// 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());
}
private Func <object, T> GetSelectProj <T>(QueryModel queryModel)
{
Func <object, T> projector = (result) => (T)result;
if (this.visitor.IsSingleResult)
{
return(projector);
}
var proj = ProjectorBuildingExpressionTreeVisitor.BuildProjector <T>(queryModel.SelectClause.Selector);
projector = (result) => proj(new ResultObjectMapping(queryModel.MainFromClause, result));
return(projector);
}