c# - 过滤导航属性实体框架，返回 NULL

Question

我正在尝试使用导航属性，但是当我使用它时出现错误

值不能为空。

这是可以理解的，因为 People 集合是 NULL，但为什么它是 NULL？

我真正想做的是通过 RequestorPersonID 选择请求者的名称（最后一个代码片段的最后一行）

public abstract class Person
{
    [Key]     
    public int PersonID { get; set; }         
    public string FirstName { get; set; }      
} 
public class Employee : Person
{
    public string Department { get; set; }
}
public class FrDetail
{
    [Key]
    public int FrID { get; set; }      
    public int RequestorPersonID { get; set; }
    virtual public IList<Person> People { get; set; }
}
public class EFDbContext : DbContext
{      
       public DbSet<Person> People { get; set; }
       public DbSet<Employee> Employees { get; set; }
       public DbSet<FrDetail> FrDetails { get; set; }    
} 

public ViewResult List()
{
    EFDbContext context = new EFDbContext();
    IQueryable<FrDetail> frDetails = context.FrDetails.Include(x => x.People);
    return View(frDetails);
}

//The view

@model IQueryable<FrDetail>   
@foreach (var p in Model)
    Html.RenderPartial("FunctionRequestSummary", p);
}

//Partial View FunctionRequestSummary

@model FrDetail
@Model.People.Count()//IT'S ALWAYS ZERO
//@Model.People//NULL
@Model.People.Where(x=>x.PersonID==Model.RequestorPersonID).FirstOrDefault().FirstName

问题出现在计数始终为 0 的最后一行。我尝试过切换

ProxyCreationEnabled = 假；和 LazyLoadingEnabled = false;

这也没有帮助。我错过了什么吗？

Answer 1

这就是你想要的吗？

public abstract class Person
{
    [Key]     
    public int PersonID { get; set; }         
    public string FirstName { get; set; }      
} 
public class Employee : Person
{
    public string Department { get; set; }
}
public class FrDetail
{
    [Key]
    public int FrID { get; set; }      
    public virtual Person RequestorPerson { get; set; }
}
public class EFDbContext : DbContext
{      
       public DbSet<Person> People { get; set; }
       public DbSet<Employee> Employees { get; set; }
       public DbSet<FrDetail> FrDetails { get; set; }    
} 

public ViewResult List()
{
    EFDbContext context = new EFDbContext();
    IQueryable<FrDetail> frDetails = context.FrDetails;
    return View(frDetails);
}

//The view

@model IQueryable<FrDetail>   
@foreach (var p in Model)
{
    Html.RenderPartial("FunctionRequestSummary", p);
}

//Partial View FunctionRequestSummary

@model FrDetail
@Model.RequestorPerson.FirstName