"Expression type 'NhDistinctExpression' is not supported by this SelectClauseVisitor." - 使用查询语法

Question

给定以下表达式，我如何才能获得不同的场地列表，而不会出现令人讨厌的 "Expression type 'NhDistinctExpression' is not supported by this SelectClauseVisitor." 错误？

    public Dictionary<int, string> GetScheduledVenuesFuture()
    {
        var venues = from v in _sp.CurrentSessionOn(DatabaseName.MyDB).Query<Venue>()
                     join s in _sp.CurrentSessionOn(DatabaseName.MyDB).Query<ScheduledClass>()
                             on v.VenueId equals s.Venue.VenueId
                     where s.CourseDate >= _cac.Now
                             && s.Closed == false
                             && s.Canceled == false

                     select new
                     {
                         v.VenueId,
                         v.Name
                     };

        return venues.ToDictionary(v => v.VenueId, v => v.Name);
    }

我试过设置

        return venues.ToDictionary(v => v.VenueId, v => v.Name);

通过以下方式区分：

        return venues.Distinct().ToDictionary(v => v.VenueId, v => v.Name);

但这会引发错误。我还尝试将整个查询语法语句包围在括号中，并在其末尾放置一个 .Distinct() ，但这也导致了同样的错误。

Answer 1

我最终以另一种方式解决了这个问题：

    public class ScheduledVenueDTO
    {
        public int VenueId { get; set; }
        public string Name { get; set; }
    }

    public Dictionary<int, string> GetScheduledVenuesFuture()
    {
        var venues = from v in _sp.CurrentSessionOn(DatabaseName.SMS).Query<Venue>()
                     join s in _sp.CurrentSessionOn(DatabaseName.SMS).Query<ScheduledClass>()
                             on v.VenueId equals s.Venue.VenueId
                     where s.CourseDate >= _cac.Now
                             && s.Closed == false
                             && s.Canceled == false
                     select new
                     {
                         v.VenueId,
                         v.Name
                     };

        var svd = venues
            .GroupBy(v => new { v.VenueId, v.Name})
            .Select(v => new ScheduledVenueDTO() {
                VenueId = v.Key.VenueId,
                Name = v.Key.Name
            });

        return svd.ToDictionary(v => v.VenueId, v => v.Name);
    }

我只是创建了一个新的 DTO，并使用 groupBy 为该 DTO 注入了唯一不同的场所。

"Expression type 'NhDistinctExpression' is not supported by this SelectClauseVisitor." - 使用查询语法

"Expression type 'NhDistinctExpression' is not supported by this SelectClauseVisitor." - with Query Syntax

c#

linq-query-syntax