我有两个简单的清单:
public partial class Visitor
{
public Visitor()
{
this.Visits = new HashSet<Visit>();
}
public int Id { get; set; }
public int PermitId { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public string MiddleName { get; set; }
public bool IsValid { get; set; }
public System.DateTime RegistrationDate { get; set; }
public byte[] Picture { get; set; }
public virtual ICollection<Visit> Visits { get; set; }
}
public partial class Visit
{
public int Id { get; set; }
public int VisitType { get; set; }
public System.DateTime VisitDate { get; set; }
public Nullable<int> Visitor_Id { get; set; }
public virtual Visitor Visitor { get; set; }
}
在WCF方法中,我编写了查询并试图返回结果:
public List<Visitor> AllVisitors()
{
using (var te = new TurnstileDbEntities())
{
te.Configuration.ProxyCreationEnabled = false;
return (List<Visitor>) te.Visitors.SelectMany(visitors => te.Visits
.Where(o => o.Visitor_Id == visitors.Id)
.DefaultIfEmpty(), (visitors, visit) => new {visitors, visit});
}
}
好了,正如我所料,我收到了一个例外:
附加信息:无法将对象“ System.Data.Entity.Infrastructure.DbQuery
1[<>f__AnonymousType0
2 [TurnstileWcfService.Visitor,TurnstileWcfService.Visit]]”类型转换为“ System.Collections.Generic.List`1 [TurnstileWcfService.Visitor]” 。
好的。我改写这个。宣布新班级。
public class JoinResult
{
public Visitor Visitors { get; set; }
public Visit Visits { get; set; }
}
并重写方法。
public IQueryable AllVisitors()
{
using (var te = new TurnstileDbEntities())
{
te.Configuration.ProxyCreationEnabled = false;
return te.Visitors.Join(te.Visits,
r => r.Id, a => a.Visitor_Id, (r, a) => new JoinResult
{
Visits = a,
Visitors = r
});
}
}
这是可行的,但我想使用Visitor类。访客类包含ICollectionVisits,我想填充它。在不声明新类的情况下如何在Linq语句中执行此操作?
我也可以在下面的代码中得到想要的东西。但是我不喜欢这样。
var visitors = te.Visitors.ToList();
foreach (var item in visitors)
{
item.Visits = te.Visits.Where(v => v.Visitor_Id == item.Id).ToList();
}
Gert Arnold是正确的,请尝试:
List<Visitor> visitors = te.Visitors.Include(v => v.Visits).ToList();
编辑我也按如下方式工作:
List<Visitor> visitors = te.Visitors.Include("Visits").ToList();
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我来说两句