/// <summary>
/// Applies the Filter over the results of evaluating the inner pattern.
/// </summary>
/// <param name="context">Evaluation Context.</param>
/// <returns></returns>
public sealed override BaseMultiset Evaluate(SparqlEvaluationContext context)
{
INode term = _term.Evaluate(null, 0);
// First take appropriate pre-filtering actions
if (context.InputMultiset is IdentityMultiset)
{
// If the Input is Identity switch the input to be a Multiset containing a single Set
// where the variable is bound to the term
context.InputMultiset = new Multiset();
Set s = new Set();
s.Add(RestrictionVariable, term);
context.InputMultiset.Add(s);
}
else if (context.InputMultiset is NullMultiset)
{
// If Input is Null then output is Null
context.OutputMultiset = context.InputMultiset;
return(context.OutputMultiset);
}
else
{
if (context.InputMultiset.ContainsVariable(RestrictionVariable))
{
// If the Input Multiset contains the variable then pre-filter
foreach (int id in context.InputMultiset.SetIDs.ToList())
{
ISet x = context.InputMultiset[id];
try
{
if (x.ContainsVariable(RestrictionVariable))
{
// If does exist check it has appropriate value and if not remove it
if (!term.Equals(x[RestrictionVariable]))
{
context.InputMultiset.Remove(id);
}
}
else
{
// If doesn't exist for this set then bind it to the term
x.Add(RestrictionVariable, term);
}
}
catch (RdfQueryException)
{
context.InputMultiset.Remove(id);
}
}
}
else
{
// If it doesn't contain the variable then bind for each existing set
foreach (ISet x in context.InputMultiset.Sets)
{
x.Add(RestrictionVariable, term);
}
}
}
// Then evaluate the inner algebra
BaseMultiset results = context.Evaluate(InnerAlgebra);
if (results is NullMultiset || results is IdentityMultiset)
{
return(results);
}
// Filter the results to ensure that the variable is indeed bound to the term
foreach (int id in results.SetIDs.ToList())
{
ISet x = results[id];
try
{
if (!term.Equals(x[RestrictionVariable]))
{
results.Remove(id);
}
}
catch (RdfQueryException)
{
results.Remove(id);
}
}
if (results.Count > 0)
{
context.OutputMultiset = results;
}
else
{
context.OutputMultiset = new NullMultiset();
}
return(context.OutputMultiset);
}