public static Func <ResultObjectMapping, Func <T, T> > BuildAggregateProjector(QueryModel model, LambdaExpression aggregate)
{
var visitor = new ProjectorBuildingExpressionTreeVisitor <T>(aggregate, model.MainFromClause.ItemType);
var body = visitor.VisitExpression(aggregate);
return(Expression.Lambda <Func <ResultObjectMapping, Func <T, T> > >(body, visitor.ResultItemParameter).Compile());
}
// Call this method to get the projector. T is the type of the result (after the projection).
public static Func <ResultObjectMapping, T> BuildProjector(QueryModel model)
{
// The visitor gives us the projector's body. It simply replaces all QuerySourceReferenceExpressions with calls to ResultObjectMapping.GetObject<T>().
var selector = model.SelectClause.Selector;
Type resultTypeOverride = null;
var castOperator = model.ResultOperators.LastOrDefault(it => it is CastResultOperator) as CastResultOperator;
if (castOperator != null && selector.Type != castOperator.CastItemType)
{
resultTypeOverride = castOperator.CastItemType;
}
var allOperator = model.ResultOperators.LastOrDefault(it => it is AllResultOperator) as AllResultOperator;
if (allOperator != null)
{
resultTypeOverride = allOperator.Predicate.Type;
}
if (model.ResultOperators.Any(it => it is CountResultOperator))
{
resultTypeOverride = typeof(int);
}
if (model.ResultOperators.Any(it => it is LongCountResultOperator))
{
resultTypeOverride = typeof(long);
}
if (model.ResultOperators.Any(it => it is AnyResultOperator))
{
resultTypeOverride = typeof(bool);
}
var visitor = new ProjectorBuildingExpressionTreeVisitor <T>(selector, resultTypeOverride);
var body = visitor.VisitExpression(selector);
// Construct a LambdaExpression from parameter and body and compile it into a delegate.
//PERF: compile is slow
return(Expression.Lambda <Func <ResultObjectMapping, T> >(body, visitor.ResultItemParameter).Compile());
}