protected Func <object, T> GetSelectProjector <T>(object firstResult, QueryModel queryModel)
{
Func <object, T> projector = (result) => result.Cast <T>();
if (ShouldBuildResultObjectMapping <T>(firstResult, queryModel))
{
var proj = ProjectorBuildingExpressionTreeVisitor.BuildProjector <T>(queryModel.SelectClause.Selector);
projector = (result) => proj(new ResultObjectMapping(queryModel.MainFromClause, result));
}
return(projector);
}
// Call this method to get the projector. T is the type of the result (after the projection).
public static Func <ResultObjectMapping, T> BuildProjector <T>(Expression selectExpression)
{
// This is the parameter of the delegat we're building. It's the ResultObjectMapping, which holds all the input data needed for the projection.
var resultItemParameter = Expression.Parameter(typeof(ResultObjectMapping), "resultItem");
// The visitor gives us the projector's body. It simply replaces all QuerySourceReferenceExpressions with calls to ResultObjectMapping.GetObject<T>().
var visitor = new ProjectorBuildingExpressionTreeVisitor(resultItemParameter);
var body = visitor.VisitExpression(selectExpression);
// Construct a LambdaExpression from parameter and body and compile it into a delegate.
var projector = Expression.Lambda <Func <ResultObjectMapping, T> >(body, resultItemParameter);
return(projector.Compile());
}