c# - LINQ 中导航属性查询的 ArgumentException

Question

我在使用 Entity Framework 6 的 Visual Studio 2015 WPF 应用程序中有以下 LINQ 查询:

var query = Context.Services.AsQueryable();

Services 实体具有以下导航属性:

public virtual ICollection<ServiceStatu> ServiceStatus { get; set; }

一个服务可以有 0 个或多个 ServiceStatus。我正在尝试使用 Include 获取状态等于 7 的服务:

query = query.Include(x => x.ServiceStatus.Where(p => p.serviceStatusID == 7));

但是它抛出了这个异常:

An exception of type 'System.ArgumentException' occurred in EntityFramework.dll but was not handled in user code

Additional information: The Include path expression must refer to a navigation property defined on the type. Use dotted paths for reference navigation properties and the Select operator for collection navigation properties.

请注意，我曾尝试使用 JOIN 来执行此操作，但那很丑陋，所以我决定使用内置导航属性。

我做错了什么？谢谢。

Answer 1

不幸的是，您无法在 Include 调用中过滤导航属性。正如异常(exception)所说，您需要引用导航属性。要过滤您的导航属性，您需要将查询投影到匿名类型或 DTO，例如:

query = query.Include(x => x.ServiceStatus)
             .Select(s=>new {
                              //other properties that you need to project
                              Status=s.ServicesStatus.Where(p => p.serviceStatusID == 7)
                            });

一种在加载时过滤相关实体的方法是使用 Explicit Loading :

 var service= query.FistOrDefault();// this is an example to use a service instance
 context.Entry(service) 
        .Collection(b => b.ServiceStatus) 
        .Query() 
        .Where(ss => ss.Where(p => p.serviceStatusID == 7) 
        .Load();