Question

I am just starting to use linq to sql for data access. It is working fine for read only. But it does not work for update. I have been reading the threads over several forums. It is clear that anonymous types (in my case var) cannot be updated. I cannot find what I should replace the var with and where I find it. I will appreciate any help.

Below is the code. The exception is

Error 1 Property or indexer ‘AnonymousType#1.date_last_logon’ cannot be assigned to — it is read only

fmcsaDataContext db = new fmcsaDataContext();
//  DataTable _UserTable;
UserModel _UserModel = new UserModel();

var users  = from u in db.FMCSA_USERs
             where u.USER_NAME == pName && u.ACTIVE == true
             select new
             {
                  date_last_logon = u.DATE_LAST_LOGON,
                  date_current_logon = u.DATE_CURRENT_LOGON,
                  failed_login = u.FAILED_LOGIN,
             };

if (users.Count() == 0)
    return null;

foreach (var user in users)
{
    user.date_last_logon = user.date_current_logon;
}

Answer 1

This is the case for any ORM tool; you will have to use the entity types that LINQ-to-SQL generates for you when you make your .dbml file if you want to perform CRUD operations.

Also, be aware that your query is being executed twice and is not concurrently safe; calling Count() executes your query with a Count aggregate in the database, then looping over it executes the query again, this time bringing back results. Given what you’re doing, this may be better:

var users  = (from u in db.FMCSA_USERs
              where u.USER_NAME == pName && u.ACTIVE == true

              select u).ToList(); // This executes the query and materializes
                                  // the results into a List<FMCSA_USER>

if (users.Count == 0) return null;

foreach (var user in users)
{
    user.date_last_logon = user.date_current_logon;
}

db.SaveChanges();