Issue with Linq To Entities in C#

I am trying to use Linq to Entites to convert a Guid in my database to a string. I have a CheckBoxListDTO. This DTO has 2 properties: Text and Value. They are both String data types. I have an error when I just try to do a .ToString() saying that Linq does not allow ToString() for Entities. I then put .AsEnumerable() for my tables and it works. Will this way make it slower if I start having a lot of data in my database? Is there a better way around this?
My DTO: public class CheckBoxListDTO { public string Text { get; set; } public string Value { get; set;} } Linq Code that works: result.businessIdList = (from ac in cd.tbl_AlertID.AsEnumerable() from cdd in cd.tbl_Data.AsEnumerable() where ac.mainId == cdd.mainId && ac.EmailI ...