更新记录属性后，EF 在 SaveChanges() 上抛出 NullReferenceException .. 有时 [重复]

Question

我的简化数据库：

   +----------+
   |Products  |
   +----------+
   |ProductID |
   |ProdName  |
   |Desc      |
   |BrandID   |
   |CategoryID|
   +----------+

   +----------+
   |Brands    |
   +----------+
   |BrandID   |
   |BrandName |
   |ImageID   |
   |Desc      |
   +----------+

   +----------+
   |Categories|
   +----------+
   |CategoryID|
   |CategName |
   |ImageID   |
   |Desc      |
   +----------+

   +----------+
   |Images    |
   +----------+
   |ImageID   |
   |Path      |
   +----------+

   +----------+
   |ImageLinks|
   +----------+
   |ImageID   |
   |ProductID |
   +----------+

（注意：一个产品可以有多个图片，但一个品牌/类别最多可以有一个）

在 ASP.NET 中，

   using (DBEntities db = new DBEntities()) 
   {
         Product product = db.Products.FirstOrDefault(p => p.ProductID == 1);
         if (product != null) product.Desc = "any value";
         db.SaveChanges(); //works


         Image image = db.Images.FirstOrDefault(i => i.ImageID == 1);
         if (image != null) image.Path = "any value";
         db.SaveChanges(); //works

         Brand brand = db.Brands.FirstOrDefault(b => b.BrandID == 1);
         if (brand != null) brand.Desc = "the same value as the old description";
         db.SaveChanges();  //works

         Brand brand = db.Brands.FirstOrDefault(b => b.BrandID == 1);
         if (brand != null) brand.Desc = "some new description";
         db.SaveChanges();  //throws null reference exception

         Category categ = db.Categories.FirstOrDefault(c => c.CategoryID == 1);
         if (categ != null) categ.Desc = "the same value as the old description";
         db.SaveChanges();  //works

         Category categ = db.Categories.FirstOrDefault(c => c.CategoryID == 1);
         if (categ != null) categ.Desc = "some new description";
         db.SaveChanges();  //throws null reference exception
   }

这很奇怪！

这是 SaveChanges() 抛出的 NullReferenceException 的堆栈跟踪

Object reference not set to an instance of an object.
   at System.Web.UI.ParseChildrenAttribute.GetHashCode()
   at System.Collections.Generic.ObjectEqualityComparer`1.GetHashCode(T obj)
   at System.Collections.Generic.HashSet`1.InternalGetHashCode(T item)
   at System.Collections.Generic.HashSet`1.AddIfNotPresent(T value)
   at System.Collections.Generic.HashSet`1.UnionWith(IEnumerable`1 other)
   at System.Collections.Generic.HashSet`1..ctor(IEnumerable`1 collection, IEqualityComparer`1 comparer)
   at System.Collections.Generic.HashSet`1..ctor(IEnumerable`1 collection)
   at System.Data.Entity.ModelConfiguration.Utilities.AttributeProvider.GetAttributes(Type type)
   at System.Data.Entity.ModelConfiguration.Utilities.AttributeProvider.GetAttributes(PropertyInfo propertyInfo)
   at System.Data.Entity.Internal.Validation.EntityValidatorBuilder.BuildPropertyValidator(PropertyInfo clrProperty)
   at System.Data.Entity.Internal.Validation.EntityValidatorBuilder.BuildValidatorsForProperties(IEnumerable`1 clrProperties, IEnumerable`1 edmProperties, IEnumerable`1 navigationProperties)
   at System.Data.Entity.Internal.Validation.EntityValidatorBuilder.BuildTypeValidator[T](Type clrType, IEnumerable`1 edmProperties, IEnumerable`1 navigationProperties, Func`3 validatorFactoryFunc)
   at System.Data.Entity.Internal.Validation.EntityValidatorBuilder.BuildEntityValidator(InternalEntityEntry entityEntry)
   at System.Data.Entity.Internal.Validation.ValidationProvider.GetEntityValidator(InternalEntityEntry entityEntry)
   at System.Data.Entity.Internal.InternalEntityEntry.GetValidationResult(IDictionary`2 items)
   at System.Data.Entity.DbContext.ValidateEntity(DbEntityEntry entityEntry, IDictionary`2 items)
   at System.Data.Entity.DbContext.GetValidationErrors()
   at System.Data.Entity.Internal.InternalContext.SaveChanges()
   at System.Data.Entity.Internal.LazyInternalContext.SaveChanges()
   at System.Data.Entity.DbContext.SaveChanges()
   at VatechWebsite.Admin.Image_Upload.UploadBtn_Click(Object sender, EventArgs e) in c:\Users\Toshiba User\Desktop\vatech\VatechWebsite\VatechWebsite\Admin\Image_Upload.aspx.cs:line 109

PS：这是实体框架5

Answer 1

正如潜水员指出的那样，问题在于我有一个与 EF 生成的实体同名的类（类别和品牌）。参考这个帖子NullReferenceException in DbContext.saveChanges()

Answer 2

我认为您分配实体模型的对象类的方式不正确。 将以下更改应用于代码中的所有实体对象，然后尝试：

产品 product = db.Products.FirstOrDefault(p => p.ProductID == 1); /* 产品 */

对于类别、图片和品牌也是如此。

一切顺利。