Linq在查询中解析时未被识别

你应该首先使用 FirstOrDefault() 然后解析它。否则,linq仍在尝试构建select语句。之后 FirstOrDefault ToList

应该是这样的:

public static UserDetails GetUser(UserDetails userde)
{
    var usr = from u in db.Users
              join r in db.Roles on u.RoleId equals r.IdRole
              where u.Email == userde.Email && u.Active == true

              select new UserDetails { Firstname = u.Firstname,
                  Surname = u.Surname,
                  Email = u.Email,
                  Function = u.Function,
                  Password = u.Password,
                  Salt = u.Salt,

                  // store the database-value in another property
                  UserrolesUnparsed = r.Role1
                  };

    // get the database-results
    UserDetails details = usr.FirstOrDefault();

    // parse the database-value and set it to the property you want to
    details.Userroles = (UserRoles)Enum.Parse(typeof(UserRoles), details.UserrolesUnparsed);

    return details;

}