EXISTS query in Dynamic Linq

[Richard]

I have the following simple query in SQL:

SELECT A.*
FROM Products AS A
WHERE EXISTS (SELECT B.Category_Id
              FROM Categories AS B
              WHERE B.Category_Type = 'Stationary'
              AND B.Category_Id = A.Category_Id)

I successfully converted this to a Linq query as follows:

from a in Products
where (from b in Categories
where b.Category_Type == 'Stationary'
select b.Category_Id).Contains(a.Category_Id)
select a

However, the 'Stationary' value should be dynamic. Therefore, I downloaded the Dynamic.vb library for inclusion in my project (via Includes System.Linq.Dynamic) so I can then dynamically build this query. I started with:

Dim query = from a in Products
query.where(...

and this is where I got stuck! Can anyone assist in making this a dynamic query where I can populate the Category_Type based on user input?

[PetarP]

Hi Richard,

If the stationary is a value why don't you pass it as a parameter like this:

Dim sampleParameter As String = "User Input"
from a in Products
where (from b in Categories
where b.Category_Type == sampleParameter
select b.Category_Id).Contains(a.Category_Id)
select a

You only need to put the user input into the sampleParameter parameter. The dynamic linq is used to dynamically switch between the things you query. So for example you can once query against the Category_Type and the next time query on Category_Id. As for your case if I have understood it correctly I believe you don't need to use any dynamic Linq.

Greetings,
Petar
the Telerik team