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);
}
}
