/// <summary>
/// Executes the expression tree that is passed to it.
/// </summary>
/// <param name="expression">Expression Tree</param>
/// <param name="isEnumerable"></param>
/// <returns></returns>
internal static object Execute(Expression expression, bool isEnumerable)
{
// The expression must represent a query over the data source.
if (!IsQueryOverDataSource(expression))
{
throw new InvalidProgramException("No query over the data source was specified.");
}
// Find the call to Where() and get the lambda expression predicate.
var whereFinder = new InnermostWhereFinder();
var whereExpression = whereFinder.GetInnermostWhere(expression);
var lambdaExpression = (LambdaExpression)((UnaryExpression)(whereExpression.Arguments[1])).Operand;
// Send the lambda expression through the partial evaluator.
lambdaExpression = (LambdaExpression)Evaluator.PartialEval(lambdaExpression);
// Get the place name(s) to query the Web service with.
var lf = new TrackFinder(lambdaExpression.Body);
var locations = lf.TrackNames;
if (locations.Count == 0)
{
throw new InvalidQueryException("You must specify at least one place name in your query.");
}
// Call the Web service and get the results.
Track[] places = WebServiceHelper.GetTracks(locations);
// Copy the IEnumerable places to an IQueryable.
IQueryable <Track> queryablePlaces = places.AsQueryable();
// Copy the expression tree that was passed in, changing only the first
// argument of the innermost MethodCallExpression.
var treeCopier = new ExpressionTreeModifier(queryablePlaces);
var newExpressionTree = treeCopier.Visit(expression);
// This step creates an IQueryable that executes by replacing Queryable methods with Enumerable methods.
if (isEnumerable)
{
return(queryablePlaces.Provider.CreateQuery(newExpressionTree));
}
return(queryablePlaces.Provider.Execute(newExpressionTree));
}
static void Main(string[] args)
{
ExpressionTreeModifier modifier = new ExpressionTreeModifier();
Expression <Func <int, int, int, int> > expr = (a, b, c) => a + b * (c + 1);
Console.WriteLine(expr);
Console.WriteLine(expr.Compile()(1, 2, 3));
Expression <Func <int, int, int, int> > expr1 = modifier.VisitAndConvert(expr, "");
Console.WriteLine(expr1);
Console.WriteLine(expr1.Compile()(1, 2, 3));
Dictionary <string, object> constants = new Dictionary <string, object> {
{ "a", 1 }, { "d", 2 }, { "c", 3 }
};
LambdaExpression expr2 = (LambdaExpression)modifier.Modify(expr, constants);
Console.WriteLine(expr2);
Console.WriteLine(expr2.Compile()(1, 2, 3));
Console.ReadKey();
}