参见英文答案 >
NullReferenceException in DbContext.saveChanges() 2个
我的简化数据库:
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:产品可以有多个图像,但品牌/类别最多只能有一个)
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 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