/// <summary>
/// Executes a Graph Pattern style query against the Source
/// </summary>
/// <param name="graph">Graph Pattern</param>
/// <param name="options">Query Options</param>
/// <param name="sink">Results Sink</param>
/// <remarks>
/// <para>
/// This is implemented by transforming the Graph Pattern which is a set of SemWeb Statement templates into a SPARQL Algebra BGP. The resulting algebra is then executed using the Leviathan engine and the results converted into VariableBindings for SemWeb
/// </para>
/// <para>
/// The only Query Option that is supported is the Limit option
/// </para>
/// </remarks>
public void Query(Statement[] graph, SW.Query.QueryOptions options, SW.Query.QueryResultSink sink)
{
ISparqlAlgebra algebra = this.ToAlgebra(graph);
SparqlEvaluationContext context = new SparqlEvaluationContext(null, new InMemoryDataset(this._store));
BaseMultiset results = context.Evaluate(algebra);//algebra.Evaluate(context);
sink.Init(results.Variables.Select(v => new Variable(v)).ToArray());
if (results.Count > 0)
{
int c = 0;
foreach (Set s in results.Sets)
{
//Apply Limit if applicable
if (options.Limit > 0 && c >= options.Limit)
{
sink.Finished();
return;
}
//Convert the Set to VariableBindings for SemWeb
Variable[] vars = s.Variables.Select(v => new Variable(v)).ToArray();
Resource[] resources = s.Variables.Select(v => SemWebConverter.ToSemWeb(s[v], this.GetMapping(s[v].Graph))).ToArray();
SW.Query.VariableBindings bindings = new SW.Query.VariableBindings(vars, resources);
//Keep adding results until the sink tells us to stop
if (!sink.Add(bindings))
{
sink.Finished();
return;
}
c++;
}
sink.Finished();
}
else
{
sink.Finished();
}
}
/// <summary>
/// Evaluates the Command in the given Context
/// </summary>
/// <param name="context">Evaluation Context</param>
public override void Evaluate(SparqlUpdateEvaluationContext context)
{
bool defGraphOk = false;
bool datasetOk = false;
try
{
//First evaluate the WHERE pattern to get the affected bindings
ISparqlAlgebra where = this._wherePattern.ToAlgebra();
if (context.Commands != null)
{
where = context.Commands.ApplyAlgebraOptimisers(where);
}
//Set Active Graph for the WHERE based upon the WITH clause
//Don't bother if there are USING URIs as these would override any Active Graph we set here
//so we can save ourselves the effort of doing this
if (!this.UsingUris.Any())
{
if (this._graphUri != null)
{
context.Data.SetActiveGraph(this._graphUri);
defGraphOk = true;
}
else
{
context.Data.SetActiveGraph((Uri)null);
defGraphOk = true;
}
}
//We need to make a dummy SparqlQuery object since if the Command has used any
//USING/USING NAMEDs along with GRAPH clauses then the algebra needs to have the
//URIs available to it which it gets from the Query property of the Context
//object
SparqlQuery query = new SparqlQuery();
foreach (Uri u in this.UsingUris)
{
query.AddDefaultGraph(u);
}
foreach (Uri u in this.UsingNamedUris)
{
query.AddNamedGraph(u);
}
SparqlEvaluationContext queryContext = new SparqlEvaluationContext(query, context.Data, context.QueryProcessor);
if (this.UsingUris.Any())
{
//If there are USING URIs set the Active Graph to be formed of the Graphs with those URIs
context.Data.SetActiveGraph(this._usingUris);
datasetOk = true;
}
BaseMultiset results = queryContext.Evaluate(where);
if (this.UsingUris.Any())
{
//If there are USING URIs reset the Active Graph afterwards
//Also flag the dataset as no longer being OK as this flag is used in the finally
//block to determine whether the Active Graph needs resetting which it may do if the
//evaluation of the
context.Data.ResetActiveGraph();
datasetOk = false;
}
//Reset Active Graph for the WHERE
if (defGraphOk)
{
context.Data.ResetActiveGraph();
defGraphOk = false;
}
//Get the Graph from which we are deleting
IGraph g = context.Data.GetModifiableGraph(this._graphUri);
//Delete the Triples for each Solution
foreach (ISet s in queryContext.OutputMultiset.Sets)
{
List<Triple> deletedTriples = new List<Triple>();
//Triples from raw Triple Patterns
try
{
ConstructContext constructContext = new ConstructContext(g, s, true);
foreach (IConstructTriplePattern p in this._deletePattern.TriplePatterns.OfType<IConstructTriplePattern>())
{
try
{
deletedTriples.Add(p.Construct(constructContext));
}
catch (RdfQueryException)
{
//If we get an error here then we couldn't construct a specific Triple
//so we continue anyway
}
}
g.Retract(deletedTriples);
}
catch (RdfQueryException)
{
//If we throw an error this means we couldn't construct for this solution so the
//solution is ignored this graph
}
//Triples from GRAPH clauses
foreach (GraphPattern gp in this._deletePattern.ChildGraphPatterns)
{
deletedTriples.Clear();
try
{
String graphUri;
switch (gp.GraphSpecifier.TokenType)
{
case Token.URI:
graphUri = gp.GraphSpecifier.Value;
break;
case Token.VARIABLE:
if (s.ContainsVariable(gp.GraphSpecifier.Value))
{
INode temp = s[gp.GraphSpecifier.Value.Substring(1)];
if (temp == null)
{
//If the Variable is not bound then skip
continue;
}
else if (temp.NodeType == NodeType.Uri)
{
graphUri = temp.ToSafeString();
}
else
{
//If the Variable is not bound to a URI then skip
continue;
}
}
else
{
//If the Variable is not bound for this solution then skip
continue;
}
break;
default:
//Any other Graph Specifier we have to ignore this solution
continue;
}
//If the Dataset doesn't contain the Graph then no need to do the Deletions
if (!context.Data.HasGraph(UriFactory.Create(graphUri))) continue;
//Do the actual Deletions
IGraph h = context.Data.GetModifiableGraph(UriFactory.Create(graphUri));
ConstructContext constructContext = new ConstructContext(h, s, true);
foreach (IConstructTriplePattern p in gp.TriplePatterns.OfType<IConstructTriplePattern>())
{
try
{
deletedTriples.Add(p.Construct(constructContext));
}
catch (RdfQueryException)
{
//If we get an error here then we couldn't construct a specific
//triple so we continue anyway
}
}
h.Retract(deletedTriples);
}
catch (RdfQueryException)
{
//If we get an error here this means we couldn't construct for this solution so the
//solution is ignored for this graph
}
}
}
}
finally
{
//If the Dataset was set and an error occurred in doing the WHERE clause then
//we'll need to Reset the Active Graph
if (datasetOk) context.Data.ResetActiveGraph();
if (defGraphOk) context.Data.ResetActiveGraph();
}
}
