protected override Expression VisitMethodCall(MethodCallExpression m)
{
if (m.Method.Name == "Project" && m.Method.DeclaringType == typeof(Extensions))
{
Expression projectionExpression = m.Arguments[0];
LambdaExpression projectionLambda = ExtractLambda(projectionExpression);
// Visit the lambda, essentially extracting the lambda's expression tree
Expression visitedMethodCall = Visit(projectionLambda.Body);
// Revisit the lambda's expression tree, replacing the lambda's parameter with the actual expression that results in the same return value
var parameterMap = new Dictionary<ParameterExpression, Expression>();
int lambdaParameterArgumentIndex = 1;
foreach (var parameter in projectionLambda.Parameters)
{
parameterMap.Add(parameter, m.Arguments[lambdaParameterArgumentIndex++]);
}
visitedMethodCall = new ParameterRebinder(parameterMap).Visit(visitedMethodCall);
return visitedMethodCall;
}
return base.VisitMethodCall(m);
}
protected override Expression VisitMethodCall(MethodCallExpression m)
{
Expression visitedMethodCall = null;
if (m.Method.Name == "Select")
{
_selectStack.Push(m);
}
if (m.Method.Name == "Project" && m.Method.DeclaringType == typeof(Extensions))
{
// Project() is expected to be invoked on an Expression<Func<In, Out>>,
// the expression can be contained in a local variable, a field, retrived from a method
// or any other expression tree as long as it can be compiled and executed to return a proper lambda
ParameterExpression selectParameter = GetSelectParameter(_selectStack.Peek());
LambdaExpression innerLambda = GetInnerLambda(m.Arguments[0], selectParameter.Type, m.Method.ReturnType);
// By returning the visited body of the lambda we ommit the call to Project()
// and the tree producing the selector lambda:
visitedMethodCall = Visit(innerLambda.Body);
// The lambda takes a parameter, this parameter must be replaced by the parameter provided for the seelct lambda
// Rebind parameter:
var map = new Dictionary <ParameterExpression, ParameterExpression>()
{
{
innerLambda.Parameters[0],
selectParameter
}
};
visitedMethodCall = new ParameterRebinder(map).Visit(visitedMethodCall);
}
if (visitedMethodCall == null)
{
visitedMethodCall = base.VisitMethodCall(m);
}
if (m.Method.Name == "Select")
{
_selectStack.Pop();
}
return(visitedMethodCall);
}
