how do i build dynamic linq queries at runtime using strings?

Question

This article talks about building dynamic queries using strings is it possible?

i tried

var ase = a.Select("NEW(activity_date as date)");

and it doesn't work

The type arguments for method 'System.Linq.Enumerable.Select(System.Collections.Generic.IEnumerable, System.Func)' cannot be inferred from the usage. Try specifying the type arguments explicitly.

C:\.....\filename.xaml.cs

how do i build dynamic linq queries at runtime using strings?

Answer 1

在linq samples目录中有一个很酷的Dynamic Linq库你可以使用，Scott Gu有一篇关于如何在这里使用它的相当不错的博客文章。

Answer 2

Yes you can have dynamic linq queries at runtime using strings. You need to use the ObjectQuery class as mentioned here and below is the code snippet to do this:

string queryString =
    @"SELECT VALUE product FROM AdventureWorksEntities.Products AS product";

// Call the constructor with the specified query and the ObjectContext.
ObjectQuery<Product> productQuery2 =
    new ObjectQuery<Product>(queryString, context);

foreach (Product result in productQuery2)
    Console.WriteLine("Product Name: {0}", result.Name);

ObjectQuery will validate the query against the LINQ model at the runtime and throws exception if it couldn't find some of the properties you are using in the query.