Is there a pattern using Linq to dynamically create a filter?

Question

Is there a pattern using Linq to dynamically create a filter?

I have the need to create custom filtering on a list, in the past I would just dynamically create the SQL...it doesn't seem like this is possible with Linq.

Answer 1

Check out the Dynamic Linq Library from ScottGu's blog:

For example, below is a standard type-safe LINQ to SQL VB query that retrieves data from a Northwind database and displays it in a ASP.NET GridView control:

Dim Northwind As New NorthwindDataContext Dim query = From q In Northwind.Products Where p.CategoryID = 2 And p.UnitPrice > 3 Order By p.SupplierID Select p  Gridview1.DataSource = query GridView1.DataBind() 

Using the LINQ DynamicQuery library I could re-write the above query expression instead like so

Dim Northwind As New NorthwindDataContext Dim query = Northwind.Products .where("CategoryID=2 And UnitPrice>3") . OrderBy("SupplierId") Gridview1.DataSource = query GridView1.DataBind() 

Notice how the conditional-where clause and sort-orderby clause now take string expressions instead of code expressions. Because they are late-bound strings I can dynamically construct them. For example: I could provide UI to an end-user business analyst using my application that enables them to construct queries on their own (including arbitrary conditional clauses).