双外键：C＃中的多重性错误

Question

I have a Entity framework set of Auctions. Every auctions has a 2 foreign key to the User DB object. [the creator (required) and the current winner (optional)]

    ....

public class UserDB {

    [Key]
    public int Id { get; set; }
    public virtual ICollection<AuctionDB> WinnerOfAucts { get; set; }
    public virtual ICollection<AuctionDB> SellerOfAucts { get; set; }

... } public class AuctionDB {

    [Key]
    public int Id { get; set; }
    public virtual UserDB WinnerUser { get; set; }
    public virtual int WinnerUserId { get; set; }
    public virtual int SellerId { get; set; }  
    public virtual UserDB Seller { get; set; }

... }

There is the code of the foreign keys:

modelBuilder.Entity<AuctionDB>().HasRequired(a => a.Seller).WithMany(u => u.SellerOfAucts).HasForeignKey(a => a.SellerId).WillCascadeOnDelete(true);
            modelBuilder.Entity<AuctionDB>().HasOptional(a => a.WinnerUser).WithMany(u => u.WinnerOfAucts).HasForeignKey(a => a.WinnerUserId).WillCascadeOnDelete(false);

The project keeps saying this error message: SetUp: System.Data.Entity.ModelCongifuration.ModelValidationException : One or more validation errors were detected during model generation:

AuctionSite.AuctionDB_WinnerUser: : Multitplicity conflicts with the referential constraint in Role 'AuctionDB_WinnerUser_Target' in relationship 'AuctionDB_WinnerUser'. Because all of the properties in the Dependent Role are non-nullable, multiplicity of the Principal Role must be '1'.

The problem is on the db.Database.Delete() method:

            if (connectionString == null) throw new ArgumentNullException();
        using (var db = new AuctionContext(connectionString))
        {
            try
            {
                db.Database.Delete();
                db.Database.Create();
            }
            catch (SqlException)
            {
            throw new UnavailableDbException();}

Any help? Thank you

Answer 1

Initialise your collection

public UserDB()
{
WinnerOfAucts = new List<AuctionDB>();
SellerOfAucts = new List<AuctionDB>();
}