protected override String RunTaskInternal()
{
// Start from an initial Original Query issued by user
SparqlQuery initialQuery;
try
{
initialQuery = this._parser.ParseFromString(this.OriginalQueryString);
}
catch (RdfParseException parseEx)
{
throw new RdfQueryException("Unable to parse the given SPARQL Query", parseEx);
}
if (initialQuery.QueryType != SparqlQueryType.Select && initialQuery.QueryType != SparqlQueryType.SelectDistinct)
{
throw new RdfQueryException("Only Sparql select Query with variables is supported for table format");
}
INamespaceMapper originalPrefixes = new NamespaceMapper(true);
originalPrefixes.Import(initialQuery.NamespaceMap);
initialQuery.NamespaceMap.Clear();
// Get the predicates for first variable (entity subjects)
// SELECT DISTINCT ?p (COUNT(?p) as ?count)
// WHERE
// {
// {
// # Original Query
// }
// ?sx ?p ?o.
// }
// GROUP BY ?p
// Create a dynamic originalQuery
SparqlVariable subject = initialQuery.Variables.FirstOrDefault(v => v.IsResultVariable);
if (subject == null)
{
throw new RdfQueryException("At least one result variable is required to generate an entities query");
}
INode subjectNode = this._nodeFactory.CreateVariableNode(subject.Name);
SparqlParameterizedString getPredicatesQuery = new SparqlParameterizedString();
getPredicatesQuery.Namespaces = originalPrefixes;
getPredicatesQuery.CommandText = @"
SELECT DISTINCT ?p (COUNT(?p) as ?count)
WHERE
{";
getPredicatesQuery.AppendSubQuery(initialQuery);
getPredicatesQuery.CommandText += @"
@subject ?p ?o.
}
GROUP BY ?p";
getPredicatesQuery.SetParameter("subject", subjectNode);
try
{
// Get predicates and number of usages
this.Information = "Running query to extract predicates for entities selected by original query...";
SparqlResultSet sparqlResults = (SparqlResultSet)this._storage.Query(getPredicatesQuery.ToString());
if (sparqlResults == null)
{
throw new RdfQueryException("Unexpected results type received while trying to build entities query");
}
List <String> selectColumns = new List <String>();
selectColumns.Add(subject.Name);
SparqlParameterizedString entitiesQuery = new SparqlParameterizedString();
entitiesQuery.Namespaces.Import(getPredicatesQuery.Namespaces);
entitiesQuery.SetParameter("subject", subjectNode);
// For each predicate add a column and an appropriate OPTIONAL clause
int predicateIndex = 0;
StringBuilder optionalFilters = new StringBuilder();
this.Information = "Generating Entities Query...";
foreach (SparqlResult sparqlResult in sparqlResults)
{
if (!sparqlResult.HasBoundValue("p"))
{
continue;
}
INode predicate = sparqlResult["p"];
IValuedNode count = sparqlResult["count"].AsValuedNode();
long predicateCount = count != null?count.AsInteger() : 0;
// For each predicate with predicateCount > _minValuesPerPredicateLimit add a new column and an optional filter in where clause
if (predicateCount <= _minValuesPerPredicateLimit)
{
continue;
}
predicateIndex++;
String predicateColumnName = GetColumnName(predicate, entitiesQuery.Namespaces);
if (predicateColumnName == null)
{
continue;
}
selectColumns.Add(predicateColumnName);
optionalFilters.AppendLine(" OPTIONAL { @subject @predicate" + predicateIndex + " ?" + predicateColumnName + " }");
entitiesQuery.SetParameter("predicate" + predicateIndex, predicate);
}
if (selectColumns.Count == 1)
{
throw new RdfQueryException("No predicates which matched the criteria were found so an entities query cannot be generated");
}
entitiesQuery.CommandText = "SELECT DISTINCT ";
foreach (String column in selectColumns)
{
entitiesQuery.CommandText += "?" + column + " ";
}
entitiesQuery.CommandText += @"
WHERE
{
";
entitiesQuery.AppendSubQuery(initialQuery);
entitiesQuery.CommandText += optionalFilters.ToString();
entitiesQuery.CommandText += @"
}";
this.Information = "Generated Entities Query with " + (selectColumns.Count - 1) + " Predicate Columns";
this.OutputTableQuery = entitiesQuery.ToString();
}
catch (Exception)
{
this.OutputTableQuery = null;
throw;
}
return(this.OutputTableQuery);
}
