NHibernate Linq with subquery返回'当子查询没有引入EXISTS'时，只能在

我正试图得到以下查询工作:

var users = session.Query<PersonUser>()
.Select(u => new User()
{
    Id = u.UserId,
    FirstName = u.UserFirstName,
    Surname = u.UserSurname,
    ActiveRoles = u.Roles.Select(rr => new Role() { Id = rr.RoleId, DisplayName = rr.RoleName })
})
.ToList();

当我执行查询时，我得到以下内容:

NHibernate.Exceptions.GenericADOException occurred
  Message=could not execute query
[ select personuser0_.USER_ID as col_0_0_, personuser0_.USER_FIRSTNAME as col_1_0_, personuser0_.USER_SURNAME as col_2_0_, (select personrole2_.ROLE_ID, personrole2_.ROLE_NAME from PERSON_ROLE_USER roles1_, PERSON_ROLE personrole2_ where personuser0_.USER_ID=roles1_.USER_ID and roles1_.ROLE_ID=personrole2_.ROLE_ID) as col_3_0_ from PERSON_USER personuser0_ ]
[SQL: select personuser0_.USER_ID as col_0_0_, personuser0_.USER_FIRSTNAME as col_1_0_, personuser0_.USER_SURNAME as col_2_0_, (select personrole2_.ROLE_ID, personrole2_.ROLE_NAME from PERSON_ROLE_USER roles1_, PERSON_ROLE personrole2_ where personuser0_.USER_ID=roles1_.USER_ID and roles1_.ROLE_ID=personrole2_.ROLE_ID) as col_3_0_ from PERSON_USER personuser0_]
  Source=NHibernate
  SqlString=select personuser0_.USER_ID as col_0_0_, personuser0_.USER_FIRSTNAME as col_1_0_, personuser0_.USER_SURNAME as col_2_0_, (select personrole2_.ROLE_ID, personrole2_.ROLE_NAME from PERSON_ROLE_USER roles1_, PERSON_ROLE personrole2_ where personuser0_.USER_ID=roles1_.USER_ID and roles1_.ROLE_ID=personrole2_.ROLE_ID) as col_3_0_ from PERSON_USER personuser0_
InnerException: System.Data.SqlClient.SqlException
       Message=Only one expression can be specified in the select list when the subquery is not introduced with EXISTS.
       Source=.Net SqlClient Data Provider
       ErrorCode=-2146232060
       Class=16
       LineNumber=1
       Number=116
       Procedure=""
       State=1

注:PersonUser和PersonRole为POCO数据库实体，User和Role为简单DTO。PersonUser.Roles是List映射的hasmanymany .

我怎样才能让NH正确地项目到User DTO，包括它的多对多关系到Role DTO?

非常感谢你的帮助!

var users = session.Query<PersonUser>()
    .Fetch(u => u.Roles).Eager
    .AsEnumerable()
    .Select(u => new User
    {
        Id = u.UserId,
        FirstName = u.UserFirstName,
        Surname = u.UserSurname,
        ActiveRoles = u.Roles.Select(rr => new Role { Id = rr.RoleId, DisplayName = rr.RoleName }).ToList()
    })
    .ToList();