删除在多个实体上拆分的表行时出错 [英] Error deleting a table row splitted on multiple entities

问题描述

我要删除拆分为两个实体的表行。

I want to delete a table row that is split on two entities.

如果我尝试删除主实体，如果在不这样做之前会收到错误消息t使用 context.Entry（...）。Reference ..

If I try to delete the main entity, I get an error if before I don't load the related other entity using context.Entry(...).Reference..

加载相关的其他实体在我要删除整行之前傻傻地检索相关实体吗？

Is a bit silly to retrieve the related entities before, when I am going to delete the full row?

如果我继续评论上下文，则会出现以下错误.Entry（...）行

遇到无效数据。缺少必要的关系。检查
状态条目以确定约束违反的来源。

Invalid data encountered. A required relationship is missing. Examine State Entries to determine the source of the constraint violation.

我添加以下代码。

 using System.Data.Entity;
 using System.Linq;

 namespace Split
 {
   class Program
   {
     static void Main(string[] args)
     {
        using (var context = new DataContext())
        {
            var product = new Product()
            {
                Name = "my Article",
                Photo = new ProductPhoto() { PhotoUrl = "http://myfoto.jpg" }
            };

            context.Products.Add(product);
            context.SaveChanges();
        }

        using (var context = new DataContext())
        {
            var product = context.Products.First();
            //context.Entry(product).Reference(e => e.Photo).Load();
            context.Products.Remove(product);
            context.SaveChanges();
        }
     }
   }

  class Product
  {
    public virtual int Id { get; set; }
    public virtual string Name { get; set; }
    public virtual ProductPhoto Photo { get; set; }
  }

  class ProductPhoto
  {
    public virtual int ProductId { get; set; }
    public virtual string PhotoUrl { get; set; }
    public virtual Product Product { get; set; }
  }

  class DataContext : DbContext
  {
    public DataContext()
        : base("name=DefaultConnection")
    {
        Configuration.ProxyCreationEnabled = false;
        Configuration.LazyLoadingEnabled = false;
    }

    public DbSet<Product> Products { get; set; }
    public DbSet<ProductPhoto> ProductPhotos { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Product>()
            .ToTable("Products")
            .HasKey(e => e.Id)
            .HasRequired(e => e.Photo)
            .WithRequiredPrincipal(e => e.Product);

        modelBuilder.Entity<ProductPhoto>()
            .ToTable("Products")
            .HasKey(e => e.ProductId);

        base.OnModelCreating(modelBuilder);
     }
   }
}

推荐答案

执行此操作的最佳方法是使用 stub实体：仅具有ID值的实体对象：

The best way to do this is by using a stub entity: an entity object that's only got an Id value:

var product = context.Products.First();
var photo = new ProductPhoto { ProductId = product.ProductId }; // Stub
context.Entry(photo).State = System.Data.Entity.EntityState.Deleted;
context.Products.Remove(product);
context.SaveChanges();

如果您知道产品的I​​D您甚至可以仅创建两个存根就可以删除 Product 及其 ProductPhoto 。

If you know a Product's Id you can even delete both the Product and its ProductPhoto by only creating two stubs.

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