Getting Count() property in Dynamic Lambda Expression

Question

I almost got what I need but only one place where I stucked. I need to build fileCount = c.CPNDocs.Count() Dynamically in Lambda Expression. Code is below w

Answer 1

The Count() is not a property. It is an extension method implemented in a static class. This extension method is implemented at several places. Correct place depends on what are your classes inheriting from. To find the correct place you use the "go to definition" feature of Visual Studio.

e.g. for IQueryable.Count() the extension methods are implemented by System.Linq.Queryable static class as can be seen here → http://referencesource.microsoft.com/#System.Core/System/Linq/IQueryable.cs

So in order to encode the expression you need to encode a call to the extension method.

Much simpler way to generate expression trees from strings was shown quite early in a prototype published by Microsoft. Introductory article is available e.g. in Dynamic Expressions and Queries in LINQ

We use modified version of the original source of the automatic "string to linq" engine with success and it simplifies development a lot. By inspecting the source code of the System.Linq.Dynamic you can find exact way how to encode the expression. Link to the original source code available through NuGet is mentioned e.g. in Stack Overflow article Dynamic LINQ - Is There A .NET 4 Version?