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实体框架自动填充错误的实体

wcf entity-framework asp.net-mvc

Sanjeewa severino · 技术社区 · 8 年前

我正在开发带有ASP.NET MVC、实体框架和WCF的音乐商店示例应用程序。

这是一个分层应用程序,它为实体提供了一个公共层。

我写了一个种子方法,它可以很好地工作,但是当我试图添加一个 Album 致 Cart ,另一个副本 专辑 也添加到 专辑 表加副本 Artists 也添加了。当我在填充 购物车 对象。我添加了这个语句,因为当我创建视图时,它为 item.Album.Title 进入

这是我的代码:

public static void AddToCart(Album album, string ShoppingCartID)
{
            using (MusicStoreEntities db = new MusicStoreEntities())
            {
                // Get the matching cart and album instances
                var cartItem = db.Carts.SingleOrDefault(
                    c => c.CartId == ShoppingCartID
                         && c.AlbumId == album.AlbumId);

                if (cartItem == null)
                {
                    // Create a new cart item if no cart item exists
                    cartItem = new Cart
                    {
                        AlbumId = album.AlbumId,
                        CartId = ShoppingCartID,
                        Count = 1,
                        DateCreated = DateTime.Now,
                        Album = album
                    };

                    db.Carts.Add(cartItem);
                }
                else
                {
                    // If the item does exist in the cart, then add one to the quantity
                    cartItem.Count++;
                }

                // Save changes
                db.SaveChanges();
            }
}

模型类:

namespace MusicStore.Core
{
    [Serializable]
    [DataContract]
    //[Bind(Exclude = "AlbumId")]
    public class Album
    {
        [DataMember]
        [ScaffoldColumn(false)]
        public int AlbumId { get; set; }

        [DataMember]
        [DisplayName("Genre")]
        public int GenreId { get; set; }

        [DataMember]
        [DisplayName("Artist")]
        public int ArtistId { get; set; }

        [DataMember]
        [Required(ErrorMessage = "An Album Title is required")]
        [StringLength(160)]
        public string Title { get; set; }

        [DataMember]
        [Required(ErrorMessage = "Price is required")]
        [Range(0.01, 100.00, ErrorMessage = "Price must be between 0.01 and 100.00")]
        public decimal Price { get; set; }

        [DataMember]
        [DisplayName("Album Art URL")]
        [StringLength(1024)]
        public string AlbumArtUrl { get; set; }

        [DataMember]
        public virtual Genre Genre { get; set; }

        [DataMember]
        public virtual Artist Artist { get; set; }
        public virtual List<OrderDetail> OrderDetails { get; set; }
    }
}

namespace MusicStore.Core
{
    [Serializable]
    [DataContract]
    public class Cart
    {
        [Key]
        [DataMember]
        public int RecordId { get; set; }
        [DataMember]
        public string CartId { get; set; }
        [DataMember]
        public int AlbumId { get; set; }
        [DataMember]
        public int Count { get; set; }
        [DataMember]
        public System.DateTime DateCreated { get; set; }
        [DataMember]
        public virtual Album Album { get; set; }
    }
}

种子方法:

namespace MusicStore.Data
{
    internal class CommonDBInitializer : CreateDatabaseIfNotExists<MusicStoreEntities>
    {
        protected override void Seed(MusicStoreEntities context)
        {
            var genres1 = new List<Genre>
            {
                new Genre
                {
                    Name = "Rock",
                    Description = "Rock",
                    Albums = new List<Album>()
                },
                new Genre
                {
                    Name = "Jazz",
                    Description = "Jazz",
                    Albums = new List<Album>()
                },
                new Genre
                {
                    Name = "Metal",
                    Description = "Metal",
                    Albums = new List<Album>()
                },
                new Genre
                {
                    Name = "Alternative",
                    Description = "Alternative",
                    Albums = new List<Album>()
                },
                new Genre
                {
                    Name = "Disco",
                    Description = "Disco",
                    Albums = new List<Album>()
                },
                new Genre
                {
                    Name = "Blues",
                    Description = "Blues",
                    Albums = new List<Album>()
                },
                new Genre
                {
                    Name = "Latin",
                    Description = "Latin",
                    Albums = new List<Album>()
                },
                new Genre
                {
                    Name = "Reggae",
                    Description = "Reggae",
                    Albums = new List<Album>()
                },
                new Genre
                {
                    Name = "Pop",
                    Description = "Pop",
                    Albums = new List<Album>()
                },
                new Genre
                {
                    Name = "Classical",
                    Description = "Classical",
                    Albums = new List<Album>()
                },
            };
            genres1.ForEach(d => context.Genres.Add(d));
            context.SaveChanges();

            var artist1 = new List<Artist>
            {
                new Artist
                {
                    Name = "Aaron Copland & London Symphony Orchestra",

                },
                 new Artist
                {
                    Name = "Barry Wordsworth & BBC Concert Orchestra",

                },

            };

            artist1.ForEach(d => context.Artists.Add(d));
            context.SaveChanges();

            var album1 = new List<Album>
            {
                new Album { Title = "The Best Of Men At Work",  Price = 8.99M,  AlbumArtUrl = "/Content/Images/placeholder.gif",Genre = genres1.FirstOrDefault(d => d.GenreId == 1), Artist  = artist1.FirstOrDefault(d => d.ArtistId == 1) },
               new Album { Title = "A Copland Celebration, Vol. I",  Price = 8.99M, AlbumArtUrl = "/Content/Images/placeholder.gif",Genre = genres1.FirstOrDefault(d => d.GenreId == 2),Artist  = artist1.FirstOrDefault(d => d.ArtistId == 2) },

            };

            album1.ForEach(s => context.Albums.Add(s));

            context.SaveChanges();

        }
    }

控制器:

namespace MusicStore.Web.Controllers
{
    public class ShoppingCartController : Controller
    {
        MusicShoppingCartMgr.Cart serviceref1 = new MusicShoppingCartMgr.Cart();
        MusicShoppingCartMgr.iShoppingCart servicemethodref1 = new iShoppingCartClient();
        //
        // GET: /ShoppingCart/
        public ActionResult Index()
        {
            var cart = ShoppingCart.GetCart(this.HttpContext);

            // Set up our ViewModel
            var viewModel = new ShoppingCartViewModel
            {
                CartItems = cart.GetCartItems(cart.ShoppingCartId),
                CartTotal = cart.GetTotal(cart.ShoppingCartId)
            };

            // Return the view
            return View(viewModel);
        }
        //
        // GET: /Store/AddToCart/5

        public ActionResult AddToCart(int id)
        {
            var addedAlbum = servicemethodref1.GetAlbum(id);

            // Add it to the shopping cart
            var cart = ShoppingCart.GetCart(this.HttpContext);

            cart.AddToCart(addedAlbum, cart.ShoppingCartId);

            // Go back to the main store page for more shopping
            return RedirectToAction("Index");
        }

    }
}

视图:

@model MusicStore.Web.ViewModels.ShoppingCartViewModel
@{
    ViewBag.Title = "Shopping Cart";
}
<script src="/Scripts/jquery-1.10.2.min.js" type="text/javascript"></script>

<h3>
    <em>Review</em> your cart:
</h3>
<p class="button">
    @Html.ActionLink("Checkout >>", "AddressAndPayment", "Checkout")
</p>
<div id="update-message">
</div>
<table>
    <tr>
        <th>
            Album Name
        </th>
        <th>
            Price (each)
        </th>
        <th>
            Quantity
        </th>
        <th></th>
    </tr>
    @foreach (var item in Model.CartItems)
    {
        <tr id="row-@item.RecordId">
            <td>
                @Html.ActionLink(item.Album.Title, "Details", "Store", new { id = item.AlbumId }, null)
            </td>
            <td>
                @item.Album.Price
            </td>
            <td id="item-count-@item.RecordId">
                @item.Count
            </td>
            <td>
                <a href="#" class="RemoveLink" data-id="@item.RecordId">Remove from cart</a>
            </td>
        </tr>
    }
    <tr>
        <td>
            Total
        </td>
        <td></td>
        <td></td>
        <td id="cart-total">
            @Model.CartTotal
        </td>
    </tr>
</table>

问题是 :为什么它会以这种不寻常的方式自动填充,以及如何修复它?

1 回复 | 直到 8 年前

Sanjeewa severino 8 年前

你有复制品是因为 AddToCart 方法,您实例化了一个新的上下文 MusicStoreEntities .上下文不知道 Album 你通过的实体 album 参数。

因此,当您执行此代码时:

cartItem = new Cart
{
    // [...]
    Album = album
};

然后打电话来 db.Carts.Add(cartItem); ,的 cartItem 将打开 Added 州。EF还将检查 购物车项目 对象图并发现 专辑 未被新上下文跟踪(请记住,此实例来自方法的参数),然后默认情况下,它还会将该实体置于 补充 州。英孚也会这么做的 专辑 对象图形,您将打开该相册的艺术家 补充 也请说明。打电话时 db.SaveChanges(); ,每个实体 补充 状态将被视为在数据库中生成一个新的插入,所以这就是为什么要进行复制。

要解决此问题,您可以致电 db.Attach(album) 并让上下文关注如下实体:

using (MusicStoreEntities db = new MusicStoreEntities())
{
     db.Albums.Attach(album);

    // [...]
}

或使用 专辑 例如,您可以只设置外键属性 AlbumId 然后摆脱 专辑 财产转让。因此,在创建新购物车项目时,您只需要这样做:

cartItem = new Cart
{
    AlbumId = album.AlbumId,
    CartId = ShoppingCartID,
    Count = 1,
    DateCreated = DateTime.Now
};