EntityFramework 6关系映射到许多项目

Question

I feel like my mapping should be setup correctly, but when I retrieve an item from the db context, it comes with none of the "mapped" items related to it.

The mapping I'm going for is this:

Top level item is an "Event".

An event has many "TimeSlot" associated with it.

A TimeSlot has many strings associated with it.

public class MyEvent
{
    private ICollection<TimeSlot> mTimeSlots;

    public virtual ICollection<TimeSlot> TimeSlots
    {
       get{return mTimeSlots ?? (mTimeSlots = new Collection<TimeSlot>());}
       set{mTimeSlots = value;}
    }

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

And my TimeSlot looks like:

public class TimeSlot
{
    private ICollection<string> mItems;

    public virtual ICollection<string> Items
    {
        get { return mItems ?? (mItems = new Collection<string>()); }
        set { mItems = value; }
    }

    [Key]
    public virtual int Id { get; set; }

    public virtual string Label { get; set; }
}

My DbContext looks like:

public class MyEventsDataContext : DbContext
{
    public MyEventsDataContext()
        : base("MyEventsDatabase")
    {
        // Do nothing.
    }

    public DbSet<MyEvent> MyEvents { get; set; }
    public DbSet<TimeSlot> TimeSlots { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<MyEvent>()
            .HasMany<TimeSlot>(e => e.TimeSlots);
    }
}

I'm migrating some default data for testing purposes like this:

    protected override void Seed(MyEventsDataContext context)
    {
        //  This method will be called after migrating to the latest version.

        var timeSlot1 = new TimeSlot {Label = "Slot 1"};
        timeSlot1.Items.Add("Do stuff 1");
        timeSlot1.Items.Add("Do stuff 2");
        timeSlot1.Items.Add("Do stuff 3");

        var timeSlot2 = new TimeSlot {Label = "Slot 2"};
        timeSlot2.Items.Add("Do stuff 1");
        timeSlot2.Items.Add("Do stuff 2");
        timeSlot2.Items.Add("Do stuff 3");

        var timeSlot3 = new TimeSlot {Label = "Slot 3"};
        timeSlot3.Items.Add("Do stuff 1");
        timeSlot3.Items.Add("Do stuff 2");
        timeSlot3.Items.Add("Do stuff 3");

        context.TimeSlots.AddOrUpdate(new[] {timeSlot1, timeSlot2, timeSlot3});

        var event1 = new MyEvent
        {
            Address = "123 Street Ln",
            CampaignId = "abc123",
            City = "City",
            CreatedDate = DateTime.Now,
            EventDate = DateTime.Now,
            EventType = "TradeShow",
            Name = "Show Name",
            ProductInterest = "MyArm",
            State = "State",
            Zipcode = "12345",
            TimeSlots = new Collection<TimeSlot> {timeSlot1, timeSlot2, timeSlot3}
        };
        context.MyEvents.AddOrUpdate(event1);

        var event2 = new MyEvent
        {
            Address = "321 Street Ln",
            CampaignId = "123abc",
            City = "City",
            CreatedDate = DateTime.Now,
            EventDate = DateTime.Now,
            EventType = "Conference",
            Name = "Show Name",
            ProductInterest = "MyArm",
            State = "State",
            Zipcode = "54321",
            TimeSlots = new Collection<TimeSlot> {timeSlot1, timeSlot2, timeSlot3}
        };
        context.MyEvents.AddOrUpdate(event2);
    }

And in my Controller, when I go to retrieve an event from the DbContext it has no attached TimeSlots to it (it's empty).

MyEvent show = mDb.MyEvents.Find(id);

Any advice here would be much appreciated. I am probably just not setting up the mapping correctly.

Answer 1

You have to turn on the LazyLoading

public MyEventsDataContext()
    : base("MyEventsDatabase")
{
    this.Configuration.LazyLoadingEnabled = true;
}

or you should include the property.

mDb.MyEvents.Include("TimeSlots").Find(id)