linq - Can't perform Create, Update or Delete operations on Table because it has no primary key

Question

I've been trying to insert row in the table having an identity column RequestID (which is primary key as well)

    HelpdeskLog logEntry = new HelpdeskLog { RequestBody = message.Body };
    if (attachment != null)
        logEntry.Attachments = Helper.StreamToByteArray(attachment.ContentStream);
    Database.HelpdeskLogs.InsertOnSubmit(logEntry);

But my code inevitably throws following error

Can't perform Create, Update or Delete operations on Table because it has no primary key.

despite primary key column exists indeed

That's what I tried to do:

1. To look in debugger the value of identity column being inserted in object model. It is 0
2. To insert manually (with SQL) fake values into table - works fine, identity values generated as expected
3. To assure if SQLMetal has generated table map correctly . All OK, primary key attribute is generated properly

Nevertheless, neither of approaches helped. What's the trick, does anybody know?

Answer 1

I've also had this problem come up in my C# code, and realized I'd forgotten the IsPrimaryKey designation:

  [Table (Name = "MySessionEntries" )]
  public class SessionEntry
  {
     [Column(IsPrimaryKey=true)]  // <---- like this
     public Guid SessionId { get; set; }
     [Column]
     public Guid UserId { get; set; }
     [Column]
     public DateTime Created { get; set; }
     [Column]
     public DateTime LastAccess { get; set; }
  }

this is needed even if your database table (MySessionEntries, in this case) already has a primary key defined, since Linq doesn't automagically find that fact out unless you've used the linq2sql tools to pull your database definitions into visual studio.