Question

I’m trying to start using LINQ and specifically LINQ to SQL but I’m having some difficulties

I’ve tried this with SqlMetal and now using the database table designer in Visual Studio and I keep getting similar errors, like in this code, using the data context I created with the database layout designer in VS2008.

using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.Web.UI; using System.Web.UI.WebControls;  public partial class _Default : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) {     if (Page.IsPostBack)     {         string usn = UserNameBox.Text;         string pss = PassBox.Text;          if (usn == '' || pss == '')             return;          DataClassesDataContext dc = new DataClassesDataContext();         var user = from u in User                    where u.UserName == usn                    select u;      } } } 

I get an error on the where saying: Could not find an implementation of the query pattern for source type ‘System.Security.Principal.IPrincipal’. And also: ‘Where’ not found.

I had something similar to this when I tried to use the results of SqlMetal. I deleted that source and started over using the designer. I must be missing something here but I can’t figure out what. Shouldn’t the tables implement what I need since I’m using LINQ to SQL, or do I need to do something extra to make that happen?

Answer 1

Try

var user = from u in dc.User                    where u.UserName == usn                    select u;