public void WhereEqual(MemberExpression expression, ConstantExpression c)
{
if (c.Value == null)
{
// If we want to filter for non-bound values we need to mark the properties as optional.
SparqlVariable so = BuildMemberAccessOptional(expression);
// TODO: If we filter a resource, make sure it has been described with variables in the local scope.
// Comparing with null means the variable is not bound.
PatternBuilder.Filter(e => !e.Bound(so.Name));
}
else if (c.Type.IsValueType || c.Type == typeof(string))
{
if (expression.Member.DeclaringType == typeof(string))
{
BuildMemberAccess(expression);
// If we are comparing a property of string we need to implement SPARQL built-in call on the variable such as STRLEN..
BuildBuiltInCall(expression, e => e == c.AsNumericExpression());
}
else
{
// TODO: The default value for a property may be overridden with the DefaultValue attribute.
object defaultValue = TypeHelper.GetDefaultValue(c.Type);
// If the value IS the default value, WhereEquals includes the default value and therefore includes non-bound values..
if (c.Value.Equals(defaultValue))
{
// If we want to filter for non-bound values we need to mark the properties as optional.
SparqlVariable o = BuildMemberAccessOptional(expression);
// Mark the variable to be coalesced with the default value when selected.
CoalescedVariables[o] = Expression.Constant(defaultValue).AsLiteralExpression();
// Comparing with null means the variable is not bound.
PatternBuilder.Filter(e => e.Variable(o.Name) == c.AsLiteralExpression() || !e.Bound(o.Name));
}
else
{
// If we want to filter bound literal values, we still write them into a variable so they can be selected.
SparqlVariable o = BuildMemberAccess(expression);
PatternBuilder.Filter(e => e.Variable(o.Name) == c.AsLiteralExpression());
}
}
}
else
{
// We are comparing reference types / resources against a bound value here.
SparqlVariable so = BuildMemberAccess(expression);
// TODO: If we filter a resource, make sure it has been described with variables in the local scope.
PatternBuilder.Filter(e => e.Variable(so.Name) == c.AsIriExpression());
}
}
public void WhereNotEqual(SparqlVariable v, ConstantExpression c)
{
if (c.Value == null)
{
PatternBuilder.Filter(e => e.Bound(v.Name));
}
else if (c.Type.IsValueType || c.Type == typeof(string))
{
PatternBuilder.Filter(e => e.Variable(v.Name) != c.AsLiteralExpression());
}
else
{
PatternBuilder.Filter(e => e.Variable(v.Name) != c.AsIriExpression());
}
}
public override void OnBeforeSelectClauseVisited(Expression selector)
{
base.OnBeforeSelectClauseVisited(selector);
QuerySourceReferenceExpression sourceExpression = selector.TryGetQuerySourceReference();
if (sourceExpression != null)
{
// Register the query source with the global variable for sub-queries.
SparqlVariable s = VariableGenerator.TryGetSubjectVariable(sourceExpression) ?? VariableGenerator.GlobalSubject;
// Assert the object type.
if (sourceExpression.Type.IsSubclassOf(typeof(Resource)))
{
WhereResourceOfType(s, sourceExpression.Type);
}
if (selector is MemberExpression)
{
MemberExpression memberExpression = selector as MemberExpression;
SparqlVariable o = VariableGenerator.CreateObjectVariable(memberExpression);
// Select all triples having the resource as subject.
SetSubjectVariable(s);
SetObjectVariable(o, true);
// If the member expression is not selected in the WHERE block, we add it here.
// Scenarios:
// - from x in Model.AsQueryable<X>() select x.B
// - from x in Model.AsQueryable<X>() where x.A select x.B
string e = memberExpression.ToString();
if (!QueryModel.BodyClauses.OfType <WhereClause>().Any(c => c.Predicate.ToString().Contains(e)))
{
// We select the member without a constraint on its value.
QueryModel.BodyClauses.Add(new WhereClause(memberExpression));
// Since there is no constraint on the member, we also need to select the ones that are not bound.
Type memberType = memberExpression.Member.GetMemberType();
// TODO: There might be a different default value on the member using the DefaultValue() attribute.
object defaultValue = TypeHelper.GetDefaultValue(memberType);
if (defaultValue != null && memberType != typeof(string))
{
ConstantExpression coalescedValue = Expression.Constant(defaultValue);
// Mark the variable to be coalesced with the default value when selected.
CoalescedVariables[o] = coalescedValue.AsLiteralExpression();
}
}
}
else if (QueryModel.HasNumericResultOperator())
{
// If we have a numeric result operator on the root query, make the
// subject variable known so that the model visitor can handle it.
SetSubjectVariable(s);
}
}
}
