Question

I’m trying to update a model, but get the error “The operation failed: The relationship could not be changed because one or more of the foreign-key properties is non-nullable. When a change is made to a relationship, the related foreign-key property is set to a null value. If the foreign-key does not support null values, a new relationship must be defined, the foreign-key property must be assigned another non-null value, or the unrelated object must be deleted.”

From what I understand from The relationship could not be changed because one or more of the foreign-key properties is non-nullable the problem might be with how Entity Framework handles my virtual ICollection

However I’m not really sure how to implement the solution when using scaffolded repository pattern. Do I have to edit the Save()-method ParentObjectRepository-class?

Actually I really think that there must be some way to make EF understand this. I can’t see how the EF-team was thinking “Probably noone is using a collection of objects with a foreign key constraint, lets not support that”.

Update
Added code

[HttpPost]
public ActionResult Edit(int id, FormCollection formCollection)
{
    var eventRepository = new MagnetEventRepository();
    var original = eventRepository.Find(id);
    UpdateModel(original);
    eventRepository.Save();
    return RedirectToAction("Details", "Home", new { slug = original.Slug });
}

public void Save()
{
    context.SaveChanges();
}

More code:

public class MagnetEvent
{
    public virtual int Id { get; set; }

    [Required]
    public virtual string Name { get; set; }

    [Required]
    [DisplayFormat(DataFormatString = "{0:yyyy-MM-dd HH:mm}")]
    [DataType(DataType.DateTime)]
    public virtual DateTime? StartDate { get; set; }

    public virtual string Description { get; set; }

    [StringLength(100)]
    public virtual string Slug { get; set; }

    public virtual int MaximumCapacity { get; set; }

    [DataType(DataType.Currency)]
    public virtual int TicketPrice { get; set; }

    public virtual int LocationId { get; set; }
    public virtual Location Location { get; set; }

    public virtual Collection<Ticket> Tickets { get; set; }

    public virtual Collection<AttendeeInformationField> CaptureAttendeeInformationFields { get; set; }

    public virtual int CustomerId { get; set; }

    [Required]
    public virtual CUSTOMER Customer { get; set; }
}

The Save()-method is from MagnetEventRepository, which is scaffolded from the above class.

Another update
I successfully removed the error by changing MagnetEventId in AttendeeInformationField to nullable int. When examining the database I can see exactly what’s wrong.

Let’s say I have a single AttendeeInformationField with the value “E-mail”. When I edit my MagnetEvent, the AttendeeInformationField updates the MagnetEventId to null and then adds a new post with the correct MagnetEventId and Value.

I’d very much prefer if the posts in AttendeeInformationField were updated instead.

Answer 1

I found a solution to my problem. It seems to be a bug (?) in ASP.NET MVC when it comes to UpdateModel and a model containing an ICollection.

The solution is to override the default behaviour, as described in this blog post: http://www.codetuning.net/blog/post/Binding-Model-Graphs-with-ASPNETMVC.aspx

Update
I found a solution! The above only worked when updating existing items in the collection. To solve this, I have to manually check and add new AttendeeInformationFields. Like this:

[HttpPost]
public ActionResult Edit(int id, MagnetEvent magnetEvent)
{
    var eventRepository = new MagnetEventRepository();
    var original = eventRepository.Find(id);
    UpdateModel(original);
    foreach (var attendeeInformationField in magnetEvent.CaptureAttendeeInformationFields)
    {
        var attendeeInformationFieldId = attendeeInformationField.Id;
        if (original.CaptureAttendeeInformationFields.AsQueryable().Where(ai => ai.Id == attendeeInformationFieldId).Count() == 0)
        {
            original.CaptureAttendeeInformationFields.Add(attendeeInformationField);
        }
    }
    eventRepository.Save();
}

Together with the modified DefaultModelBinder, this actually works with both editing and adding. For now I haven’t tried deleting.

Still, I hope there is a simpler way to do this. Seems like a lot of coding to do a very basic task.