使用实体框架代码优先方法，如何创建一个具有相关实体列表作为子属性的实体？

Question

SOLVED!!!

Thanks to comments made by Gert below, I was able to solve. I simply needed to attach my Product entities to the same context as the Order entity before saving the order:

public int Create(Order entity)
        {
            var order = entity;

            foreach (var product in order.Products)
            {
                db.Products.Attach(product);
            }

            db.Orders.Add(order);
            db.SaveChanges();

            return order.Id;
        }

Original Post

Thanks for looking. Here is my use case:

On an ecommerce application, I need to create an Order . The Order has one or many Product entities as one of its properties. Here are my two domain models:

Order

 [Table("Order")]
    public class Order
    {
        [Required(ErrorMessage = "Please enter a description.")]
        public string Description { get; set; }

        [Required(ErrorMessage = "Please enter a trackingnumber.")]
        public string TrackingNumber { get; set; }

        [Key]
        public int Id { get; set; }

        [Required(ErrorMessage = "Please enter an isactive.")]
        public bool IsActive { get; set; }

        public int UserId { get; set; }

        public virtual User User { get; set; }

        public int OrderStatusTypeId { get; set; }

        public virtual OrderStatusType OrderStatusType { get; set; }

        private ICollection<Product> _products;
        public virtual ICollection<Product> Products
        {
            get { return _products ?? (_products = new Collection<Product>()); }
            set { _products = value; }
        }
    }

Product

[Table("Product")]
    public class Product
    {
        [Required(ErrorMessage = "Please enter a description.")]
        public string Description { get; set; }

        [Key]
        public int Id { get; set; }
        [Required(ErrorMessage = "Please enter a name.")]
        public string Name { get; set; }


        private ICollection<Order> _orders;
        public virtual ICollection<Order> Orders
        {
            get { return _orders ?? (_orders = new Collection<Order>()); }
            set { _orders = value; }
        }

        private ICollection<DeviceModel> _devicemodels;
        public virtual ICollection<DeviceModel> DeviceModels
        {
            get { return _devicemodels ?? (_devicemodels = new Collection<DeviceModel>()); }
            set { _devicemodels = value; }
        }
    }

Here is a look at a post object that the user has created:

{
  "Description": "Test description",
  "TrackingNumber": "12345",
  "Id": 1,
  "IsActive": true,
  "UserId": 0,
  "User": {
    "Email": "john@gmail.com",
    "FirstName": "John",
    "Id": 1,
    "LastName": "Doe"
  },
  "OrderStatusTypeId": 0,
  "OrderStatusType": {
    "Description": "The order is in processing.",
    "Id": 1,
    "Title": "Processing"
  },
  "Products": [{"Description":"Test product","Id":1,"Name":"Product A","DeviceModels":[]},{"Description":"Test","Id":2,"Name":"Product B","DeviceModels":[]}]
}

Expected Behavior

When I POST this Order object to the server, I would have expected that a new order is created and the products belonging to that order would simply be referenced.

Encountered Behavior

Each time I place an order, the related products are added a new products to the product table. So, rather than having a few products that are referenced by several orders, I have several products with 1-to-1 relationship with the orders.

Here is what my Products table ends up looking like (note the repeated products):

UPDATE

The Code First Approach DOES create a ProductOrders conjunction table for me, and it even adds the order and product ids to that table:

So why does it also add the products as new entities in the Product table rather than simply referencing the keys I pass to it?

Thanks in advance.

UPDATE #1:

Here is my repository class for creating orders:

  public class OrderRepository : IRepository<Order, int>
    {
        private readonly ApplicationDbContext db;

        public OrderRepository(ApplicationDbContext dbContext)
        {
            db = dbContext;
        }

        /// <summary>
        ///     Creates and saves a new 'Order' entity.
        /// </summary>
        /// <param name="entity">The Order to save.</param>
        /// <returns>The id (int) of the newly created Order.</returns>
        public int Create(Order entity)
        {
            var order = entity;
            db.Orders.Add(order);
            db.SaveChanges();

            return order.Id;
        }

        }
    }

Answer 1

You will need to define the mappings for your collections. Here is an example using the fluent mapping interface.

public class OrderMapping:  EntityTypeConfiguration<Order>
{
       public OrderMapping()
      {
         HasMany(o => o.Products).WithMany(p => p.Orders).Map(m =>
            {
                m.MapLeftKey("OrderId");
                m.MapRightKey("ProductId");
                m.ToTable("Order_Products");
            });
      }          
}

This will create a link table between Orders and Products.