution
if (context.OutputMultiset is IdentityMultiset)
{
context.OutputMultiset = new SingletonMultiset();
}
foreach (ISet s in context.OutputMultiset.Sets)
{
// List<Triple> constructedTriples = new List<Triple>();
try
{
ConstructContext constructContext = new ConstructContext(rdfHandler, s, false);
foreach (IConstructTriplePattern p in query.ConstructTemplate.TriplePatterns.OfType <IConstructTriplePattern>())
{
try
{
if (!rdfHandler.HandleTriple(p.Construct(constructContext)))
{
ParserHelper.Stop();
}
// constructedTriples.Add(((IConstructTriplePattern)p).Construct(constructContext));
}
catch (RdfQueryException)
{
// If we get an error here then we could not construct a specific triple
// so we continue anyway
}
}
}
catch (RdfQueryException)
{
// If we get an error here this means we couldn't construct for this solution so the
// entire solution is discarded
continue;
}
// h.Assert(constructedTriples);
}
rdfHandler.EndRdf(true);
}
catch (RdfParsingTerminatedException)
{
rdfHandler.EndRdf(true);
}
catch
{
rdfHandler.EndRdf(false);
throw;
}
break;
case SparqlQueryType.Describe:
case SparqlQueryType.DescribeAll:
// For DESCRIBE we retrieve the Describe algorithm and apply it
ISparqlDescribe describer = query.Describer;
describer.Describe(rdfHandler, context);
break;
default:
throw new RdfQueryException("Unknown query types cannot be processed by Leviathan");
}
}
finally
{
if (defGraphOk)
{
_dataset.ResetDefaultGraph();
}
if (datasetOk)
{
_dataset.ResetActiveGraph();
}
}
}
finally
{
currLock.ExitReadLock();
}
}
