我正在使用ASP.NET MVC，实体框架和WCF开发音乐商店示例应用程序。
这是一个分层应用程序，它具有实体的公共层。
我编写了一个可行的种子方法，但是当我尝试向Album添加Cart时，另一个重复的Album也会添加到Album表格加上重复Artists也会被添加。当我在填充Cart对象时添加Album = album语句时会发生这种情况。我添加了这个语句，因为当我创建视图时，它会为item.Album.Title条目
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");
}
}
}
查看：
@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：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？
答案 0 :(得分：1)
您有重复，因为在您的AddToCart方法中，您实例化了一个新的上下文MusicStoreEntities。该上下文对您通过Album参数传递的album实体一无所知。
所以当你做这个代码时：
cartItem = new Cart
{
// [...]
Album = album
};
并且呼叫db.Carts.Add(cartItem);，cartItem将处于Added状态。 EF还会检查cartItem对象图，发现新上下文没有跟踪album（请记住此实例来自您的方法参数），然后默认情况下它也会将Added州的实体。 EF会对album对象图执行相同的操作，您也会在Added状态下获得该相册的艺术家。在调用db.SaveChanges();时，具有Added状态的每个实体都将被视为生成新的数据库插入，这就是您复制的原因。
要解决此问题，您可以致电db.Attach(album)并让上下文照顾下面的实体：
using (MusicStoreEntities db = new MusicStoreEntities())
{
db.Albums.Attach(album);
// [...]
}
或者使用album实例，您只需设置外键属性AlbumId并摆脱Album属性赋值。因此，在创建新购物车项目时，您只需拥有此功能：
cartItem = new Cart
{
AlbumId = album.AlbumId,
CartId = ShoppingCartID,
Count = 1,
DateCreated = DateTime.Now
};