Data binding directly to a store query (DbSet, DbQuery, DbSqlQuery) is not supported

Question

Am coding on visual studio 2012 and using Entity Model as my Data layer. However, my drop down control with the Linq statement tend to throw an unhandled exception when the page tries to load (stated title above). Here is my code below;

using (AdventureWorksEntities dw = new AdventureWorksEntities())
        {
            ddlCon.DataSource = (from em in dw.Employees
                                 select new { em.Title, em.EmployeeID });

            ddlCon.DataTextField = "Title";
            ddlCon.DataValueField = "EmployeeID";
            ddlCon.DataBind();
            ddlCon.Items.Insert(0, new ListItem("--Select--", "--Select--"));
        }

1. I want to know why that error occurred
2. What should be the proper way to bind to a control when using LINQ?

Answer 1

The error is fairly clear - you can't bind directly to the query results, but need to populate some local collection instead.

The simplest way to do this is to convert it to a List<T>, via ToList():

 ddlCon.DataSource = (from em in dw.Employees
                             select new { em.Title, em.EmployeeID }).ToList();

Answer 2

Or if you want to avoid writing a LINQ expression you could just do this:

var dbContext = new EF.CustomerEntities();
gvCustomers.DataSource = dbContext.CustomersTable.ToList();