Unable to cast code first

Question

Having this class that represents model

public class User : IHaveId
{
    public User()
    {
        Operations = new Collection<Operation>();
    }
    public int Id { get; set; }
    public string UserName { get; set; }
    public string CardNumber { get; set; }
    public string Pin { get; set; }
    public double Balance { get; set; }
    public bool Blocked { get; set; }
    public ICollection<Operation> Operations { get; set; }


}

and this seed method in my own Initializer:

    protected override void Seed(BankContext context)
    {
        var users = MockData.GetUsers();
        foreach (var user in users)
        {
            user.Operations.Add(
                    new Operation
                    {
                        OperationType = OperationType.Balance,
                        PerformTime = DateTime.Now.AddDays(-10)
                    }
            );

            user.Operations.Add(
                    new Operation
                    {
                        OperationType = OperationType.GetMoney,
                        PerformTime = DateTime.Now.AddDays(-5),
                        AdditionInformation = "800"
                    }
            );

            context.Users.Add(user);
        }
        base.Seed(context);
    }

Having exception at Add stage saying: Unable cast Collection<Operation> to Operation. Can someone explain why this happening?

Do i need to specify anything special in onModelCreating for this case?

Answer 1

Since User.Operations is supposed to be a collection property (and not a reference property), you need to use HasMany:

modelBuilder.Entity<User>()
    .HasMany(a => a.Operations)
    .WithOptional()
    .WillCascadeOnDelete(true);

Originally, you were telling EF that User.Operations is a reference property, which causes an error when you try to assign a collection to it.

Answer 2

Okey, i found the issue, As i thought there was a reason outside of the posted code. In my BankContext class i have

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {

        modelBuilder.Entity<User>()
            .HasOptional(a => a.Operations)
            .WithOptionalDependent()
            .WillCascadeOnDelete(true);
    }

That some how influent on this. Can anyone explain how that influent?