英文:
Entity Framework how to derive from a non existent class
问题
请见谅，我不是开发人员，所以如果我没有使用正确的术语，我道歉。我正在使用代码优先的 EF 构建一个非常简单的库存管理应用程序。我有一个类，它是我的产品（为简洁起见进行了简化）：
public class Product()
{
this.Shops = new HashSet<Shop>();
}
public int Id { get; set; }
public string ProductDescription { get; set; }
public virtual ICollection<Shop> Shops { get; set; }
以及我的 Shop 类：
public Shop()
{
this.Products = new HashSet<Product>();
}
public int Id { get; set; }
public string ShopName { get; set; }
public virtual ICollection<Product> Products { get; set; }
并不是所有产品都在所有商店都可用，上述代码已经可以正常工作。EF 已经创建了映射表 ProductShop，我可以在任何商店中提供任何我想要的产品。
我的问题是如何处理每个商店可用的每个项目的数量。最初，我认为可以从 ProductShop 实体派生一个新类，带有类似这样的数量字段：
public class ShopStockQuantities : ProductShop
{
public int Qty { get; set; }
}
但我没有一个物理类来派生。如果我添加了这个类，EF 会不会因为该表已经存在而出错？我相信这个问题以前已经遇到过，所以为了节省我尝试的时间（因为我不太擅长这个），我想从这些专家中寻求建议。任何建议都将不胜感激。
英文:
Please bear with me, I am not a developer, so I apologise if I don't use the correct terminology, but I am building a very simple stock management app using code first EF. I have one class which is my Products (simplified for brevity):
public class Product()
{
this.Shops = new HashSet<Shop>
}
public int Id { get; set; }
public string ProductDescription { get; set; }
public virtual ICollection<Shop> Shops { get; set; }
And my Shop class:
public Shop()
{
this.Products = new HashSet<Product>();
}
public int Id { get; set; }
public string ShopName { get; set; }
public virtual ICollection<Product> Products { get; set; }
Not all products will be available at all shops, and the above works perfectly. EF has created the mapping table ProductShop and I can make whatever products I like available at any of the shops.
My problem is how to deal with the quantity of each item that is available at each shop. Initially I thought I could just derive a new class from the ProductShop entity with a quantity field like this:
public class ShopStockQuantities : ProductShop
{
public int Qty { get; set; }
}
but I don't have a physical class to derive from. If I add that class, will EF get in a knot as that table already exists? I am sure this issue has been encountered before, so to save me hours of experimenting (as I am not very good at this anyway) I thought I would seek advice from this Borg of experts. Any advice gratefully received.
答案1
得分: 1
根据您提供的信息，这是一个可能的类结构，基本反映了Wiktor和HH所说的内容。
public class Product
{
[Key] public int ProductId { get; set; }
public string ProductDescription { get; set; } = "Not Set";
}
public class Shop
{
[Key] public int ShopId { get; set; }
public string ShopName { get; set; } = "Not Set";
public ICollection<Stock> StockItems { get; set; } = new Collection<Stock>();
}
public class Stock
{
[Key] public int StockId { get; set; }
public int ShopId { get; set; } // 外键链接到 Shop
public int ProductId { get; set; } // 外键到 Product
public int Quantity { get; set; }
}
英文:
Based on the information you've provided, this is one possible class structure which basically reflects what Wiktor and HH are saying.
public class Product
{
[Key] public int ProductId { get; set; }
public string ProductDescription { get; set; } = "Not Set";
}
public class Shop
{
[Key] public int ShopId { get; set; }
public string ShopName { get; set; } = "Not Set";
public ICollection<Stock> StockItems { get; set; } = new Collection<Stock>();
}
public class Stock
{
[Key] public int StockId { get; set; }
public int ShopId { get; set; } // foreign key link to Shop
public int ProductId { get; set; } // foreign key to Product
public int Quantity { get; set; }
}
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