public void GetMyData(string sortFieldName)
{
    var query = db.MyEntity;
    var orderedQuery = query.OrderBy(x => x.FIELD_DATE);
    switch (sortFieldName)
    {
         case "FIELD_STRING":
             orderedQuery = query.OrderBy(x => x.FIELD_STRING); break;
         case "FIELD_INT":
             orderedQuery = query.OrderBy(x => x.FIELD_INT); break;
         case "FIELD_DATE":
             orderedQuery = query.OrderBy(x => x.FIELD_DATE); break;
    }

    //...some logic

}