子实体不更新/添加.NET核心

public class Order
{
    public int Id { get; set; }
    public List<OrderItem> OrderItems { get; set; }
}

public class OrderItem
{
    public int Id { get; set; }
    public int OrderId { get; set; }
    public Order Order { get; set; }
}

public class ApplicationDbContext : DbContext
{
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Order>()
            .HasMany(o => o.OrderItems)
            .WithOne(oi => oi.Order)
            .HasForeignKey(oi => oi.OrderId)
            .OnDelete(DeleteBehavior.Cascade);
    }
}

var order = new Order();
var orderItem = new OrderItem { /* 初始化子实体 */ };
order.OrderItems.Add(orderItem);

using (var context = new ApplicationDbContext())
{
    context.Orders.Add(order);
    context.SaveChanges();
}