EF核心-包含然后包含接口

Question

I am trying to load related data using .Include().ThenInclude() . I am using inheritance and my classes deriving from the base class TicketEntry can implement an interface IApprovable :

public class Ticket
{
    [Key]
    public int Id { get; set; }

    [Required]
    public string Title { get; set; }

    public ICollection<TicketEntry> TicketEntries { get; set; }
}

public abstract class TicketEntry
{
    [Key]
    public int Id { get; set; }

    [Required]
    [DatabaseGenerated(DatabaseGeneratedOption.Computed)]
    public DateTime CreationDate { get; set; }

    [Required]
    public string UserId { get; set; }
    [ForeignKey("UserId")]
    public ApplicationUser User { get; set; }

    public int TicketId { get; set; }
    [ForeignKey("TicketId")]
    public Ticket Ticket { get; set; }
}

public class Common : TicketEntry
{
    [Required]
    public string Description { get; set; }
}

public class CostEstimate : TicketEntry, IApprovable
{
    [Required]
    [Column(TypeName = "money")]
    public decimal Estimate { get; set; }

    public Boolean? Approved { get; set; }

    public string ApprovingUserId { get; set; }
    [ForeignKey("ApprovingUserId")]
    public ApplicationUser ApprovingUser { get; set; }
}

Now I want to get a Ticket with all it's TicketEntries and their User and the ApprovingUser for all the TicketEntries implementing the Interface IApprovable .

I tried doing this:

_context.Ticket
    .Include(t => t.TicketEntries)
        .ThenInclude(te => te.User)
    .Include(t => t.TicketEntries as ICollection<IApprovable>)
        .ThenInclude(ia => ia.ApprovingUser)

Which doesn't work since it's not a pure property expression.

I tried to look up similar cases but couldn't find any. Am I missing something or is that simply not possible and I'm trying to do something you normally should not do?

Even if one shouldn't, how would you accomplish this?

Answer 1

It's not possible to include derived in EntityFramework Core 2.0 or older.

There is an GitHub Issue Query: Support Include/ThenInclude for navigation on derived type requesting this feature, which was added to EntityFramework Core 2.1-preview1.

As per 2.1 documentation and What's new in 2.1 you can use it via one of the following syntax:

var option1 = context.People.Include(p => ((Student)p).School);
var option2 = context.People.Include(p => (p as Student).School);
var option3 = context.People.Include("School");

Update: build 2018 announcement & production ready

https://blogs.msdn.microsoft.com/dotnet/2018/05/07/announcing-entity-framework-core-2-1-rc-1/

Today, we are excited to announce that the first release candidate of EF Core 2.1 is available, alongside .NET Core 2.1 RC 1 and ASP.NET Core 2.1 RC 1, for broad testing, and now also for production use !