EF6 可选 1:1 包括不工作

Question

Trying to set up basic EF6 Optional 1:1. Extremely frustrating. I have read lots and lost of posts.

I have two entities, Guests and Seats, each one can exist on their own, a seat does not need a guest and a guest does not need a seat.

Guest Model:

        public int ID { get; set; }

        public int? SeatID { get; set; }

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

        //Link to Seat
        public Seat Seat { get; set; }

Seat Model:

        public int ID { get; set; }

        public int? GuestID { get; set; }

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

        public bool Occupied { get { return (GuestID == null ? true : false); } }

        //Link to Guest
        public Guest Guest{ get; set; }

I had lots of problems just getting to this point. I had to add this to my model creation for the relationship to work:

       modelBuilder.Entity<Seat>()
            .HasOptional(g => g.Guest)
            .WithOptionalDependent(s => s.Seat);

Now my application is working however when I try and load related data with the include method it just comes up blank, nothing there.

var seats = db.Seats.Include(s => s.Guest);
            return View(seats.ToList());

On my view I use

@Html.DisplayFor(modelItem => item.Guest.FirstName)

I want to know how to make the include statement work, preferably without lazy loading (or even with if i have to). Also, I do not want to have a SeatAssignment table, I considered going down this road.

I could use a Viewmodel for this to work but i dont understand why the 1:1 optional is not loading the related data.

As requested, here is the generated schema...definitely something odd going on here. As a side note i can make it work with a viewmodel, but i dont want to.

Answer 1

1-0..1 relationship configuration is different from the way that you want.

1. 1-0..1 relation ship between X and Y means that XId is primary key in X and also XId is also primary key in Y and also foreign key
2. What you are requesting is a mn relationship with m=1 and n=1, so the configuration should be different.

Based on the above mentioned rules, your code should be as follows

Guest class

public class Guest
{
    public int ID { get; set; }
    [Required]
    public string FirstName { get; set; }

    public IList<Seat> Seats { get; set; }
}

Seat class

public class Seat
{
    public int ID { get; set; }
    [Required]
    public string SeatNumber{ get; set; }

    public IList<Guest> Guests { get; set; }
}

Join table

public GuestSeat
{
     public int GuestID{get;set;}
     public int SeatID{get;set;}

     public DateTime ReservedDate{get;set;}
     // other fields goes here
}

Configuration

modelBuilder.Entity<GuestSeat>()
            .HasKey(gs => new {gs.GuestID,gs.SeatID})
            .ToTable("GuestSeats");
modelBuilder.Entity<GuestSeat>()
            .HasRequired(g=>g.Guest)
            .WithMany(g=>g.Seats)
            .HasForeignKey(gs =>gs.GuestID)
            .DeleteOnCascade(false);
modelBuilder.Entity<GuestSeat>()
            .HasRequired(s=>s.Seat)
            .WithMany(s=>s.Guests)
            .HasForeignKey(gs =>gs.SeatID)
            .DeleteOnCascade(false);

This solution provide the following

1. As a Guest,On today's event, I can reserve seat A, and tomorrow's event, I can reserve seat B.
2. Seat A can be occupied by Guest X and tomorrow by Guest Y
3. To ensure that the seat can be occupied by one person on a given date, you can create a unique index on the SeatID and ReservedDate .

Hope this will help you

Answer 2

You have to construct your models as shown below.

public class Guest
{
        public int GuestId { get; set; }

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

        //Link to Seat
        public virtual Seat Seat { get; set; }
}

public class Seat
{
        public int SeatId { get; set; }

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

        public bool Occupied { get { return (GuestID == null ? true : false); }}

        //Link to Guest
        public virtual Guest Guest{ get; set; }
}

Fluent API mapping :

  modelBuilder.Entity<Seat>()
            .HasOptional(g => g.Guest)
            .WithOptionalDependent(s => s.Seat);

Then :

var seats = db.Seats.Include(s => s.Guest).ToList();