错误：无法在 LINQ to Entities 查询中构造实体或复杂类型

Question

我在使用 MVC 进行连接查询时遇到问题，我不知道为什么。

无法在 LINQ to Entities 查询中构造实体或复杂类型“Tusofona_Website.Models.site_noticias”。

我的控制器：

    private TusofonaDBs db = new TusofonaDBs();

    //
    // GET: /DestaquesMain/

    public ActionResult Index()
    {
        var query = (from sd in db.site_desquesnoticias
                    join sn in db.site_noticias on sd.IDNoticia equals sn.IDNoticia
                    where sn.Destaque == 1
                    select new site_noticias {
                        CorpoNoticia = sn.CorpoNoticia,
                        TituloNoticia = sn.TituloNoticia
                    }).ToList();

        //return View(db.site_desquesnoticias.ToList());
          return View(query);

    }

我的模特：

public class site_destaquesnoticias
{
    [Key]
    public Int32 IDDestaque { get; set; }
    public Int32 IDNoticia { get; set; }
    public string Foto { get; set; }


}

public class site_noticias
{
    [Key]
    public Int32 IDNoticia { get; set; }
    public string CorpoNoticia { get; set; }
    public string TituloNoticia { get; set; }
    public string Foto { get; set; }
    public Int32 Destaque { get; set; }
}

public class TusofonaDBs : DbContext
{
    public DbSet<site_destaquesnoticias> site_desquesnoticias { get; set; }
    public DbSet<site_noticias> site_noticias { get; set; }
}

谁能帮帮我？

Answer 1

您不能投影到映射实体上（请参阅this 答案）。

但是，您可以做几件事：

1) 选择匿名类型而不是实体，例如：

var query = (from sd in db.site_desquesnoticias
                    join sn in db.site_noticias on sd.IDNoticia equals sn.IDNoticia
                    where sn.Destaque == 1
                    select new {
                        CorpoNoticia = sn.CorpoNoticia,
                        TituloNoticia = sn.TituloNoticia
                    }).ToList();

2) 反转查询以直接选择 site_noticias。这取决于您要检索的查询和数据。例如，您可以查看以下内容是否可行并为您提供所需的数据：

var query = (from sd in db.site_desquesnoticias
                    join sn in db.site_noticias on sd.IDNoticia equals sn.IDNoticia
                    where sn.Destaque == 1
                    select sn).ToList();

3) 使用一些 DTO（数据传输对象）将您要选择的属性投影到：

   public class SiteNoticiasDTO{
     public string CorpoNoticia {get;set;}
     public string TituloNoticia {get;set;}
    }

var query = (from sd in db.site_desquesnoticias
                    join sn in db.site_noticias on sd.IDNoticia equals sn.IDNoticia
                    where sn.Destaque == 1
                    select new SiteNoticiasDTO {
                        CorpoNoticia = sn.CorpoNoticia,
                        TituloNoticia = sn.TituloNoticia
                    }).ToList();