Entity Framework: Self-join error

Question

I have the following class:

public class Application
{
    public int Id { get; set; }

    /* Other properties */

    public int LegacyId { get; set; }
    public int LegacyParentId { get; set; }

    public int? ApplicationSupersessionId { get; set; }
    public virtual ICollection<Application> ApplicationSupersessions { get; set; }

    public Application()
    {
        ApplicationSupersessions = new List<Application>();
    }
}

Where ApplicationSupersessions is an optional self-joined entity. I have data already added to my Applications table and I'm trying to adjust the data, which currently looks like this:

But I need Applications 5413 and 5414 to have an ApplicationSupersessionId of 5415 as that is what it looks like in our Legacy system, hence why I have added the 2 Legacy columns

So I've tried the following:

var applications = CatalogueContext.Applications.ToList();

foreach (var application in applications)
{
    var legacyChildren = applications.Where(x => 
        x.LegacyParentId == application.LegacyId).ToList();

    if(legacyChildren.Any())
    {
        foreach(var child in legacyChildren)
        {
            application.ApplicationSupersessions.Add(child);
        }

       CatalogueContext.Entry(application).State = EntityState.Modified;
    }
}

CatalogueContext.SaveChanges();

But I get the following error on the line CatalogueContext.Entry(application).State = EntityState.Modified;:

Answer 1

I managed to solve this. I had the relationship set up wrong in my Configuration.

I had this:

HasOptional(x => x.ApplicationSupersessions)
    .WithMany()
    .HasForeignKey(x => x.ApplicationSupersessionId)
    .WillCascadeOnDelete(false);

When it should have been this:

HasMany(x => x.ApplicationSupersessions)
    .WithOptional()
    .HasForeignKey(x => x.ApplicationSupersessionId)
    .WillCascadeOnDelete(false);

I'm not sure what the difference is and whether or not its an EF bug?