Article here

但它导致了

run time exception

如下.为什么？

我的连接字符串在App.config中正确配置.

我的应用程序是基于N层的.因此DbContext驱动类在数据层中.

这是我的连接字符串：

<add name="PawLoyalty" connectionString="Server=.;database=PawLoyalty;Trusted_connection=true;pooling=true;MultipleActiveResultSets=True" providerName="System.Data.sqlClient" />

我正在使用EF 4.1和vs 2010.

Running transformation: System.Reflection.TargetInvocationException: Exception has been thrown
by the target of an invocation.
—> System.ArgumentException: The argument ‘nameOrConnectionString’ cannot be null,empty or contain only white space.

at System.Data.Entity.ModelConfiguration.Utilities.RuntimeFailureMethods.ReportFailure(ContractFailureKind contractFailureKind,String userMessage,String conditionText,
Exception innerException)
at System.Data.Entity.DbContext..ctor(String nameOrConnectionString)
at PawLoyalty.Data.DataCatalog..ctor(Boolean allowLazyLoading) in D:\My Blog\Test
Projects\PawLoyalty\PawLoyalty\PawLoyalty.Data\DataCatalog.cs:line 31
at PawLoyalty.Data.DataCatalog..ctor() in D:\My Blog\Test Projects\PawLoyalty\PawLoyalty\PawLoyalty.Data\DataCatalog.cs:line 26
— End of inner exception stack trace —
at System.RuntimeTypeHandle.CreateInstance(RuntimeType type,Boolean publicOnly,Boolean noCheck,Boolean& canBeCached,
RuntimeMethodHandleInternal& ctor,Boolean& bNeedSecurityCheck)
at System.RuntimeType.CreateInstanceSlow(Boolean publicOnly,Boolean skipCheckThis,Boolean fillCache,StackCrawlMark& stackMark)
at System.RuntimeType.CreateInstanceDefaultCtor(Boolean publicOnly,StackCrawlMark&
stackMark)
at System.Activator.CreateInstance(Type type,Boolean nonPublic)
at System.Activator.CreateInstance(Type type)
at Microsoft.VisualStudio.TextTemplatingD6E95B37BD0790EBBCC7DB570AD3E2AC.GeneratedTextTransformation.GetEdmx(Type
contextType)
at Microsoft.VisualStudio.TextTemplatingD6E95B37BD0790EBBCC7DB570AD3E2AC.GeneratedTextTransformation.GenerateViews(String contextTypeName)
at Microsoft.VisualStudio.TextTemplatingD6E95B37BD0790EBBCC7DB570AD3E2AC.GeneratedTextTransformation.TransformText()
at Microsoft.VisualStudio.TextTemplating.TransformationRunner.RunTransformation(TemplateProcessingSession
session,String source,ITextTemplatingEngineHost host,String&
result)

更新

我的DbContext Derived类如下所示.

[Export(typeof(ISecurityDataCatalog))]
    [Export(typeof(IMappingDataCatalog))]
    [Export(typeof(IPawLoyaltyDataCatalog))]
    [PartCreationPolicy(CreationPolicy.NonShared)]
    public class DataCatalog : DbContext,IPawLoyaltyDataCatalog,ISecurityDataCatalog,IMappingDataCatalog
    {

        public static string ConnectionString { get; set; }
        public static string AccountToken { get; set; }

        public DataCatalog()
            : this(false)
        {
        }

        public DataCatalog(bool allowLazyLoading = false)
            : base(ConnectionString)
        {
            Configuration.LazyLoadingEnabled = allowLazyLoading;
        }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.ComplexType<DiscountValue>().Property(d => d.Fixed).HasPrecision(18,2);
            modelBuilder.ComplexType<DiscountValue>().Property(d => d.Percentage).HasPrecision(18,4);
            modelBuilder.Entity<InvoiceFee>().Property(d => d.Fixed).HasPrecision(18,2);
            modelBuilder.Entity<InvoiceFee>().Property(d => d.Percentage).HasPrecision(18,4);
            modelBuilder.Entity<InvoiceFee>().Property(d => d.Total).HasPrecision(18,4);
            modelBuilder.Entity<Invoice>().Property(d => d.Discount).HasPrecision(18,2);
            modelBuilder.Entity<Invoice>().Hasrequired(i => i.Appointment).WithOptional(a => a.Invoice).WillCascadeOnDelete(false);
            modelBuilder.Entity<InvoiceItem>().Property(d => d.Price).HasPrecision(18,2);
            modelBuilder.Entity<InvoiceItem>().Property(d => d.LatestTotal).HasPrecision(18,2);
            modelBuilder.Entity<InvoiceItem>().Hasrequired(i => i.Allocation).WithOptional(a => a.InvoiceItem).WillCascadeOnDelete(false);
            modelBuilder.Entity<InvoicePayment>().Property(d => d.Amount).HasPrecision(18,4);
            modelBuilder.Entity<ServicePrice>().Property(d => d.Price).HasPrecision(18,2);
            modelBuilder.Entity<ServiceBreedPrice>().Property(d => d.Price).HasPrecision(18,2);
            modelBuilder.Entity<ProviderPolicy>().Property(d => d.SalesTax).HasPrecision(18,4);
            modelBuilder.Entity<ProviderCredit>().Property(d => d.Balance).HasPrecision(18,2);
            modelBuilder.Entity<CombinedServiceDiscountDefinition>().Hasrequired(c => c.PrimaryService).WithMany().WillCascadeOnDelete(false);
            modelBuilder.Entity<CombinedServiceDiscountDefinition>().Hasrequired(c => c.SecondaryService).WithMany().WillCascadeOnDelete(false);

            modelBuilder.Entity<MedicalRecord>().Hasrequired(m => m.Pet).WithOptional(p => p.Medical).WillCascadeOnDelete(false);
            modelBuilder.Entity<BehavioralRecord>().Hasrequired(b => b.Pet).WithOptional(p => p.Behavioral).WillCascadeOnDelete(false);
            modelBuilder.Entity<DietRecord>().Hasrequired(d => d.Pet).WithOptional(p => p.Diet).WillCascadeOnDelete(false);

            modelBuilder.Entity<Provider>().HasOptional(p => p.Profile).Withrequired(p => p.Provider).WillCascadeOnDelete(true);

            modelBuilder.Entity<ProviderProfile>().HasOptional(p => p.Policy).Withrequired(p => p.Profile).WillCascadeOnDelete(true);
            modelBuilder.Entity<ProviderProfile>().HasOptional(p => p.CustomerRequirements).Withrequired(p => p.Profile).WillCascadeOnDelete(true);
            modelBuilder.Entity<ProviderProfile>().HasOptional(p => p.PaymentProfile).Withrequired(p => p.Profile).WillCascadeOnDelete(true);

            modelBuilder.Entity<Resource>().HasMany(r => r.Availability).Withrequired(a => a.Resource).WillCascadeOnDelete(true);

            Database.SetInitializer<DataCatalog>(null);
            base.OnModelCreating(modelBuilder);
        }

        public const string ServiceKey = "PawLoyalty";

        public DbSet<StreetAddress> StreetAddresses { get; set; }
        public DbSet<Appointment> Appointments { get; set; }
        public DbSet<Invoice> Invoices { get; set; }
        public DbSet<InsuranceCarrier> InsuranceCarriers { get; set; }
        public DbSet<PromotionCode> PromotionCodes { get; set; }

        // Provider Classes
        public DbSet<Provider> Providers { get; set; }
        public DbSet<ProviderProfile> ProviderProfiles { get; set; }
        //public DbSet<ProviderResourceItem> ProviderResourceItems { get; set; }
        public DbSet<Allocation> ResourceAllocations { get; set; }
        public DbSet<ResourceAvailability> ResourceAvailabilities { get; set; }
        public DbSet<Resource> Resources { get; set; }

        /// <summary>
        /// Wraps the object context detach method
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="t"></param>
        public void Detach<T>(T t) where T : class
        {
            // TODO: Is this needed? Hidden behind an interface in CTP5 implying infrequent usage.
            ((IObjectContextAdapter)this).ObjectContext.Detach(t);
        }

        // Owner Classes
        public DbSet<MedicalRecordOrder> Orders { get; set; }
        public DbSet<Owner> Owners { get; set; }
        public DbSet<Pet> Pets { get; set; }
        public DbSet<Breed> Breeds { get; set; }
        public DbSet<PetProvider> PetProviders { get; set; }

        // Security Catalog Items
        public DbSet<User> Users { get; set; }

        // Bing Maps Catalog items
        public DbSet<KnownLocation> KnownLocations { get; set; }
        public DbSet<KnownPostalCode> KnownPostalCodes { get; set; }

        public DbSet<QueuedEmail> QueuedEmails { get; set; }
        public DbSet<InvoicePayment> InvoicePayments { get; set; }
        public DbSet<Employee> Employees { get; set; }
        public DbSet<Schedule> Schedules { get; set; }
        public DbSet<Subscription> Subscriptions { get; set; }
        public DbSet<EmailSubscription> EmailSubscriptions { get; set; }

        public DbSet<ResourceAvailabilityUpdate> ResourceAvailabilityUpdates { get; set; }
        public DbSet<EmployeeAvailabilityUpdate> EmployeeAvailabilityUpdates { get; set; }
        public DbSet<InvoiceConfiguration> InvoiceConfigurations { get; set; }

        public DbSet<Vaccine> Vaccines { get; set; }
        public DbSet<TourEmail> TourEmails { get; set; }
        public DbSet<ReservationRequest> ReservationRequest { get; set; }
        //public DbSet<ReservationRequestPets> ReservationRequestPets { get; set; }
        public DbSet<Vaccination> Vaccinations { get; set; }
        public DbSet<SpecialInstruction> SpecialInstructions { get; set; }

        public DbSet<Product> Products { get; set; }
        public DbSet<ProductCategory> ProductCategories { get; set; }
        public DbSet<VendorStock> VendorStocks { get; set; }
        public DbSet<ShoppingCart> ShoppingCarts { get; set; }
        public DbSet<SaleDetail> SaleDetails { get; set; }
        public DbSet<Sale> Sales { get; set; }
        public DbSet<SalePayment> SalePayments { get; set; }

        public DbSet<PetService> PetServices { get; set; }
        public DbSet<PetServicePrice> PetServicePrices { get; set; }

        public DbSet<MiscProperty> MiscProperties { get; set; }
        public DbSet<ProviderMiscProperty> ProviderMiscProperties { get; set; }

        public DbSet<ProviderAuthorizedCreditCard> ProviderAuthorizedCreditCards { get; set; }
        public DbSet<AuthorizedCreditCard> AuthorizedCreditCards { get; set; }
        public DbSet<ProviderPackage> ProviderPackages { get; set; }

        public DbSet<ProviderEmailPreference> ProviderEmailPreferences { get; set; }
        public DbSet<EmailType> EmailTypes { get; set; }

        public DbSet<RetailSaleReturn> RetailSaleReturns { get; set; }
        public DbSet<ServiceRefund> ServiceRefunds { get; set; }

    }