public override void SetObjectOperator(ResultOperatorBase resultOperator)
{
base.SetObjectOperator(resultOperator);
if (ObjectVariable != null)
{
if (resultOperator is AnyResultOperator)
{
// When using x.Any(), we add a LIMIT 1 the query results in the SparqlQueryGenerator.
// When using .Any(x => ..), the variable x is locally scoped and cannot be
// used in outer queries. Therefore do not need to actually select it.
// This avoids issues with Stardog:
// https://community.stardog.com/t/sparql-union-only-working-with-inferencing-enabled/1040/9
}
else if (resultOperator is AverageResultOperator)
{
var aggregate = new AverageAggregate(new VariableTerm(ObjectVariable.Name));
SetObjectVariable(aggregate.AsSparqlVariable(), true);
}
else if (resultOperator is CountResultOperator)
{
var aggregate = new CountDistinctAggregate(new VariableTerm(ObjectVariable.Name));
SetObjectVariable(aggregate.AsSparqlVariable(), true);
}
else if (resultOperator is FirstResultOperator)
{
// "Using LIMIT and OFFSET to select different subsets of the query solutions
// will not be useful unless the order is made predictable by using ORDER BY."
// Source: https://www.w3.org/TR/2013/REC-sparql11-query-20130321/#modOffset
// Therefore, if no ordering exists we add an ordering on the current subject
// to make the query result predictable.
if (!QueryModel.BodyClauses.OfType <OrderByClause>().Any())
{
OrderBy(SubjectVariable);
}
else
{
// In case the order was make explicit, we have to do nothing.
}
Limit(1);
}
else if (resultOperator is LastResultOperator)
{
// "Using LIMIT and OFFSET to select different subsets of the query solutions
// will not be useful unless the order is made predictable by using ORDER BY."
// Source: https://www.w3.org/TR/2013/REC-sparql11-query-20130321/#modOffset
// Therefore, if no ordering exists we add an ordering on the current subject
// to make the query result predictable.
if (!QueryModel.BodyClauses.OfType <OrderByClause>().Any())
{
OrderByDescending(SubjectVariable);
}
else
{
// Inverting the direction of the first ordering is handled in SparqlQueryModelVisitor.VisitOrdering().
// This is because the orderings are not necessarily processed *before* the result operators..
}
Limit(1);
}
else if (resultOperator is MaxResultOperator)
{
var aggregate = new MaxAggregate(new VariableTerm(ObjectVariable.Name));
SetObjectVariable(aggregate.AsSparqlVariable(), true);
}
else if (resultOperator is MinResultOperator)
{
var aggregate = new MinAggregate(new VariableTerm(ObjectVariable.Name));
SetObjectVariable(aggregate.AsSparqlVariable(), true);
}
else if (resultOperator is SumResultOperator)
{
var aggregate = new SumAggregate(new VariableTerm(ObjectVariable.Name));
SetObjectVariable(aggregate.AsSparqlVariable(), true);
}
else if (resultOperator is OfTypeResultOperator)
{
OfTypeResultOperator ofType = resultOperator as OfTypeResultOperator;
RdfClassAttribute type = ofType.SearchedItemType.TryGetCustomAttribute <RdfClassAttribute>();
if (type == null)
{
throw new ArgumentException("No RdfClass attrribute declared on type: " + ofType.SearchedItemType);
}
SparqlVariable s = ObjectVariable;
SparqlVariable p = VariableGenerator.CreatePredicateVariable();
SparqlVariable o = VariableGenerator.CreateObjectVariable();
WhereResource(s, p, o);
WhereResourceOfType(o, ofType.SearchedItemType);
}
else if (resultOperator is SkipResultOperator)
{
SkipResultOperator op = resultOperator as SkipResultOperator;
Offset(int.Parse(op.Count.ToString()));
}
else if (resultOperator is TakeResultOperator)
{
TakeResultOperator op = resultOperator as TakeResultOperator;
Limit(int.Parse(op.Count.ToString()));
}
else
{
throw new NotImplementedException(resultOperator.ToString());
}
}
}
private SparqlVariable BuildMemberAccess(MemberExpression memberExpression, IGraphPatternBuilder patternBuilder)
{
MemberInfo member = memberExpression.Member;
// If we do access a member of a system type, like string.Length we actually select the
// the declaring member and invoke a SPARQL built in call to get the value.
if (member.IsBuiltInCall())
{
MemberExpression parentMember = memberExpression.Expression as MemberExpression;
return(BuildMemberAccess(parentMember, patternBuilder));
}
else if (memberExpression.Expression is MemberExpression)
{
MemberExpression parentMember = memberExpression.Expression as MemberExpression;
// Note: When we build an optional property path, we consider the relation to the
// parent properties of the accessed property to be non-optional.
IGraphPatternBuilder builder = member.IsUriType() ? patternBuilder : PatternBuilder;
// We might encounter property paths (i.e. contact.Organization.Name). Therefore,
// implement the parent expression of the current member recursively..
SparqlVariable po = BuildMemberAccess(parentMember, builder);
// If we are building a node on a property path (parentExpression != null), we associate
// the object variable with the parent expression so that it becomes the subject of the parent.
VariableGenerator.SetSubjectVariable(memberExpression, po);
}
if (member.IsUriType())
{
// When we access the .Uri member of a resource we do not need a property mapping and return the subject as the bound variable.
// We create a triple pattern describing the resource in the local scope just in case it has not been described yet.
// Todo: Improve. Check if triples actually need to be asserted.
SparqlVariable s = VariableGenerator.TryGetSubjectVariable(memberExpression) ?? SubjectVariable;
SparqlVariable p = VariableGenerator.CreatePredicateVariable();
SparqlVariable o = VariableGenerator.CreateObjectVariable(memberExpression);
patternBuilder.Where(t => t.Subject(s).Predicate(p).Object(o));
VariableGenerator.SetSubjectVariable(memberExpression, s);
return(s);
}
else if (memberExpression.Expression is QuerySourceReferenceExpression)
{
QuerySourceReferenceExpression querySource = memberExpression.Expression as QuerySourceReferenceExpression;
if (VariableGenerator.TryGetSubjectVariable(memberExpression) == VariableGenerator.GlobalSubject)
{
// In case the accessed member is the global query subject (i.e. from x select x.Y)..
SparqlVariable s = VariableGenerator.TryGetSubjectVariable(querySource);
SparqlVariable o = VariableGenerator.GlobalSubject;
if (s == null)
{
s = VariableGenerator.CreateSubjectVariable(querySource);
BuildMemberAccess(memberExpression, patternBuilder, member, s, o);
}
return(o);
}
else
{
// Otherwise we are accessing a member of the globale query subject (i.e. from x where x.Y select x)
SparqlVariable s = VariableGenerator.TryGetSubjectVariable(querySource) ?? VariableGenerator.GlobalSubject;
SparqlVariable o = VariableGenerator.TryGetObjectVariable(memberExpression) ?? VariableGenerator.CreateObjectVariable(memberExpression);
BuildMemberAccess(memberExpression, patternBuilder, member, s, o);
return(o);
}
}
else
{
SparqlVariable s = VariableGenerator.TryGetSubjectVariable(memberExpression) ?? VariableGenerator.CreateSubjectVariable(memberExpression);
SparqlVariable o = VariableGenerator.TryGetObjectVariable(memberExpression) ?? VariableGenerator.CreateObjectVariable(memberExpression);
BuildMemberAccess(memberExpression, patternBuilder, member, s, o);
return(o);
}
}
