/// <summary>
/// Creates the projection part of the SPARQL query - the part that specifies which data to return back.
/// </summary>
/// <param name="sb">A <see cref="StringBuilder"/> into which the projection is inserted.</param>
private void CreateProjection(StringBuilder sb)
{
string distinct = Expressions.ContainsKey("Distinct") ? "DISTINCT " : String.Empty;
//Can use REDUCED if Distinct not specified
if (distinct.Equals(String.Empty))
{
if (Expressions.ContainsKey("Reduced"))
{
distinct = "REDUCED ";
}
}
if (Expressions.ContainsKey("Select"))
{
BuildProjection(Expressions["Select"]);
}
sb.Append("SELECT " + distinct);
if (Expressions.ContainsKey("GroupBy"))
{
throw new NotSupportedException("Group By is not supported by VDS.RDF.Linq");
}
// if it is of the form "from a in b select a"
if (ProjectionParameters.Count == 0)
{
foreach (MemberInfo mi in OwlClassSupertype.GetAllPersistentProperties(typeof(T)))
{
sb.Append(" ?");
sb.Append(mi.Name);
}
}
else
// if it is of the form "from a in b select new {a.c, a.d, a.e}" then add c,d,e to the projection
{
foreach (MemberInfo mi in ProjectionParameters)
{
sb.Append(" ?");
sb.Append(mi.Name);
}
}
// add a parameter to get back the instance URI to allow relationship tracking etc
sb.AppendLine(" $" + GetInstanceName());
}
/// <summary>
/// Creates the where clause of the SPARQL query - the part that indicates what the properties of selected objects should be.
/// </summary>
/// <param name="sb">A <see cref="StringBuilder"/> into which the SPARQL should be inserted.</param>
private void CreateWhereClause(StringBuilder sb)
{
// if using an identity projection then every available property of the type must be returned
bool isIdentityProjection = OriginalType == typeof(T);
// if there is no where clause then we want every instance back (and we won't be filtering)
// the logic around this is a little tricky (or debatable) -
// Given that you could have instances that are partially complete in the triple store (i.e. not all triples are present)
// you need to be able to ensure that a query that does not explicitly include the missing properties does not
// exclude any instances where those properties are missing.
// I've reasoned that if you perform an identity projection, then you're saying "get me whatever you can", whereas if
// you specifically request a certain property (via a projection) then you really must want a value for that, and thus
// instances must be excluded where there is no value _known_ - Hence the '|| IsIdentityProjection'.
bool getAnythingThatYouCan = !(Expressions.ContainsKey("Where")) || isIdentityProjection /* */;
// using "$" distinguishes this varName from anything that could be introduced from the properties of the type
// therefore the varName is 'safe' in the sense that there can never be a name clash.
string varName = "$" + GetInstanceName();
sb.Append("WHERE {\n");
// if parameters have been defined somewhere. If using an identity projection then we will not be getting anything from projectionParameters
// if we have no WHERE expression, then we also won't be getting anything from queryGraphParameters
var parameters = new List <MemberInfo>(QueryGraphParameters.Union(ProjectionParameters));
if (parameters.Count == 0)
{
// is it an identity projection? If so, place all persistent properties into parameters
if (isIdentityProjection)
{
foreach (PropertyInfo info in OwlClassSupertype.GetAllPersistentProperties(OriginalType))
{
parameters.Add(info);
}
}
}
// if (parameters.Count > 0)
// {
sb.AppendFormat("{0} a {1}:{2} .\n", varName, OriginalType.GetOntology().Prefix,
OriginalType.GetOwlResource().RelativeUriReference);
// }
// else
// {
// // I don't think there is any way to get into to this point unless the object is persistent, but has no
// throw new ApplicationException(
// "No persistent properties defined on the entity. Unable to generate a query.");
// }
//
// temp var to get the object variables list
IEnumerable <MemberInfo> args;
// a temp string to get the tripleFormat that will be used to generate query triples.
string tripleFormat = "OPTIONAL{{{0} {1}:{2} ?{3} .}}\n";
if (!getAnythingThatYouCan)
{
tripleFormat = "{0} {1}:{2} ?{3} .\n";
}
if (isIdentityProjection)
{
args = OwlClassSupertype.GetAllPersistentProperties(OriginalType);
}
else
{
args = parameters;
}
foreach (MemberInfo arg in args)
{
// The ontology and prefix assigned to a class property need not match those assigned to the class itself.
// e.g. The class could have a property which maps to foaf:name, or dc:title.
OwlResourceAttribute ora = arg.GetOwlResource();
sb.AppendFormat(tripleFormat,
varName,
AttributeExtensions.GetOntologyPrefix(ora.OntologyName), //WAS: originalType.GetOntology().Prefix,
ora.RelativeUriReference,
arg.Name);
}
if (!string.IsNullOrEmpty(PropertyReferenceTriple))
{
sb.AppendLine(PropertyReferenceTriple);
}
if (!string.IsNullOrEmpty(FilterClause))
{
sb.AppendFormat("FILTER( {0} )\n", FilterClause);
}
sb.Append("}\n");
}
